DPanswers
Buying Flash for the Canon System
Table of Contents
1. Introduction
This note is intended to serve as background information to first time buyers of a flash to a Canon digital camera with built-in support for E-TTL (Evaluative Trough The Lens) or E-TTL II flash exposure control.
(If you are looking for my notes on Nikon flash, see here.)
Most of this note discusses Canon's dedicated units (i.e. flashes sold by Canon that are compatible with E-TTL), or third party dedicated units (i.e. flashes sold by others that are compatible with E-TTL), but there is also a brief discussion about using generic (non-dedicated) flashes on Canon DSLRs. Even if your camera can make use the E-TTL, you may want to use a generic flash. Studio lighting is often built around generic strobes, generic flashes are often cheaper than dedicated, and of course, generic flashes may also be used on non-Canon systems. The downside of generic flashes is that they lack some of the advanced features of dedicated flashes.
Canon's E-TTL
In 1995, with the EOS Elan II camera, Canon introduced a new, sophisticated flash control system, known by the abbreviation E-TTL (Evaluative Trough The Lens). It replaced and obsoleted the earlier TTL and A-TTL systems.
Users familiar with Canon's TTL on their film cameras will notice a subtle difference when moving on to E-TTL. In the case of the E-TTL, the power of the flash is not controlled during the exposure by measurement off the film surface itself. Off-the-film (OTF) measurement is not possible with digital cameras as the sensor's surface is not appropriate for measuring off. This factor, combined with the decreased latitude of the digital sensor when compared to film means that the E-TTL user must expect slightly less accuracy when using E-TTL, compared to the traditional OTF TTL measurement used on a film camera.
Instead E-TTL relies on something called pre-flash for exposure control. It works like this: The camera fires a low power pre-flash milliseconds before the shutter opens. It then measures the light from this pre-flash as it is reflected from the subject through the lens (TTL). The camera uses this reading to compute the power ratio for the flash for correct exposure. The camera communicates the desired power-ratio to the flash and the flash adjust its power accordingly. Finally, the camera opens the shutter and fires the flash to make the exposure. The E-TTL system provides a fully automatic exposure control that seamlessly integrates camera and flash, but the pre-flash sequence also introduces a tiny shutter delay.
E-TTL is a dedicated flash system that is supported by the some of Canon's film bodies, and all their DSLR models. I am less sure of how well supported E-TTL is by Canon's compact digicams, but at least the more advanced compact cameras such as the Pro 1 and the Powershot G-series supports at least some E-TTL features. Point and shoot Canon compacts such as the Ixus-series do not support external E-TTL flashes and are outside the scope of this article. To make sure what features are supported, check the manual for the particular model you are interested in.
Newer Canon cameras use an inproved version of the E-TTL system, called E-TTL II. For instance, E-TTL II is programmed to ignore highlights reflected by shiny surfaces, which tended to fool E-TTL into underexposing. The most significant difference from E-TTL is that E-TTL II is capable of taking the focus distance as reported by the lens into account when computing flash output (similar to Nikon's i-TTL system). However, not all Canon lenses report focus distance to the body.
Because the difference between E-TTL and E-TTL-II is in the body, not the flash, any E-TTL capable flash will give you E-TTL II metering when put on a E-TTL II capable EOS body (i.e. all Canon DSLRs except 1D, 1Ds, D30, D60, 10D and 300D) with an E-TTL-II compatible lens. In the remainder of this note, for brevity I just write E-TTL instead of E-TTL and E-TTL II.
The major features of E-TTL are:
- Aperture, ISO, focal length and flash colour information communicated between flash and body.
- E-TTL (Evaluative Trough The Lens) flash exposure control.
- Makes use of focus distance with lenses capable of communicating this to the body (E-TTL II).
- Wireless (by light) control of off-camera flash units.
- FEL (Flash Exposure Lock) to obtain correct flash exposures for off-centre subjects.
- FEC (Flash Exposure Compensation ) to get correct flash exposures for non-average subjects.
- FEB (Flash Exposure Bracketing) to take three pictures, each with a different amount of FEC.
- FP (Focal Plane) high-speed sync to synchronize flash at high shutter speeds.
- AF-assist illuminator (to ensure fast and precise autofocus in the dark).
Not all features are available on all compatible models. See the manuals and specifucation sheet for the model you are interested in for details.
E-TTL works through a very high level of integration between the camera body and one or more Canon Speedlites. To use E-TTL, the body and the flash guns need to be compatible with E-TTL.
2. Flash Units
This section discusses the different type of flash units that one can buy for the Canon system, starting with Canon's own dedicated units, then some third party dedicated units, and finaly generic flash units that one may use on a Canon system.
In the summaries below, all guide numbers (GN) are given in meters, for ISO 100. For guide numbers in feet, multiply by 3.3. To convert to a different sensor speed, multiply the ISO 100 GN with the square root of the ISO ratio. Note that for flashes with a zoom head, the guide number (GN) is listed for with the zoom set to 35mm, 50mm and maximum zoom (assuming a FX-sized sensor). The number you'll find in most manufacturer's literature is usually for maximum zoom only, which makes these flashes seem more powerful than they really are. The “m/s” colum indicates if can be used as a master and/or slave in Canon's wireless flash control system. For generic flashes, the column “Slave” indicates if the flash has a built in optical slave function.
The summaries only lists some of the features of each flash. If you want to know all the technical details and features, please see the manufacturers' specification sheets.
Dedicated Canon Units
To be able to use E-TTL on a Canon camera, you need an E-TTL capable flash. Neither the original TTL nor A-TTL system work with these digital cameras, but the older TTL/A-TTL Speedlites (and dedicated third party flash guns supporting TTL/A-TTL) may be used in manual mode (see below).
At the time og writing, the following Canon Speedlites support at least E-TTL exposure control:
| Model | Coverage | GN (ISO 100/meter) | m/s | Cost | Notes | ||
|---|---|---|---|---|---|---|---|
| f=35mm | f=50mm | f=max | |||||
| ST-E2 | - | - | - | - | m/- | USD 210 | (1) |
| MR-14EX | - | - | - | 14 | m/- | USD 450 | (2) |
| MT-24EX | - | - | - | 22 | m/- | USD 650 | (3) |
| 220EX | 28mm | - | - | 22 | -/- | USD 120 | (4) |
| 270EX | 28, 50mm | 22 | 27 | 27 | -/- | USD 150 | (5) |
| 380EX | 24-105mm | 28 | 31 | 38 | -/- | USD 160 | (6) |
| 420EX | 24-105mm | 31 | 34 | 42 | -/s | USD 200 | (7) |
| 430EX | 14, 24-105mm | 31 | 34 | 43 | -/s | USD 250 | (8) |
| 430EX2 | 14, 24-105mm | 31 | 34 | 43 | -/s | USD 330 | (9) |
| 550EX | 17, 24-105mm | 36 | 42 | 55 | m/s | USD 350 | (10) |
| 580EX | 14, 24-105mm | 36 | 42 | 58 | m/s | USD 380 | (11) |
| 580EX2 | 14, 24-105mm | 36 | 42 | 58 | m/s | USD 410 | (12) |
Additional exposure modes and other distinguishing features are listed in the notes below, but for a full list of features, see the full specificatons at Canon's website or this alternate page.
