Underwater photographers often seek to take images of creatures that are simply too small to fill a frame at “normal” macro magnifications. Hence they have sought ways to add magnification via the use of additional magnifying lenses, or diopters that allow lenses to focus closer. For photographers equipped with SLR cameras, there is the option of adding a magnifier to the lens, which is optically the best choice, but this them limits the photographers choice of potential subjects.
Many housing manufacturers are now equipping their ports with a screw thread (often 67mm) that allows for the direct attachment of a “wet” lens externally. This offers more versatility as the lens can be added and removed during the dive. For those whose ports do not offer this, French accessory manufacturer Dyron has begun to produce adaptors that can be fitted externally onto the port, and which then allow the attachment of a 77 mm threaded wet lens.
The adaptors are made of POM-H Delrin, and are machined to a tight tolerance around the port. In addition, an internal groove in the adaptor holds a fine o-ring that seats the adaptor firmly. I could detect no motion or movement in the adaptor once installed. They are supplied with a leash, to ensure that the adaptor isn’t lost should it come unseated, but as the fit is so precise, this was never an issue.
Dyron supply an M77 double element macro lens, although it is also possible to use other M77 threaded lenses, or step up/down adaptors with lenses of differing sizes. The threads in the lens/adaptor have a very fine pitch, and although cross-threading it is unlikely unless significant force is used, the lens must be carefully oriented before the threads will engage. Dual-element lenses consist of two lenses cemented together. This controls chromatic and spherical aberrations (color and image distortion). The Dyron lenses also have a UV and anti-reflection coatings. For underwater use, where we have a myriad of image quality loss mechanisms at work that we cannot control, lens quality is an important criteria.
The Double Macro M77 provides +7 magnification at a focal length of 165 mm. They have a male and female thread, so can be stacked to provide greater magnification. In addition, they are delivered with an M67 step-down ring.
In use, the adaptor and lens were simple to use. The lens is small enough to be pushed up a wetsuit sleeve when not in use, although some may prefer some form of M77 holder on the camera rig. As you would expect, the additional magnification did tend to befuddle the auto focus (AF) and make it hunt, so I found that it was simpler to lock it off at a known distance, and then simply vary the distance to the subject by rocking in and out to achieve sharp images.
Again, as is to be expected, the lens limits the ability of the lens to focus at distance.
I found that the image quality using the lens to be very good. During the testing, my lens choice was a Nikkor 105mm f2.8 VR on a Nikon D7000 SLR. I was using Subal macro ports and the Dyron 77mm Subal adaptor.
The above crop shows that the wet lens is capable of pretty clean images at significant magnifications, with little chromatic or spherical aberrations.
The second image illustrates both the magnification possible, and the close-focusing ability.
Once again illustrating the close-up potential.
The sharp lines on this image show the lenses lack of spherical distortion. Straight lines are relatively rare in the natural world, but the edges of this image are quite remarkably clean.
This image represents the limit in subject size and distance possible with the lens in place. Of course, the lens can be removed during the dive if larger or more distant subjects present themselves.
I found that the combination of M77 adaptor and wet lens provided a new level of versatility to my photography. It is telling that once I had installed the adaptor onto the port, I did not remove it until the trip was over, and that I carried the lens on each dive. Although I had a Canon 500D and Nikon 5T diopters with me, I didn’t use them at all. From an image quality standpoint, I found the lens to deliver excellent results.
Many thanks to Dyron for providing the lenses and adaptors used in this review. Dyron currently provide M77 adaptors for Subal (two sizes for different ports), Ikelite, Seacam and Hugyfot macro ports. The Double Macro M77 lens retails at $220.95, while the adaptors retail for $99.95 each. For more details, please see the Dyron website.