Canon 17-85 with Aquatica Dome

Hello,

I just got my first real UW housing (used Ewa-Marine before) for my Canon 20D!

Aquatica A20 + 8" dome port + zoom gear 17707 + port extension 18453.

Anyone knows if I need a close-up diopter lens for this setup? How many diopters, +3 +4?

Aquatica web site does not say anything. And I did not get any reply to my email from their customer service.

Also what carrying solution would you recommend for this housing plus Ikelite DS-125 strobe?

I am thinking about Pelican Waterproof case but not sure what size would be right.

Can't wait to get my rig underwater!

Thank you,

ignati

You'll find some say yes and some say no, I had the exact set up a while back and did not use a diopter and found that lens and port were great, I also used the DS125's strobes, did you get the TTL built into it?

Sorry Ignati, but I never got your e-mail, the 17-85 doesn't require a diopter to focus on the virtual image, in some instance a +3 might be beneficial for really close-up.

The physic of underwater optic are fairly complex, when using a dome you create a virtual image that is projected a at close distance in front of said dome, for a 8" dome that distance is about 12 " in front of dome or 16" from your "film " plane, so for a lens to perform well you need to be able to focus at least to 16". That's 16" from the rear of your camera. That data is available on the lens manufacturer web site or is an easy test to do, just put an object 16" away and if you can focus on it you're good to go.

On the can of worm that are diopter, a dome as a negative diopter strength when immersed in the case of our 8" dome it is just about -3 so adding a +3 re establish the balance and your lens will then be focused a more or less infinity when looking at that virtual image. it also mean two thing, you will be able to focus on subject almost if not all the way to the surface of the dome, and secondly you can forget about split shot if you uses a diopter, since you loose the ability to focus at far away subject in air. But in your case I wouldn't worry at the last one the 17-85 will all of its quality is a poor lens for doing split shots.

Also in some combination the corner sharpness was improved by using a diopter.

FYI For those who own 6" port that diopter requirement would be +4.

So here you go, yes and no about your need for a diopter. My 2 cents worth, start without one and eventually get a +3 and try it out. Underwater photography becomes very case specific as you implicated yourself deeper into it and part of the reward OR deception from your future result will come from how you addressed your gear requirement. Thank god, there are fortunately many blank pages to be written on this fascinating subject. Who would have thought not too long ago that some photographer would get awesome result from stacking a fisheye on top of a tele converter, That used to be called heresy and punishable by keel hauling

Just a reminder the address is .ca not .com as in info@aquatica.ca its a common mistake, the .com was already taken at the time

Jean,

Thank you for such a detailed answer. I will give it a try without a +3 lens first.

kriptap - no, I do not have a TTL adapter built-in. I tried the housing and strobe above water and was able to get decent

light after some manipulation with the aperture and the strobe's power selector. I will see how it works underwater.

Ignati