- Dedicated transmitter for E-TTL wireless flash system.
- Macro ring flash.
- Macro twin flash.
- No tilt or swivel. Discontinued 2009.
- Manual 1-1/64. No swivel.
- No swivel. Discontinued 2001.
- Discontinued 2005.
- Manual 1-1/64. Discontinued 2008.
- Manual 1-1/64.
- Manual 1-1/128. Discontinued 2005.
- Manual 1-1/128. Discontinued 2007.
- Manual 1-1/128. Non-TTL auto.
Canon's older zoom head flashes do not take crop factors into account when zooming. This is not a problem with Canon compact cameras because their interface seamlessly convert actual focal lengths to 135 film FOV – but it wastes power when used on a digital camera with a sensor smaller then the 135-format negative such as the Canon EOS 1000D, 450D, 40D and 1DMkIII by zooming out too wide. Canon's newer Speedlites, such as the 430EX, 430EX2, 580EX and 580EX2, compensate for this.
Note: The initial batches of the Canon 580EX (mk I) were faulty. These Speedlites would compensate for sensor size for normal and tele lenses, but would give severe vignetting if used with wide angle lenses (below f=24mm) on a body with a small (1.6x crop) sensor. Canon silently corrected this problem some time in 2005, but has still to acknowledge the problem publicly. According to this thread at DPReview, Canon UK has started replacing or repairing faulty units under guarantee, while service centers in other locations may still not acknowledge the problem. If you are planning to buy a used 580EX to use with a camera with a non-FX sensor (e.g. EOS 1000D, 450D, 40D), you should be careful if the serial numbers on the 580EX starts with 0 or 1, and test the unit for this problem prior to purchase to avoid being stuck with a broken unit.
In 2007, Canon replaced the 580EX with the 580EX mk II (580EX2), which has the following improvements compared to the mk I:
- Environmental seals (weatherprooing).
- More solid build, including a metal foot.
- PC socket.
- 20 % faster recycling times.
- Silent recycling.
- WB info communicated to a compatible camera.
- Flash settings can be controlled from a compatible camera menu (i.e. models produced after 2007).
- Sensor for auto mode in addition to E-TTL.
Dedicated Third Party Units
A number of third part flashes exists that are claimed by their manufacturers to be compatible with Canon's flash system. This usually means that they at least are capable of making use of E-TTL for power control. Below is usage notes for the some of these third party dedicated flashes.
Disclaimer: I do not own our use any third party dedicated flash unit. The notes below about using them has been pulled from private communications with users, and from manuals, discussion forums, and other public sources. I've included it here “as is”. The information may not be complete or correct, and corrections are welcome.
Metz
I am currently aware of the following flashes from Metz's lineup that supports at least E-TTL exposure control.
| Model | Coverage | GN (ISO 100/meter) | m/s | Cost | ||
|---|---|---|---|---|---|---|
| f=35mm | f=50mm | f=max | ||||
| 28 AF-3C | 24, 35, 85mm | 22 | - | 28 | -/- | USD 140 |
| 44 MZ-2 | 28-105mm | 26 | 34 | 44 | -/- | USD 294 |
| 45 CL-4 D | 28, 35mm | 45 | - | 45 | -/- | USD 650 |
| 48 AF-1C | 18, 24-105mm | 29 | 36 | 48 | -/s | USD 200 |
| 54 AF-1C | 20, 24-105mm | 31 | 40 | 54 | -/- | USD 340 |
| 54 MZ-4 | 20, 24-105mm | 31 | 40 | 54 | -/- | USD 340 |
| 58 AF-1C | 18, 28-105mm | 32 | 42 | 58 | m/s | USD 350 |
| 76 MZ-5 | 20, 24-105mm | 46 | 54 | 76 | -/- | USD 890 |
For more detailed specifications, see Metz's own web. For detailed information about compatibility, see the compatibility chart found on that page, as compatibility varies with firmware versions for some of the models. Some the the Metz flash guns have a USB-interface to let users upgrade the firmware for newer camera models.
The flash guns with the AF designation are dedicated shoe mount flashes that are built to work with a single, dedicated flash system (in this case Canon's E-TTL). The flash guns with the MZ and CL designations are based upon Metz SCA-system. In the SCA-system the flash is generic, but is tied into a particular dedicated system with a suitable adapter (typical cost USD 80 per adapter). You may move a flash to a different system by buying the right adapter for that system.
Metz flash guns in general has an excellent reputation for performance and build quality, but the only user report I've seen on the 58 AF1-1C was negative. Sensitivity when used as a remote unit was lower, and the zoom head would sometines jam.
Quantum
Quantum sells a very powerful (and expensive) modular flash system with lots of options and interchangable parts that are claimed to be E-TTL compatible.
| Model | Reflector | GN (ISO 100/meter) | m/s | Cost | ||
|---|---|---|---|---|---|---|
| f=35mm | f=50mm | f=max | ||||
| Qflash 4d | interchangable | 35 | 50 | 70 | -/- | USD 610 |
| Qflash 5d-R | interchangable | 50 | 70 | 95 | m/s | USD 700 |
For more detailed specifications, see the Quantum website.
Like the Metz SCA-system the Qflash-system is generic, but is tied into a particular dedicated system with a suitable adapter (typical cost USD 166 per adapter). You may move a flash to a different system by buying the right adapter for that system.
Note that the QFlash-system is very modular and that guide number depends on both what refector you fit, and what power pack you use.
I haven't tried these strobes, but they have an excellent reputation. They are generally rated higher for accurate exposure that Canon's own Speedlites.
Sigma
Sigma's lineup contains five flashes that supports at least E-TTL exposure control. These are:
| Model | Coverage | GN (ISO 100/meter) | m/s | Cost | ||
|---|---|---|---|---|---|---|
| f=35mm | f=50mm | f=max | ||||
| EM-140 DG Macro EO-ETTL | - | - | - | 14 | m/- | USD 359 |
| EF-500 DG ST EO-ETTL | 17, 28-105mm | 29 | 36 | 50 | -/- | USD 150 |
| EF-500 DG Super EO-ETTL | 17, 28-105mm | 29 | 36 | 50 | m/s | USD 219 |
| EF-500 DG ST EO-ETTL II | 17, 28-105mm | 29 | 36 | 50 | -/- | USD 150 |
| EF-500 DG Super EO-ETTL II | 17, 28-105mm | 29 | 36 | 50 | m/s | USD 219 |
| EF-530 DG ST EO-ETTL | 17, 24-105mm | 31 | 40 | 53 | -/- | USD 169 |
| EF-530 DG Super EO-ETTL | 17, 24-105mm | 31 | 40 | 53 | m/s | USD 239 |
| EF-530 DG ST EO-ETTL II | 17, 24-105mm | 31 | 40 | 53 | -/- | USD 169 |
| EF-530 DG Super EO-ETTL II | 17, 24-105mm | 31 | 40 | 53 | m/s | USD 239 |
For more detailed specifications, see Sigma's own web.
