I recently upgraded my system from a Nikon Coolpix 7900/WP-CP4 housing and Inon 105AD lens to an Olympus Stylus Tough 8010 camera and PT-048 housing. I'm very happy with the new camera and housing, but had a bear of time finding a suitable wide angle lens, largely because I did not want to have vignetting (I also understand now that vigneeting is a problem for many 28mm equivalent cameras).
As I began my search for a lens, I soon found out that there are not good solutions for wide angle wet mount accessory lenses that will avoid vignetting with a digital camera with the equivalence of a 28mm native lens. My first hope was an Inon UWL-100 28AD lens - I like Inon lenses - however, this lens resulted in relatively more vignetting for this camera and housing than I wanted. Note that I had to use an Inon base mount for a PT-047 housing because they had not yet released one for a PT-048 housing, which seemd to fit properly and work but may not have been the optimal mount for this lens and this housing. This lens was identified for 28mm equivalent cameras, so I had high hopes that just did not pan out.
I had good success with a Fantasea Bigeye 67mm lens. This is basically a dome port for your camera's native lens. It worked very well, and saved me on a dive trip to Palau and then Truk Lagoon because it allowed me to take some outstanding photos with really great clarity that I could not have achieved without some sort of wide angle lens. The primary down side for me was that you can't zoom with it. This lens also requires that you set the camera to macro (I assume because you are focusing on a virtual image created by the dome port), but this is not a down side because the angle of view is very, very wide, the optics are great, depth of field is great, and it took really nice photos. It is a plastic lens, and this makes it very light. There was no vignetting. There may have been some cases where it would have been better to set the 8010 to its supermacro mode when using this lens. However, the 8010 supermacro mode prevents the use of a flash, and therefore, prevents use of an external strobe as well. This may be unique to the 8010 camera.
I decided that I wanted the greater flexibility to zoom with the lens attached, so I started my search for a traditional lens, preferably glass, that would not vignette. I only found one, which was an Olympus PTWC-01 lens with 67mm threaded mount. The back glass on this lens is 50mm. I was able to borrow a friend's lens and test it - it did not vignette in the water. Unfortunately, this is an older lens that may be out of production, and it is difficult to find. It is also very, very big and heavy. I found some on the internet for sale, but decided against it - my goal in UW photography is to go smaller and lighter to the extent possible.
I then found a wetpixel forum discussion that mentioned the Inon UWL-100 67mm thread mount lens (Type II). It mentioned that the back glass on the lens was 43mm, which is wider than the native lens on my camera, so I tried it. It worked very well for me, but produced some vignetting. I decided I could live with this amount of vignetting and have gone with this lens (there is no vignetting when shooting video). I learned a few tricks with this system that I'll share: 1) the zoom on the camera is not easy to control, but one to three clicks of the zoom seems to eliminate the vignetting; 2) the camera forces a zoom to a fixed level when you switch to Supermacro. That zoom level stays put when you switch back to either normal or standard macro modes. Therefore, you can effectively set a fixed zoom by first going to supermacro, and then to either standard macro or normal modes. Note that if you zoom around in supermacro before switching to the other modes, you will not acheive the standardization of the zoom.
I'd like to know if anyone else has had success with other lenses, either with an 8010 camera or with other 28mm equivalent cameras, especially in avoiding vignetting. I had checked into a Fisheye Fix UWL-04 lens and had high hopes for it. The folks at Fisheye Japan commented to me that it was designed for a 28mm equivalent lens camera and thought it might avoid vignetting. Unfortuantely, I couldn't find anyone who had this lens available when I was checking, so I can't confirm or deny this. If anyone has experience using this lens with a 28mm equivalent camera, I'd like to know if it vignetted or not.
It seems to me that the Ikelite W-20 67mm mount lens may be similar to the Inon lens, but I'm not sure. If it has a back glass smaller than 43mm across, I suspect it would vignette more than the Inon, but if it is the same or larger, it may provide the same or less vignetting. Does anyone know the diameter of the back glass on the W-20 67mm mount? Has anyone tried this on a 28mm equivalent camera?
There seems to be a gap out there from the lens manufacturers when it comes to accessory underwater lenses for 28mm equivalent cameras, and new lenses to avoid vignetting don't seem to be in production. Perhaps there will be new models that avoid the vignetting once the current economic climate takes an upswing.