Wireless optical flash trigger
This note is written for those who have trouble getting a simple, external. optical wireless optical trigger, to work.
This note does not discuss dedicated wireless triggering systems, such as Nikon's AWL, or Canon's wireless E-TTL II system. Nor does it discuss the use of built-in optical wireless triggers, such as those you'll find on most low cost YongNuo flashes and almost all studio flashes.
But if you have a simple optical wireless flash trigger such as those featured in this article, and want to make use of it, here's the missing manual.
To trigger the wireless optical triggers, you'll need:
- A lead (or master) flash.
- At least one remote (or slave) flash.
- An optical trigger.
Below is a more detailed descriptions of all three components, and how to set them up for wireless shooting.
For a lead flash, you may use the camera's pop-up flash, provided it can be set to fully manual mode with absolutely no pre-flashes. On most cameras, it is as simple as setting manual mode in the camera's flash menu. If red-eye reduction is on, make sure that this is also turned off.
NB: The lead flash must not be set to commander or master mode in any shape or form. The lead flash must be set to ordinary manual mode where it just emits a single burst of light when you press the shutter button.
If there is no way to turn off the pop-up flash pre-flashes, you need to have a manual flash in the camera's hot-shoe. It can be a generic flash (e.g. the Vivitar 285HV, or a dedicated flash set to work in fully manual mode.
It is best to use a lead flash with varipower control, down to at least 1/16 power. This is to minimise the impact of the lead flash without having to add an ir pass-through filter in front of it.
For a remote flash, you can use a generic flash (e.g. Vivitar 285HV, or a dedicated flash set to manual mode.
You can fire multiple remote flashes from a single lead flash.
NB: If you use a dedicated flash as remote or slave flash, it must not be set to remote or slave mode in any shape or form. The remote flash must be set to ordinary manual mode.
Note that low cost flashes only have manual mode (so there is no need to set manual mode). Expensive, dedicated flashes offer a lot of modes. For non-dedicated wireless optical flash triggering you need to make sure the flash is in manual mode, because this is the only mode that works with simple optical triggers.
My collection of optical flash triggers is shown below:
Optical flash triggers are in most cases very simple devices. There are no batteries, no on/off switch, no knobs or dials. They are powered by the flash trigger current, and turns on automatically when connected to a flash.
Making the connections
Most optical triggers have a hot-shoe. You connect a camera flash to the trigger by putting it in the hot-shoe. Some triggers have a different connector (e.g. Wein Peanut), and you connect it to a camera flash or studio flash with a suitable cord. Some have both.
To set up the remote flash for triggering you put it in the hot-shoe of the trigger, or connect it to the trigger with a suitable flash cord.
Before testing, make sure that you use fresh batteries and that your flashes are in working order. Check that all flashes are operational by pressing the test button on back of the each flash, to verfify that it fires. Also make sure recycle times are reasonable (and replace batteris if they are not). The image on the left shows the test button on a Metz 54 MZ-4 flash. It is marked with a flash symbol and doubles as a ready light. Refer to the manual if you're unable to locate the test button on your flashes.
Set up your lead flash and one or more remote flashes as described in the previous section. Then test the whole setup. For testing, set ISO 200 and an aperture of f/16. Set the lead flash to a fairly low power ratio (e.g. 1/64). Set up the remote flashes to low power (e,g. 1/64) with the flash heads pointed towards the camera. Having the flash head visible makes it simple to verify that all flashes actually fires. Make a test exposure. Review the image, and verify that all the remotes fire.
If not all remotes fire, check your settings and connections, and if it still does not work, turn to the troubleshooting section below.
Testing is best done indoors, in dim surroundings, and at pretty close range. Reliability goes down outdoors, in bright surroundings, and at long distances. You may experiment with placement and distance later, but to verify that everything is set up correctly and works, do the initial testing in an environment that is well suited for optical triggering.
Using remote flashes
Remote flashes triggered by a lead flash can only be used in fully manual mode.
- You can see that remote flashes fire with your eye, but the flash in not visible on the test exposure.
- Your lead flash is set up to use pre-flash or red-eye reduction. Make sure you turn both off. For more about pre-flash, etc., see this note.
- Remote flash does not fire at all when lead flash fires.
- Check the connections. Make sure the remote flash is firmly seated in the hot-shoe of the trigger, and that all cords are in working order.
Make sure the flash and trigger is compatible.
Make sure the flash has not entered power-save mode.
What is optical triggering?
Optical triggering is when a device with a photocell sensitive to infrared light senses a flash of infrared light and closes a circuit that fires the flash connected to the trigger.
Optical triggers are triggered usually by the infrared component of the light flash from a standard xenon flash. As evident from the diagram below, a xenon flash tube has a fairly linear output in the range of visible light (400 nm to 700 nm), very similar to natural sunlight. But xenon also has a very powerful output in the near infrared region above 800 nm. This makes it well suited for using infrared light for triggering.
If the signal from the xenon tube is not filtered, both visible light and infrared light is emitted. But we are only interested in the infrared component of the lead flash burst, since it is this infrared component the optical triggers respond to.
Ir pass-through filter
To avoid the light from the lead flash to have an impact on the scene, you may want to put a ir pass-through filter in front of the lead flash. This is a filter that blocks visible light and lets infrared light pass through.
Nikon makes an ir pass-through filter in the shape of the SG-3IR IR panel. It will remove the visible component from your built-in flash (it looks like solid plastic, but it lets IR through). According to Nikon, it is made to fit the D70, D70s or D200. However, users of the D300 say it works fine, and it it will probably work on most Nikon's DSLRs (Exactly which models it fits, I do not know. Use the comment field below this article if you have any experience to contribute.)
However, if you are frugal you can make a makeshift IR-pass filter by taping black unexposed E6 developed slide film in front of the built-in flash. Black unexposed slide film is transparent to IR light, but blocks visible light. (Somebody wrote to me and said that instead of slide film, you could use material cut out out from an old floppy disk, as this material too is transparent to infrared light. So far, I have not been able to use this method successfully.)