The EF-530 series is a direct replacement for the EF-500 series. It has slightly more power and the zoom head zooms out to 24mm, but as far as I know, nothing else has changed. There are also some variations within the EF-530 series, see notes on compatibility below.
The Sigma flashes gives slightly more bang for the buck than Canon's own flashes. However, the build is less solid, some users report erratic exposure control, and the user interface is less intuitive. On the other hand, the Sigma 500/530 DG Super can also be used as a plain optical slave (without E-TTL), and none of Canon's Speedlites have that capability.
The Sigma 500/530 DG (ST and Super) flashes have a fair reputation for E-TTL compatibility. They lack some features compared to Canon 580EX2, such as adapting the zoom head to the crop factor, custom functions, and a high voltage socket. The “Super” models can be used as master or slave in Canon's wireless flash control system, as well as a plain optical slave. It also has more sophisticated manual controls (8 steps vs. 2 steps). Other features of the “Super” lacking from the “ST” are on-flash FEC, FP mode, strobe mode, an LCD panel, and the ability to be trigged by a simple two-contact hot-shoe.
If you are buying a second-hand Sigma flash (or “old” new stock), note that there are some compatibility issues:
- There exists a version designated “500 Super” and “500 ST” (i.e. no “DG” as part of its model designation). This version is not fully compatible with digital Canon cameras.
- With the Canon EOS 50D DSLR (and only this model so far), there are also some compatibility issues (the zoom head does not work properly, and exposure is not correct.) with models that have “DG” as part of the model designaton. See this notice to customers using Sigma's EO-ETTL II type flashguns for details.
See also note below about firing a Sigma's flash from an optical or radio trigger.
Others
There also exists a number of other flash guns that are claimed by their manufacturers to support at least E-TTL exposure control.
| Model | Coverage | GN (ISO 100/meter) | Cost | ||
|---|---|---|---|---|---|
| f=35mm | f=50mm | f=max | |||
| Bower SFD14C Macro | - | - | - | 14 | USD 120 |
| Bilora D140 RF-C Macro | - | - | - | 14 | USD 120 |
| Digital Concepts 528AF/CAN | 35mm | - | - | 22 | USD 40 |
| Vivitar DF22-C | 28-85 | 19 | 22 | 27 | USD 40 |
| Sunpak PF30X | 30mm | - | - | 30 | USD 100 |
| Sunpak PZ40X II | 24-80mm | 28 | 30 | 40 | USD 150 |
| Sunpak PZ42X | 24-105mm | 28 | 30 | 42 | USD 156 |
| Phoenix 99C | 28-85mm | 28 | 30 | 40 | USD 75 |
| Promaster 7500DX | 24-105mm | 29 | 32 | 42 | USD 140 |
| Quantaray 900WA | 24-105mm | 29 | 32 | 42 | USD 180 |
| Bower SFD35C | 28-85mm | 29 | 34 | 42 | USD 90 |
| Phoenix DZBIS 112CII | 28-85mm | 29 | 34 | 42 | USD 90 |
| Vivitar DF340ZC | 28-85mm | 29 | 34 | 42 | USD 60 |
| Digital Concepts AFI | 24-85mm | 25 | 32 | 42 | USD 115 |
| Nissin Di622 | 16, 24-105mm | 26 | 34 | 44 | USD 170 |
I haven't tried any of these either, and know little about their quality and how compatible they really are.
I have received the following comment from Alan Williams:
“Nissin i622 for Canon: This week I have received three of these from Warehouse Express who are providing really good after sales service. Unfortunately, I cannot get any of the three units to function satisfactorily. One fails to fire when in Slave mode. Another will not fire in Tv or Av. None will provide a vibrant exposure in E-TTL, always underexposing.”
Øivind Stuan writes at Foto.no (my translation from Norwegian):
“ I've used Di622 in a couple of months now and am happy with the unit, given its pricetag.
Good:
- The E-TTL seems to work well.
- Optical slave works very well indoors with an E-TTL-flash as master.
- Build-in bounce card and diffuser plate for wide angle use (also handy for use with umbrella, given that the unit lacks manual zoom).
- Hodet kan vinkles 180/90 grader til høyre/venstre, samt 0/45/60/75/90 grader oppover (fungerer også fint i vinkler mellom de faste trinnene).
Less good:
- Det er dessverre ikke mulig å justere zoom manuelt, den styres automatisk av kameraet når blitzhodet rettes forover. I alle andre retninger settes blitzhodet til zoom tilsvarende 50mm brennvidde.
- Kan i praksis ikke brukes med billige radiotriggere da blitzen går i dvale etter 5 sekunder når den settes i manuell modus. Hvis den sitter montert på kameraet eller i enden av en TTL-kabel vekkes den automatisk når utløseren trykkes halvveis ned, men dette skjer ikke når man kun gir signal på senterpinnen.
- Den optiske slaven reagerer ikke på en manuell blitz, det må være TTL (den innebygde i kameraet fungerer fint). I sterkt lys utendørs fungerer den naturligvis dårligere.
- Diffuserplaten ser ut til å lage et svakt synlig mønster i lyset når blitsen brukes direkte.”
If you have anything to share about one of these units, or just would like to comment, please user the blog.
Generic Units
Generic flash units are are flash units that will work on your Canon DSLR, but are not designed to be compatible with E-TTL. Most of these units offer at least manual (usually with adjustable power ratio) and non-TTL auto exposure modes, but obviously not E-TTL.
There exists too many generic flash models, both new and used, for me to list them all here, but the following list gives examples of some popular generic units that offer both non-TTL auto and manual with variable power settings, including some discontinued Nikon Speedlites:
| Model | Coverage | GN (ISO 100/meter) | Slave | Cost | ||
|---|---|---|---|---|---|---|
| f=35mm | f=50mm | f=max | ||||
| Nikon SB-50DX | 14, 24-50mm | 22 | 26 | 26 | - | - |
| Sunpak 383 Super Auto | 35mm | 35 | - | 35 | - | USD 80 |
| Vivitar 285HV | 28-105mm | 31 | 37 | 43 | - | USD 90 |
| Metz 44 MZ-2 | 28-105mm | 29 | 34 | 44 | yes | USD 294 |
| Nikon SB-26 | 18, 24-85mm | 36 | 42 | 50 | yes | - |
| Nikon SB-28 | 18, 24-85mm | 36 | 42 | 50 | - | - |
| Nikon SB-28DX | 18, 24-85mm | 36 | 42 | 50 | - | - |
| Nikon SB-80DX | 14, 24-105mm | 38 | 44 | 56 | yes | - |
If you want to use a generic auto
or manual flash with your Canon camera, you first need to figure out
how to connect the flash to the camera. As noted in the section on
flash trigger voltage below, Canon's recommendation
is that you should only mount one of the Canon's own Speedlites in the
hot-shoe.
Canon's higher end DSLRs (e.g. EOS 10D, 20D, 30D, 40D, 5D, 1D-series) comes with a pc-socket, that can be used to trigger generic auto and manual flash units. The maximum safe voltage rating for the pc-socket can be found in your camera's manual. For all current models, I belive it is 250 volts.
