Cheap “wide angle” converters – just say “no”
People looking for a cheap wide angle lens for a compact or DSLR sometime stumble over cheap converter lenses sold at Amazon, eBay and elsewhere.
The type of lens I am talking about, is a secondary lens that you mount in front of the prime lens attached to the camera. Such converter lenses do not have a focal length. Instead, they are designated by a conversion factor (e.g. 0.42x). You multiply the focal length of the prime with the conversion factor to find the combined focal length of the prime and secondary lens. For instance, if your prime is a 18-55 mm zoom set to 18 mm, and the conversion factor is 0.42x, the combined focal length when the converter is attached to the prime is 18 mm x 0.42 = 7.56 mm.
This type of lens typically have a conversion factor equal to or less than 0.5x (e.g. 0.25x, 0.3x, 0.42x, 0.45x or 0.5x). Adorama sells one for around $40. They're frequently found at eBay (search eBay) between $18 and $80. Some webshops sell them for more than $100. They are labeled with miscellaneous brands (e.g. Bower, Cokin, Crystal Vision, Deitz, Digital Concepts, Digital Optics, HD Optics, Hi Tech Optics, Kenlock, Opteka, Pro Optic Deluxe, Phoenix, Platinium, Sakar, SteinZeiser, Titanium, TopBrand, Vitacon, Vivitar), but all seem to have similar construction and performance, and may be sourced from the same factory.
They are often said to have “autofocus“, but of course they don't focus at all. Since they just go in front of primary lens, autofocus depends on your prime. Their projection is neither rectilinear nor circular. But they do suffer from a bad case of barrel distortion. Because of this, sellers tend to use the word “fish-eye” in their description.
Finally, they frequently come with a rear element labeled “macro”. This element is usually a single +12.5 dioptre lens element that can be detached and used seperately for close-up photograpy. But with +12.5 dioptre the working distance is bound to be extremely short, so it is not really practical to use this for macro photography.
Most sellers also put up images taken with the lens in the description, but they are always tiny, even by web standards. I mailed one of the sellers and asked for full-resolution example pictures. What I got was pictures downsampled to 1 Mpx and still soft as a baby's bottom. They also showed vignetting, massive CA, flare and ghosting, and of course barrel distortion.
The Adorama product sheet for the Pro Optic 0.42x quotes extensively from a review in Popular Photography Jan. 2002, which gives the impression that the product is half decent. It is not. If all you want is a “fun” lens to play with, and only want to put some low resolution images with massive barrel distortion on the web, then this may be the thing for you. But if you think you are buying a real fisheye lens, forget it. In my opinion, these converters, even if you pay as little as $20, is a total waste of time and money. Just say “no”.
If you want a second opinion, here is links some user reports found at various websites, blogs and boards: