Needed Someone experienced in Aqualens

[radarguy]

has anyone got any "successful" experience in using an Aqualens? I got one new and afer flooding my camera in one foot of water I am ready to try and calibrate it again. But I have not been successful in about 3 or 4 rolls. I think I understand the concept of the virtual image but I don't know how to find it and if I did I don't know how to use it. I tried taking pictures in my pool of a target at a fixed distance and varying the focus but I seem to just get a lot of out of focus images. I have a Nikonos(newly replaced and rebuilt) and a 18mm Sigma with gears. I also wand to be able to do surface split screen shots. I am going to Hawaii this June and would like to have the technique down pat. Any suggestions would be greatly apreciated.
thanks,
Russ

AOL handle is reefdweller

 

[fdog]

It's been my experience that the published distances for the virtual image are surprisingly correct. IIRC it's 12 inches for the small dome and 0.4m for the 8" dome.

These have been spot-on for me. Actually the 8" has an infinity focus of about 0.41m for me with a 20mm f 2.8 .

For me, the Aqualens has been a specialty item. The hassle of using it is actually more than a housing. Regardless, it's been pretty simple to use:

Detach AI prongs.
Attach focus and Aperture gears.
Attach lens to Aqualens F-bayonet.
Check gear operation.
Set focus to 12". Twist external collar to theta symbol.
Adjust aperture gear and external collar so they match.
Lube, clean and attach dome.
Lube, clean and attach lens to Nikonos.
Attach anti-twist prong to shoe on top of Nikonos.

Slip ever-so-gently into water. The lever arm on this assembly is huge, and you can easily flood the whole works with a minor tilt of the Aqualens in relation to the Nikonos body. So I treat the whole assembly like eggs.

As for focus, it's pretty simple: keep your focus at the theta mark or closer. You can easily look into the dome to see what the lens is set at. Lens at 12" is the same as underwater infinity. So for the standard wide-angle at a range of 3' to 4', you might be focused at, say, 9" as indicated on the lens.

Your "working range", as indicated on the lens, is from 12" or closer. How close? It's a trial and error thing.

I've always found that I shy towards the slowest shutter speeds possible, just to give a bigger depth of field to compensate for my focus mistakes.

Hope this helps!

All the best, James

 

[radarguy]

Thanks, James.
Your description is pretty much like I figured. I guess the reason that I am confused is if the lens is set to 12" for, say, a 4 foot subject and your lens is half in and half out of the water, how can you focus on a boat or a beach? Will stopping down all the way really take care of that difference? Plus with most lenses, stopping down ALL the way usually degrades the focus somewhat.
Russ

 

[fdog]

I have to admit I've never used the Aqualens for over/unders, since they are sooo much easier to compose with a housed SLR.

Anyway, there's two issues: about 2 to 3 stops of exposure difference between topside and underwater (depending on water clarity and position of the sun in the sky), and, focus.

Focus is the easy part. Set the lens for close hyperfocal. Do this by using (for example) f22. Using the little orange depth-of-field tick marks, align 1’ mark with the right hand tick mark (or a little closer). You then look at the other orange tick mark to tell you how close your above-water objects can be.

As I recall, I could only get this to work with a 20mm lens behind an 8” dome port. A 6” dome port with a 20mm would only have objects out to a couple of feet in focus.

Using a 28mm, depth of field is so small (relatively speaking) that using a 6” dome, you might have something above water a foot away in focus, and with an 8” dome, maybe a couple of feet.

Using a 16mm Fisheye, the depth of field is huge, although it will take some stylish composition to hide the fisheye effect from the above-water portion.

My preference is for rectilinear when it comes to over/unders, because the human eye really notices fisheye when it comes to the above-water portion. If this is the same for you, you would be forced into a 20mm (great lens) behind an 8” dome. The Aqualens will easily accept an older screw-thread 8” dome, although they are not to be found anywhere now. Blame Ikelite.

This whole thing with depth of field and hyperfocal can be mostly avoided by using a split diopter. This is a conventional diopter that has been split in half, so the bottom of the lens looks through diopter, and the top half, through no diopter. These are pretty expensive, if you can even find them. Maybe about $120.

As an example, attached is a 20mm f2.8 lens set for hyperfocal behind an 8” dome port (virtual image at 0.4 meters).

All the best, James

 

[radarguy]

Well, I have a 6" dome with an 18mm lens. Am I spitting in the wind here or do you think a split image be a possible?
Thanks,
Russ

 

[fdog]

As a SWAG (Scientific Wild-***** Guess) I would think you should be able to get topside objects in focus out to about 5'. At f22.

All the best, James