To hook up a flash to the pc-socket, you just plug the pc-plug from the flash into the camera's pc-socket. If you want to use the camera's hot-shoe to hold the flash, I recommend that you convert it into a cold-shoe by putting insulating tape over the contacts to avoid any electrical connection between camera and flash through the shoe.
If your flash does not come with a pc-plug, you can buy a cheap pc-to-hot-shoe adapter, such as the model displayed above, to make the connection. You connect the adapter to the camera's pc-socket, and mount the flash in the adapter's hot-shoe.
Most generic flashes will also work if you mount them in the hot-shoe. However, because of the hazards associated with high trigger voltages you should be aware of the risks involved.
Dedicated flashes built for a different system (e.g. the older Canon E, EG, EZ, ML and TL Speedlites and Nikon Speedlights) will in most cases not fire from the hot-shoe, but may work fine with the pc-to-hotshoe-adapter. (However, there are user reports that Canon is quietly improving support for use of older flashes. In particular, firmware ver. 1.0.5 for the EOS 400D/Digital Rebel XTi/, released in April 2007, is reported to make a number of older flashes work in the hotshoe again.).
Canon's compacts and entry level
DSLRs do not have a pc-connector. For these cameras, a possible
workaround is to use a cheap hot-shoe-to-pc-adapter such as the
adapter shown on the left, in the camera's hot-shoe. You can then
connect the flash's pc-plug to the adaper's pc-socket. Since the
adapter is plugged directly into the camera's hot-shoe, you should
only do this if you know that the flash's
trigger-voltage is safe.
However, my preferred set-up for using non E-TTL flashes on my Canon Powershot G5 (which have no pc-connector) is to use a very cheap chinese radio slave. For details, see: this page. This also removes any trigger-voltage worries, because the third-party flash is never in physical contact with the camera.
For use of plain optical slaves with a Canon digital camera, see notes on slave use below.
3. Exposure Modes
In order to have the scene properly lit, with correct exposure and with a good balance between foreground and background light, we need to control the amount of light put out by the light, and adjust aperture, shutter speed and ISO to match that, as well as the ambient light. In this note, the following flash exposure control modes will be discussed:
- TTL automatic flash mode (E-TTL II, E-TTL, A-TTL and TTL – available on Canon EX Speedlites and some dedicated third party flashes). When you are using TTL automatic flash mode, the correct power to use for flash is determined by measuring the amount of flash light reflected by the entire scene or foreground subject through the camera lens (TTL = Through The Lens).
- Non-TTL Auto flash mode (available on Canon 580EX2 and some generic flashes). When you use a non-TTL Auto flash mode, you use a built-in sensor at the front of the flash that measures the average flash light reflected by the entire scene.
- Manual mode (available on some Canon Speedlites and generic flashes). When you use a Manual flash mode, nothing measures the light, you control exposure by setting up the power of the flash by selecting how much (as a fraction of maximum output) light the flash should emit, and selecting a ISO and aperture that will yield the right exposure.
TTL
E-TTL is the name for Canon's dedicated metering system for high-end digital cameras. It replaces and obsoletes the earlier TTL and A-TTL systems. This note only discusses E-TTL, not the obsolete version of Canon's TTL.
Canon's E-TTL flash exposure system is a complex interplay between the camera and the flash. Because the system is highly automated, with its own built-in logic, it is sometimes behaves like it has a mind on its own. Without understanding this internal logic, it is difficult to predict how the flash will behave in different situations.
To make matters even more complex, the way Canon has set up E-TTL varies to some extent from camera to camera. These variations originate partly from physical constraints (such as the placement of focusing points and flash sensors) and partly from subtle design variations.
Below is my understanding of how Canon's E-TTL flash exposure system works. Canon's documentation does not go into much detail about E-TTL, so the findings below is based upon my limited experiences with the system on equipment I have used, and may therefore be inaccurate. Corrections and additions are welcome.
Some EOS bodies let you choose between two flash metering modes by use of custom functions. These modes are called “average” and “evaluative”. If the camera don't offer alternative modes, you should assume that it uses evaluative flash metering.
E-TTL is based upon measuring the flash light reflected from the scene through the camera's lens. The measurement is done by firing a low-power pre-flash. The delay between the pre-flash and actual flash is so short that the human eye is not able to distinguish between them. (However, the pre-flash will trigger plain optical slave strobes, so in order to use these type of slaves, you need to disable the pre-flash.)
When the pre-flash fire, the light reflected by scene is picked up by one or more internal sensors. If the body has multiple focus points, there will be a separate metering at each focus point. Canon calls this AIM (Advanced Integrated Multipoint) metering.
These measurements are used to compute how much power to use for the actual flash. If you use auto focus and evaluative mode, the reading is biased towards the sensor area corresponding to the active focus point. In average mode, the measurement is averaged for the entire frame. If you use average mode, the flash works as main flash and the internal logic seems to be much less sophisticated than evaluative mode. The discussion below focuses on how the flash works in evaluative mode.
Note that the AIM system means that in evaluative mode, it is best to rely on selecting off-centre focus points for flash photography rather than using the centre point and then recomposing the image. (unless you use FEL, flash exposure lock).
In evaluative mode Canon's E-TTL flash exposure system is set up to work as either main flash or fill flash. As main flash, it will try to expose for the main foreground subject, and let the shadows fall wherever they fall. As a fill flash, it will adjust the camera's aperture and shutter speed to correctly expose the background, and adjust the flash power to fill in the foreground so that it matches the surroundings.
The first rule of E-TTL is to understand that the default settings that Canon has selected for flash photography are rather extreme, with a strong bias towards settings that work fairly well when the flash only being used to “fill in” the ambient lighting, but with a tendency to underexpose when the flash is used as the main light. The good news is that the settings can be adjusted, and Canon expect you to understand how and when to do so. Here is an excerpt from an answer from Canon on the subject of the tendency of the 580EX to underexpose when used as main flash:
“The 580EX Speedlite is equipped with functionality to either overexpose or underexpose, depending on how you manage it's controls. The EOS camera also has custom functions to manage flash exposures with '+' or '-' exposure compensation. If you take the time to properly understand how the custom functions of your Speedlite work in conjunction with the custom functions in your camera, you will be impressed with their capabilities.”
To cut a long story short, until you've gained enough experience with E-TTL to dial in the required flash exposure compensation (FEC) without even thinking about it, fire frequent test shots and use your camera's histogram as a flash exposure meter. Set FEC if necessary. About +1 stop FEC when using an E-TTL flash as main flash is a common setting.
The second rule of E-TTL is that (except in the special FP high speed sync mode) the system will never let you exceed the maximum x-sync speed (1/200 or 1/250 second on most Canon models). When optimizing for main flash, the minimum shutter speed will be limited to 1/60 second for best handheld performance. When optimizing for fill flash, it may stretch the exposure to as much as two seconds.
