I am not qualified to provide an in-depth technical review of camera lenses. But two interesting and relatively recent expansions of the UW photographers toolkit seemed interesting enough to discuss here. The first concerns a (relatively) new Nikon fish-eye zoom lens. The second the Nikon new mirrorless cameras in the FX (full-frame) format.
Fish eye-zoom Fisheye lenses in UW photography are superb lenses if you want to get really close to your primary target while keeping the background (e.g. the surface, other divers) in the same frame. Fish-eye lenses come in two versions: the fixed focus prime lens and the zoomed fish-eye. With the fish-eye zoom lens, you can change the focal length of the lens. It thus has the ability to take those forced perspective images at the shorter focal length or use a longer focal length to fill more of the frame. On a full-frame camera, it allows you to switch between frame-filling and circular fisheye. But the zoom lens is also useful to reduce its angle of coverage, for example, zooming in to fill your frame with a shark at a 2-meter distance, or with that small colorful fish at a 30-centimeter distance when using the CFWA technique.
A popular example is the Tokina AT-X 10–17mm f3.4-4.5 AF DX – a fisheye zoom lens designed for APS-C sensor cameras, which is also usable on full-frame cameras (see insert: top left). Then comes the newer (larger, heavier and more expensive) Nikon-8-15mm fisheye lens (see insert: top right) that according to some recent expert reviews seems to be a must tot full frame underwater photographers. The lens produces excellent sharp pictures, great colors and offers a circular image at 8mm (floating in a black background) as well as 180 deg diagonal view at 15 mm. The drawback might be that zooming in between 8mm and 15 mm, will show and cut off circle with black corners. A circular view is not everyone’s favorite, but It can offer spectacular artistic images, for example when taking over-under shots of a sunset above a coral reef.
This new lens can also be used on DX (cropped) sensors, like for example the Nikon D7200. On the zoom ring of Nikon 8-15 there is white marker placed at 11 mm, indicating that with a cropped format the lens will work in the range between 11 and 15 mm: at 11 mm it will produce a 180 diagonal view and at 15 mm a 110 deg diagonal view (which is about the same range as the Tokina 10-17). At lower values than 11 values, the image will show a cut off circle with black corners. This is because the DX sensor is 1.5 factor smaller than that of a full-frame FX camera. So 10mm and 15 mm a DX camera would be equivalent to 15 mm and 22 mm on a full-frame camera respectively. Will this lens also work in DSLR housings for cropped sensors that accommodate the Tokina 10-17? I think it should, with the specific right zoom gear and dome port. My preference has always been the 5-inch minidome, allowing you to get very close to your UW subject. A minidome is a half-spherical dome aligned with the nodal point of the lense.
The question, of course, is if the new lens is worth the big investment of around 1000 Euro. Some of us would say: only if it produces superior quality of pictures on a DX camera than the good old Tokina 10-17. The ‘Tok’ is a much cheaper fish eye that for many years has been the workhorse for most cropped camera fish-eye adepts. As one of those, I am really looking forward to some comparative tests of both lenses on a D7200/D7500 camera. But see: https://www.uwphotographyguide.com/content/first-impressions-nikon-8-15mm-fisheye-lens-review and https://wetpixel.com/articles/review-nikon-8-15-mm-f-3.5-4.5-fisheye-lens/P1
The advancement of the mirror-less cameras In the early days of mirrorless cameras, DSLRs simply did most things better. Mirrorless cameras were more compact and much cheaper, but that was it. Almost always, a DSLR could focus faster, shoot faster, had a much better viewfinder, and more often than not produced superior image quality. But with the increased quality of electronic viewfinders, the much smaller weight and size and the bigger sensors the mirrorless camera seems to be gaining ground on the DSLR cameras, which make them no longer simply a more compact (but not always cheaper) alternative.
Many UW photographers in the past including myself have been using the Nikon DSLR camera, either in the full-frame (FX) or cropped (DX) format. Nikon has been making some revolutionary changes by introducing the mirrorless Z6 (24megapixels) and Z7 (45 megapixels) full-frame cameras (see insert lower panel, to compare their size with the Nikon D850, explaining why the Z7 is also known as the 'mini D850'). When directly comparing the Z7 to the Nikon D850, the key drawbacks seem to be slower autofocus in low light settings, slightly less dynamic range, and shorter battery life. One of their best features is its high-resolution electronic viewfinder (EFV) making optical analog viewfinders (OVF) in DSLRs look ancient. While the OFV gives a view through the lens, the EFV gives you a view through the sensor and the option to present a lot of information. The LED screen serving as an additional option to view the live scene, prior to or after your shot. In an underwater housing, the EFV image may still benefit a lot from a 45-degree viewfinder on the back of the housing (see:https://www.backscatter.com/reviews/post/Nikon-Z7-&-Z6-Underwater-Camera-Review).
The Z mount has a larger diameter larger than the F-mount on the DSLR bodies and lies closer to the sensor because of the space saved by skipping the mirror. When combined with an FTZ adapter the Z will also take the new Nikon 8-15 fish-eye discussed above, and older DSLR lenses, even those from the DX (cropped sensor, APS-C) range. Unlike with the DSLR, the Z cameras will automatically apply a DX crop, so that the DX image always fills the finder. The latest AF-S (1984 - today) and AF-P lenses seem to work nicely. However, older DX lenses, like the 10.5mm fisheye will need a manual focus (according to the Ken Rockwell reviews). There are no tests yet of the performance of third-party fish-eye lenses, such as the Tokina.
Nikon has just brought out an even cheaper mirrorless APS-C (DX) camera called Z50 with an electronic viewfinder. Comparable to the D750 in resolution (20 megapixels), but smaller and lighter and with a Z mount. No UW housings are yet available for this model. To use your old DX lenses, you again need the FTZ adapter. So, Nikon will now be creating four separate lines of lenses: APS-C and full-frame for DSLR, and APS-C and full-frame for mirrorless cameras. So far, the big promise of the new mirrorless series is that they provide a lighter and smaller camera (allowing more compact housings, although the bigger lenses would mean an increase of weight and volume again) and a large bright electronic viewfinder, without losing much quality as compared with the DSLR full-frame Nikon workhorses. But some critics have argued that Z-50 is is a mistake since you are not able to profit from the larger Z-mount with a smaller sensor. And that it will create extra costs because one needs to buy new lenses or an adapter for your old DX (F mount) lenses.
What to choose will become much more difficult for UW shooters in the near future. Since the cost of full-frame sensors has decreased dramatically over the last few years a budget FX camera would compete head to head with a high-end DX camera