The drawback of using main flash is that photos taken in dimly lit areas usually end up with a black or very dark background. The drawback of using fill flash is that dark surroundings may lead to very slow shutter speeds (Av mode), making it necssary to use a tripod and for subjects to hold still to avoid blur, or a too wide aperture (Tv mode) with a depth of field that does not suit the scene..
Whether the system optimizes for main flash or fill may depend upon on the type of Canon camera, the setting of the camera's mode wheel, and the ambient light.
With the camera's mode wheel set to program mode (P), auto mode (Auto, and/or green rectangle) and most of the “scene” modes (i.e. the modes identified by small icons), something like the following algorithm is appearently used to decide whether to optimize for main flash or for fill flash: If the ambient light level is suitable for handheld shots (i.e. EV 11 or higher, typically open shade or heavy overcast daylight), the system optimizes for fill flash. If the scene is darker, the system optimizes for main flash. In both cases, the program will try to use the fastest shutter speed/widest aperture possible within the other constraints. The lowest shutter speed the camera will select in these modes is 1/60th of a second.
Some say that the third rule of E-TTL is that you should never use auto mode, program mode (P), or any of the “scene” modes. To many users, the camera's behaviour when using these modes in combination with E-TTL flash is just too counter-intuitive to be helpful. YMMV, but you should be aware that these modes may not be the simplest to master with E-TTL flash. Many users of Canon DSLRs (as opposed to a compacts), recommend putting the camera in manual mode when using E-TTL indoors, and aperture priority (Av) for fill flash outdoors in daylight.
When you use P, auto or one of the scene modes, you are essentially telling the camera to do pick the settings to use for you. If you want to pick the settings, you should use M, Av or Tv.
With the camera's mode wheel set to manual mode (M), aperture priority (Av), or shutter speed priority (Tv), behaviour depends on the type of camera.
Canon DSLRs is by default set up to use the Av and Tv modes for fill flash. You set the aperture (Av) or shutter speed (Tv), and the DSLR will adjust the shutter speed (up to two seconds) or aperture to expose the background for the ambient light. Flash power is adjusted to just fill in the foreground. However, most Canon DSLRs have a custom setting that let you change the shutter speed constraint in Av mode.
In Canon's compact models, such as the Powershot-series, the Av and Tv modes work similar to the P mode and the camera will never select a shutter speed slower than 1/60th second.
Some Canon camera's (i.e. compacts and consumer DSLRs such as the 350D) has a “scene” mode called Night Scene that will fire the flash to correctly expose the forground subject while extending the exposure for up to two seconds to also capture the surroundings.
In manual mode (M) you can set both the aperture and the shutter speed to whatever you want. In Canon DSLRs, the E-TTL-system in M mode will measure the light reflected by the foreground subject and adjust flash power to expose the foreground correctly. To get fill flash in M mode, set the aperture and shutter speed to correctly expose the background, and the E-TTL-system will take care of the foreground.
Many people find that the simplest way to use E-TTL flash with a Canon DSLR, is to put the flash on automatic E-TTL (ETTL) and the camera on manual (M). Then select a suitable combination of shutter speed and aperture (e.g. 1/100 second and f/8.0). With this setting, the flash will automatically be adjusted to expose the foreground adequately, while the background exposure is determined by the shutter/aperture combination. If your choice of shutter speed exceeds the x-sync speed of your camera (1/200 or 1/250 second on most Canon models), you also need to use the FP high speed sync mode on the flash.
In manual mode (M), Canon compacts such as the Powershot G5 switches off the pre-flash (and thereby E-TTL). This makes it feasible to use plain optical slaves, that otherwise are disturbed by the pre-flash. This has the unfortunate side effect that E-TTL can not be used to control the power of the flash in manual mode (see p. 101 in the Powershot G5 manual for details).
Because Canon's peculiar preference for fill-flash, you may find that the camera warns about severe underexposure when you use settings suitable for main flash. These may be confusing until you learn to ignore them.
The big advantage of E-TTL is that because E-TTL measures reflected light through the camera's lens, the position of the flash (or flashes) does not matter. The flash may be in or out of the hot-shoe, facing away from the camera or even put inside a softbox. The set-up may involve multiple flashes controlled by Canon's wireless flash control system. No matter what, E-TTL metering means that the camera meters the actual scene as seen through the lens. The sensor on an non-TTL Auto flash may “see” the wrong scene in many situations where the flash is off-camera.
Auto
Non-TTL Auto first appeared in the 1970ies and was the preferred method for controlling flash exposure until well after dedicated flash systems built around some form of TTL light measurement debuted around 1980.
Some argue that modern TTL technology, such as E-TTL, has made Auto obsolete. However, you can still buy cheap and powerful generic flashes using Auto for exposure control (e.g, Vivitar 285HV, Sunpak 383 Super Auto and Metz 44 MZ-2). Canon has retained the Auto mode in the EX-series, but at the time of writing only the Canon 580EX2 offers Auto mode in addition to E‑TTL.
In Auto mode, the flash uses a built-in sensor that measures the average light reflected from the scene and shuts off flash power when the sensor indicates that the subject is properly lit. The measurement is done in real-time, during the actual exposure. Unlike E‑TTL, there is no pre-flash when you use Auto to control exposure.
The exposure metering in Auto mode is simple and predictable when used for main flash. Most photographers learn how to compensate for the errors that the system introduces in difficult lighting situations.
Unless the flash is made to communicate with the camera (see below), to use an auto flash you need to set the camera up in manual mode (M). You then select a shutter speed equal to the camera's maximum x-sync speed or less, and a suitable aperture and ISO-value. You dial in the same aperture and ISO on the flash and you are ready to shoot.
Some flashes with Auto mode, such the Canon 580EX2 and the Metz 54 MZ, are built to communicate with the camera through the hot-shoe, and automatically gets the aperture and ISO-value from the camera. In that case, you may can leave the camera in P or Av mode, and work with camera and flash just as tightly integrated as if you were using E‑TTL.
As long as the flash is fixed to the hot-shoe, auto flashes, when tilted or rotated, has a metering sensor that still measures along the same axis as the lens. This means that the flash metering system will automatically compensate for any light loss that is the result of (for instance) bouncing the flash light against a ceiling. But if the flash is used out of the hot-shoe, the fact that the flash sensor is no longer aligned with the camera may cause problems. For instance, if you put an auto flash inside a softbox, the flash sensor will measure the light reflected inside the softbox and not the light reflected from the actual scene. To get around this limitation, some auto flashes has a detachable sensor that can be mounted in the camera's hot-shoe while the flash can be put somewhere else.
The simplest way to set flash exposure compensation with an auto flash is to “lie” to it about what aperture you're using. Cameras don't lie, so for Canon 580EX2 and Metz 54 MZ, you need to dial in the desired compensation by hand.
Manual
When a flash is in Manual mode, the power ratio to use for correct exposure is no longer determined by metering of reflected light, as it is in E-TTL and Auto modes. Instead, exposure is controlled by power ratio, aperture and guide number (GN).
Not all flashes let the user set a power ratio. In that case, assume that only a single power ratio (1/1) is available.
Unless you use a flash meter, exposure control in Manual mode is done by computing the aperture to use based upon ISO, distance from flash to subject, and the flash's GN. The GN is usually given for the full power of the flash for ISO 100, for either meters or feet. Note that if the flash has a zoom head, or a fresnel lens that may be used to focus the beam, the GN varies with the position of head or lens.
To work out the correct aperture at ISO 100 from the GN, simply divide the GN with the distance to the foreground subject, and set the nearest aperture.
For example, at ISO 100 for a flash with a GN of 40 (meters) at full power, and the main subject 7 meters away we get 40/7=5.7. We use the nearest available aperture, which is f/5.6.
If you are shooting at a different ISO value than 100, you mulitiply the guide number at ISO 100 with the square root of the ISO value divided by 100 to obtain a revised guide number. For instance, if the flash has a GN=40 at ISO 100, at ISO 200 the guide number becomes 40 x SQRT(200/100) = 57. If we still are 7 meters from our subject, we will use 57/7=8.1, and the nearest available aperture is f/8.
If the flash let you set a power ratio, the guide number is
reduced by the square root of the ratio you set. For
example a flash that at full power has a guide number equal to 100 has
at half power (power ratio 1/2) a guide number equal to
100 x SQRT(1/2) = 71.
When working with manual flash, most photographers use pre-computed tables that show what aperture to use at various distances and ISO-values. The image to the right show such a table. It is from the back of a Prinz Jupiter 2000 flash which has a guide number equal to 18 (meters) for ISO 100.
For bounce flash against a white ceiling, first compute the aperture by dividing the flash's guide number with the total distance the light has to travel (i.e the distance from the flash to the reflecting point in the ceiling, plus the distance from the reflecting point to the subject). Then open up at least two extra stops to compensate for light being absorbed by the ceiling. Check the histogram to determine if the exposure is correct, and adjust if necessary.
For fill flash, increase the shutter speed until the background is properly exposed. To lessen the effect of the flash on the foreground you may dial down the light output using a suitable power ratio, increase the subject to flash distance, or use light modifiers such as diffusers.
If you regularly shoot complex lighting setups with one or more manual flashes, you may want to invest in a handheld flash meter (e.g. Gossen Digiflash). With a flash meter, you start by metering a test flash with all your lights in place and set up with appropriate power ratios. You then read the aperture from the flash meter, set it on the camera, and proceed to take one or more exposures lit by the same flash arrangement. There is no need to make another reading until you rearrange the lights. A flash meter will work with a multiple flash setup, bounced flash, and all sorts of light modifiers (e.g. brollys and softboxes).
4. Off-camera Flash
To move the flash off-camera, you can use wires or a wireless setup. For a wireless solution, you can either use Canon's dedicated wireless sytem, or you can use a third party solution using wires, plain optical slaves, radio control, or a combination of all these. This section discusses the pros and cons of all the options.
For off-camera flash, Many cut down on the total cost by mixing radio, optical triggers and wires. They put a radio transmitter on the camera as master, and use this to trigger a few slaves strategically positioned units with a radio receiver. The light from these will then trigger other units fitted with optical receivers. Units in close proximity to each other are connected to the same optical or radio receiver by wires. By doing it this way, total cost is kept low, and at the same time the photographer can move around freely because no wires attach the lighting to the camera.
Dedicated Wired Flash
To move a single Speedlite off the camera, you can use the Canon Off Camera Shoe Cord 2 (OC-SC 2) or Off Camera Shoe Cord 3 (OC-E3). These are short (about 60 cm) coiled cords. The difference between them is that the OC-E3 has better seals against moisture than the OC-SC 2. These are just extension cords and preserves all flash functions including E‑TTL (i.e. the flash works like it has been mounted directly in the camera's hot-shoe). Their main use is for mounting a Speedlite flash on a flash bracket.
For multiple off-camera flashes, Canon used to offer a wired solution built around the Hot-Shoe Adaper 3 and the TTL distributor. This system, however, is not compatible with E-TTL. For digital cameras, Canon instead provides a sophisticated wireless system for controlling multiple off-camera Speedlites. This system is described in the next section.
Dedicated Wireless Slave Flash
To use wireless slave flashes with Canon's dedicated flash system, you may place an E-TTL-compatible master transmitter in the camera's hot-shoe. This master transmitter uses infrared (ST-E2) or visible (Speedlites and the Sigma 500/530 DG Super) light to control one or more slaves. The system is quite sophisticated, and lets the photographer select one of four channels (to minimize the risk of interference from other photographer's equipment), and to control flashes in several groups with different power ratios. Wireless slaves may also be fired in manual or vario-power modes.
To use Canon's dedicated flashes as wireless slaves you need to use a dedicated flash with the capability to act as “w/l master” (see the notes field in the table above), or you need to have Canon's dedicated wireless transmitter ST-E2 in the camera's hot-shoe. The camera's own pop-up flash can not be used to trigger Canon's dedicated flashes as wireless slaves.
Canon's wireless flash control system works well indoors. Outdoors, it requires a line of sight between the receiver and transmitter and is not reliable in bright sunlight. Note that the transmitter on the 550EX, 580EX and 580EX2 is part of the flash head, so this restricts positioning of the master. However, setting the unit to “master” will zoom out to give the signal an 80° coverage.
Optical Slave Triggers
Plain optical slaves still have their place. For instance, if you do not want to buy the dedicated ST-E2 wireless transmitter or EX Speedlite to control off-camera flash, you can use almost any old flash unit in a wireless slave setup. Some flashes even have a built-in optical slave trigger, such as the old SB-26 or Metz 44-MZ 2. Most studio strobes has a built in optical slave trigger. For generic flash units such as the Vivitar 285HV, you can buy the SL-2 remote flash trigger.
With plain optical slave triggers, you need to avoid or ignore the pre-flash. The pre-flash will ruin your shot by setting off the optical slaves before the shutter opens. How you do this is described in the next section).
If you don't want the master flash to contribute light to the exposure, dial down the power ratio as far as it will go without making your slave flash(es) unreliable. If you want to reduce the master flash output without affecting the range, you can make a makeshift IR-pass filter by taping black unexposed E6 slide film in front of the master flash.
There is of course no way to make E-TTL exposure control work with plain optical slave flash. In this kind of setup you must use the camera in manual (M) mode. Refer to the sections Auto and Manual to learn how to control exposure in these modes.
Note 1: You can not use your Canon DSLR's pop-up flash to trigger simple optical slave flash receivers without taking fairly drastic measures (described in the next section) to disable E-TTL. You can get around this by ignoring the pop-up flash and instead use a Canon Speedlite in manual mode, or an auto or manual flash, in the hotshoe.
Note 2: Several newer flashes, including those from Canon, do not work well with some third party slave receivers such as the popular Wein HS slave receiver. The flash will fire, but only once. The flash need to be power-cycled before it will fire again. The reason for is that the complex electronic circuits in these newer flashes prevents the Silicon Controlled Rectifer (SCR) used in most slave receivers from resetting.
Disabling pre-flash
Using plain optical slaves (i.e. a setup where the flash on the camera is used as master to trigger one or more slave receivers that are programmed to fire when they see the light from the camera flash) on an advanced Canon camera is not straightforward..
The problem is that the E-TTL pre-flash that is at the core of Canon's flash system will trigger the optical slave, thus making the slave flash unready for the actual flash. Some Canon DSLRs also strobes the on-camera flash as AF-assist light, and this will also trigger the optical slave. To turn this off, you need to turn off E-TTL, and you may also need to disable AF-assist. Turning off AF-assist is described in the custom function section in the manual for the relevant cameras.
To turn off E-TTL for Canon compacts, such as the Powershot G5, use manual mode (M). See p. 101 in the Powershot G5 manual for details.
As far as I know, there is no straightforward way to disable E-TTL for the built-in flash of Canon DSLRs (but check your manual, I may have missed something), but several methods exist that have the same effect:
- Attach an external flash unit to the hot-shoe. You can either use a cheap non-Canon flash, or you can use a Canon Speedlite set to manual. Most Speedlites (the Canon 220EX and 420EX are exceptions) have these modes.
- Attach an external flash to the camera's pc-connector instead of from the hot-shoe. Most flashes (the Sigma 500/530 DG ST is an excepetion) can be triggered from the pc-connector. To use this method, both camera and flash must have the appropriate connector, or you need an adapter.
- Use isolation tape to cover the extra E-TTL contacts in the hot-shoe.
- Use a method known as “blank FEL”.
Here is the receipe for “blank FEL”:
- Make sure the built-in E-TTL flash is popped up and ready.
- Cover the flash completely (e.g. with your hand, tin foil, or a dark cloth).
- Push and release the Flash Exposure Lock (FEL) button. The E-TTL preflash will be emitted, but should not trigger the slave strobes.
- You now have 16 seconds to shoot your picture.
- Uncover the flash, and depress the shutter button fully to take the picture.
For more details, and some variations, see Julian Loke's note on blank FEL.
Radio Slave Triggers
Optical solutions for off-camera flash of both the dedicated and plain variety struggles outdoors, especially in bright light. Optical units also require a clear line of sight between master and slave.
For this reason, many instead opt for radio transitters to control off-camera flash units. Radio will work outdoors in bright light, and requires no line of sight between master and slave. It also avoids the problem, noted above that not all optical receivers are compatible with modern Speedlites.
The downside of radio is cost. Quality radio systems, (e.g. Pocketwizards), are expensive, but in later years, several low cost alterantives have become available.
With one exception (see below) there is currently no way to make TTL exposure control work with radio triggered slave flash. In this kind of setup you must use the camera in manual (M) mode. Refer to the sections on Auto and Manual to learn how to control exposure in these modes.
A company known as radiopopper provides a hybrid solution that lets you use optical TTL exposure control by means of radio. To make it work, you put your master Canon speedlite (e.g. a 550EX2) in the hotshoe, and attach a radiopopper radio transmitter to this with Velcro. Then you take a radiopopper receiver and Velcro it to a remote speedlite, and you use a bendable fiber optic cable that goes into from the receiver and into the remote speedlite's optical sensor.
Off-camera flash caveats
Some newer Canon Speedlites, in particular 430EX and 580EX, fire at random with some versions of the Gadget Infinity radio triggers. The problem is fixed in a later model. Check out compatibility with your Speedlite before buying if you use one of these. There is some discussion about this in this thread on Flickr. It is long, but look for entries from RAitch between 201 and 300 (on page 3). Older Speedlites, like the 550EX and 420EX, do not have this problem.
The Sigma 500/530 DG Super must be set to C0 SL mode (that is the normal slave mode) to be fired from a simple two-contact hot-shoe that is featured on most optical and radio triggers. It will not fire at all in manual mode without a full E-TTL connection to the camera body. It can't be set to FP (high speed sync) or second curtain sync in C0 SL mode.
The Sigma EF-500/530 DG ST does not have a slave mode, and can not be used as a slave flash
5. Choosing a Flash
What type of flash should you buy? Below is some points to help you decide, but only you know your requirements.
Dedicated E-TTL flashes are made to work with your Canon camera, and the top-of-line models allow for wireless control using multiple flashes where some may be inside softboxes, or used in other complex lighting arrangements. If you want to use low intensity fill flash, then you probably want E-TTL. Auto flashes in general can not be set to very low power for low light fill, and manual flashes with variable power ratios require the use of a separate flash meter or cumbersome guide-number calculations.
The downside of Canon's dedicated E-TTL flashes is cost. They may cost more than three times as much generic flashes with equal power output. If you want a bright flash to be your main light, then you can save some money by choosing a generic auto flash. For instance, the dedicated Canon Speedlite 430EX2 (GN 32) carry a sticker price of around $330, almost equal or more powerful generic flash guns such as the Vivitar 285HV (GN 31) or Sunpak 383 Super (GN 35) will cost only about $70-100 brand new, and used models can be had for a lot less than that.
The E-TTL system provides a fully automatic exposure control that seamlessly integrates camera and flash, but the pre-flash sequence also introduces a tiny shutter delay. For instant response (e.g. skateboard photography), you may be better using a dedicated flash that also gives the option of using a non-TTL mode such a manual or non-TTL auto, or just use cheap generic flash units.
There is also third party dedicated flashes from Metz, Quantum, Sigma, and others. Currently, I know little about the compatibility and quality of these units, so if you consider one of these, make sure you check it out is the store before committing to a purchase.
Power matters. Whether you choose a dedicated or generic flash, if you intend to use bounce flash, I would not recommend a unit with less power than the Canon 430EX2 (GN 105ft/32m) or a Vivitar 285HV (GN 120ft/37m). Be warned that the Canon 430EX2 can only be bounced in small rooms with a low, white ceiling. Depending upon imager sensitivity, room size, distance to ceiling, ceiling whiteness, etc. you may need even more power than the Canon 430EX2 affords to get good results with bounce flash.
Manual flashes are going out of fashion, and while stock remains, they can be picked up from bargain bins for next to nothing. A number of perfectly working manual flash guns can be had for small change at eBay and garage sales. If you learn how to use a manual flash, you may save a lot of money by being able a reuse any old flash gun you may have left over from your film days, or a cheap generic flash you may buy at a sale. If you buy an inexpensive handheld flash meter, you'll have no trouble getting the right exposure, even in complex situations involving fill light or multiple flashes. If you don't want to buy a flash meter, you should be able to pick the correct aperture for a manual flash from tables of guide numbers and subject distance. This may sound awkward, but it is not difficult after you've gotten used to it.
However, if the manual flash have no variable power setting, your options for controlling the light will be limited. Also, metering a test flash, or using guide-number tables may slow down your action. If you don't want to go through these steps, make sure you buy an E-TTL capable dedicated flash or a auto flash.
Canon E/EG/EZ/ML/TL-series vs. EX
Canon's older series of Speedlites have used various suffixes (E, EG, EZ, ML, TL) after the model designation. While the names of some of these are very similar to modern Speedlites (i.e. “430EZ” vs. “430EX”), the older series flashes are not compatible with modern Canon digital cameras.
Canon offers the following advisory on the use of Canon Speedlites other than the EX-series in the User's Manual for the EOS 400D/Rebel XTi:
“The flash cannot be fired with an EZ/E/EG/ML/TL-series Speedlite set in the TTL or A-TTL autoflash mode. Use the Speedlite's manual flash mode instead if provided.”
However, this is often not suffiscient. Some non-EX-series Speedlites will not fire if placed in the hot-shoe of a Canon EOS digital camera, even when set to manual flash mode. They can, however, be pressed into service with a pc-connector/adaptor, or a slave receiver. To use it directly in the camera's hot-shoe,you can put insulating tape over the “extra” pins, exposing only the center pin and edge connector.
If you can get it to fire, a non-EX-series flash will operate in manual mode only on a modern camera.
If you already own an old Speedlite, it may be worth a try, but I do not recommend buying non-EX-series Speedlites for use with Canon digital cameras.
The same goes for third party dedicated flash guns that is not E-TTL compatible (e.g. Sunpak 355 AF TTL).
TTL-support and older cameras
Most older Canon film-based EOS bodies does not support E-TTL (there are some exceptions, such as the Elan II/EOS 50, so check the manual for the particular model you are intersted in). Instead they control the flash by having an internal sensor that measures flash light reflected off the film during exposure, and uses this data to switch off the flash when just enough light has reached the film. This mode of measurement is sometimes called OTF TTL (Off The Film Through The Lens).
All modern EX-series Speedlites, as well as the Sigma 500/530 DG Super, supports TTL mode. This means that you can buy these flash guns for use with older cameras as well as new.
Don't be confused if your camera's manual mention something called A-TTL. A-TTL was a small improvement that Canon introduced at one point. The improvement was to emit a series of pre-flashes when the shutter was half-pressed to compute optimal aperture in P-mode. However, in A-TTL actual flash output is measured by the OTF TTL sensor, just as it is with “plain” TTL, and “plain” TTL works fine with all cameras capable of A-TTL.
Flash trigger voltage
A matter of much debate is the maximum trigger voltage that is safe for a flash that is to be used in the hot-shoe on a Canon digital camera.
For connection through a pc-connector, Canon lists the maximum safe trigger voltage in the manual (e.g. 250 volts). However, this number does not apply to the hot-shoe. Canon does not officially give out information on the safe voltage for hot-shoe mounted flash guns (beyond the obvious recommendation that you should only mount one of the Canon's own Speedlites in the hot-shoe).
However, an email from Chuck Westfall (Director, Media & Customer Relationship, Canon USA), posted in this thread in DPreview's Canon EOS 350D/300D forum in April 2005 by Doug Kerr had the following to say about trigger voltages:
The EOS Digital Rebel XT [350D] uses a modified version of the EOS 20D's shutter unit. Consequently, acceptable trigger circuit voltage for both cameras is the same, i.e., 250 volts. Except for the original Digital Rebel [300D], all current EOS digital SLRs (i.e., EOS-1Ds Mark II, EOS-1D Mark II, EOS 20D and EOS Digital Rebel XT) generate their X-sync signals electronically rather than mechanically. This is why they have higher acceptable trigger circuit voltage ratings than earlier models like the D30, D60, 10D and original Digital Rebel [300D]. These older models cannot be modified to achieve a higher trigger circuit voltage rating, since such a modification would require a different shutter mechanism as well as a complete redesign of the supporting circuitry.
I take this to mean that all Canons DSLRs newer than the 350D, as well as all the professional models, can use flash with trigger voltages up to 250 volts in their hot-shoe. However, 6 volts is the safe limit for the D30, D60, 10D and 300D.
IMPORTANT DISCLAIMER: The above information is believed to be genuine and is reported here in good faith. However, I disclaim any responsibilty for your camera if you hook it up with an oddball flash gun and it fries. If you choose to act on this information, you do so at your own risk.
CAUTION: To avoid doing harm to the camera, you should always measure the trigger voltage before using a non-E-TTL flashes on a Canon digital camera to make sure they are within safe limits. Some flashes, and in particular vintage editions of the popular Vivitars, may have very high trigger voltages and can damage the camera. (The new ones, e.g. the Vivitar 285HV, use 6 volts and is «safe».)
As for technical protection measures, Wein sells a range of devices (safe-syncs) to protect against excessive trigger voltages, but in my opinion, using a radio slave. is a just as easy and more flexible.
For more information on flash trigger voltages, see this webpage.
Final remarks
If you intend to use several flashes in a wired or wireless setup, you need to think careful about your options. For a wired setup you're better off with flashes with a pc-connector (otherwise, you need to buy adapters as well). For a wireless setup, you need to decide whether you want to use Canon's dedicated wireless system, or to use third party devices built around optical or radio receivers. Not all flashes are compatible with all types of receiver, so if you build your wireless system from components from several sources, you need to make sure that the units are compatible before you buy.
When buying second hand, make sure: 1) That the flash you buy is compatible with your camera with respect to trigger voltage, electrical connections, and operational modes; 2) that the battery compartment is clean and the contacts free of corrosion; 3) that the body, including the foot, is mechanical sound and free of cracks; 4) that the recycle time is reasonable with fresh batteries; and, 5) that the colour temperature has not shifted (photograph a WhiBal-card or a neutral grey surface, locking the camera's white balance on “flash” and make sure that the RGB-values are reasonable neutral.
6. Link farm
- Canon:
- EOS Speedlite Tips (Audio commentary by Stephen Wilkes on general flash use, while George Lepp discusses macro flash photography.)
- Canon:
- Flash Exposure Lock and Compensation
(Short turorial on using FEL, FEC and FEB)
- Chuck Gardner:
- The Canon EX Flash System (Introduction to use of wireless power ratios and more.)
- David Hobby:
- Strobist
(Great blog about flash use and lightning in general by Balitimore based photojournalist David Hobby.)
- David Hobby:
- Strobist: Lighting 101
(Good tutorial on using off-camera flash.)
- David Hobby:
- Strobist: On assignment
(Examples of clever use of off-camera flash.)
- N.K. Guy:
- Flash Photography with Canon EOS Cameras (More than you ever wanted to know about EOS flash.)
- David J. Herzstein:
- Canon EOS Speedlites Comparison Table
(Huge table covering most Speedlite features)
- Vincent Laforet:
- Show Me the Light: Lighting with the Canon 550EX flashes (Photojournalist on wireless E-TTL on location.)
- Edwin Leong:
- Flash, Flash technical (Basic tutorial on flash photography.)
- Neil van Niekerk:
- Flash Techniques, (Tutorial on flash photography for weddings and portraits.)
- Vinicius Matangrano:
- How to turn the 380EX into a Manual-mode or a TTL-only flash unit (Details on E-TTL flash contact layout.)
- Ralph Paonessa:
- Quantum Turbo batteries: Supercharge your flash
(Using Quantum battery packs on a canon 550EX Speedlite)
- Ralph Paonessa:
- High Speed Sync for flash at any shutter speed
(Introduction to FP flash use for Canon and Nikon)
- Daniel Rocha:
- Flash Work
(18 part tutorial on EOS flash)
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