5D Autofocus Underwater

I took my new underwater setup (Canon EOS 5D, Ikelite Housing, 24-85 lens, dome port, DS50 strobe) diving for the first time the other day in a swimming pool with my local dive club. The good news is it didn't flood :-)

The bad news was the camera had a *really* hard time focusing underwater. I'd hooked up the gear on the housing to control the zoom-ring on the lens, and was relying on the camera to autofocus.

In one-shot AF mode, the camera doesn't let you take a picture until the subject is in focus. Above water with the camera in the housing this works fine. Underwater, when asking the camera to focus, it just couldn't manage it. I was mostly trying to focus on other divers approx 2 metres away. Because it wasn't able to focus, it wouldn't take any photos. If I took it out of One-shot focus mode and put it in AI Servo, then it still tried to autofocus, but it let me take a photo as soon as I fully depress the shutter. This worked underwater (shots were taken, stobe fired etc.), however they were still of course all completely out of focus!

My question is, what is wrong with my setup that meant the camera couldn't autofocus underwater? After looking around on the net, and from my own guesswork, it could be any of the following:

- I need a +4 diopter filter on my lens

- I need a "spotlight" (permanently on light) shining on the subject to illuminate it whilst the camera is trying to focus. My DS50 does not have a spotlight on it.

- I need a wider lens (24-85 widest aperature is 3.5).

- Autofocus isn't going to work and I need to put the housing's gear on the focus ring rather than the zoom ring and manual focus before taking photo.

I really hope I don't have to resort to manual focus, because that's tricky enough to do well above water, let alone under! Also I'd lose the use of the zoom ring.

Any pointers would be greatly appreciated.

You don't necessarily need a +4 diopter, that is very strong, but you certainly need a diopter. You're described the classic symptoms. Underwater the camera won't focus because the dome port acts as a strong negative diopter.

What is the closest focus (in inches) that your lens can acheive?

Cheers

James

Add the +4 diopter, chances are your lens cannot focus on the virtual image created by the dome port.

s.

The closest it can focus (above water) seems to be around the 0.5m mark.

Is it definitely the diopter and not being caused by not having a "spotlight"? Do other people shoot with just the DS-50 strobe (and no spotlight) ok?

I experienced exactly the same problem with my Canon 350. The tests in the pool were almost all out of focus. I have a similar outfit, with the Ikelie housing and 8" dome port. I don't use a flash, just the Magic filter. I was really concerned about my first trip on the Easter weekend to the Florida Keys. It actually worked out fine. I believe that my problem was low light and camera shake. The pool was a private indoor pool, and the lighting was not the best.

Once in the open water, I set the shutter speed fairly fast, and the majority of the shots were fine. I was also careful to hold the camera steady.

Hope you problem turns out to be similar, as the end result was easy to fix.

you can check out some of my shots from the weekend at:

http://www.gordalder.com/Vacations/Florida...2006/index.html

Gord

I was using the Canon 10-20mm zoom lens

What the "Magic" filter?

Nice pics.

Greg

Thanks, Pics are OK for my first try with the new equipment. Some were over cropped, and some slightly out of focus.

When I upgraded my camera and housing I decided to purchase the 10-20 zoom rather than the flash setup. I discovered the Magic filer and am now converted. Lighter to travel with, and easier to handle the rig underwater without the flash.

Leave your flash at home!

http://www.magic-filters.com

I will be posting some questions about my methods of using the filter. I didn't exactly follow the instructions. I was lazy, just "Auto fixed" my JPG photos, with out setting the white balance as suggested by the manufacturer.

All of my shots were in about 20 - 25ft of water, no flash.

Gord

Yes, a Diopter will fix the focusing issue. You will need a diopter on any lens that will not focus closer than 12 inches.

But the real question is why are you using a cheapo zoom lens on a $3000 body?

You will get much better results with a Rebel and $2000 of lenses than with a $3000 body and and a $300 zoom.

Ok, I'll order the diopter.

I'm aware the lens doesn't do the body full justice, but I can only buy one thing at a time, and I thought given the housing locks you into one particular body, it'll be more worthwhile to push the boat out a little on the body first, and I can buy better lenses later. I'd love to swap it for the 24-105, and maybe I will later in the year!

I also have a 17-40L, but I thought the 24-85 would give me a better zoom coverage. Perhaps you disagree on that choice (if so, don't be too hard on me - I am new to this field of photography!)? Perhaps the 17-40 will also work in the same port and I can try that sometime...

Greg

Greg - go with the 17-40L idf you can and simply get close to your subjects to fill the frame - tere will be less water between the subject and the lens and thius less color loss and less particulates = better picture quality. Most of the upper range in zoom is worthless underwater - you do not want to zoom to get closer to things - you have to work and get in close for a good picture...Best of luck...

cheers!

- MP

Yeah, I've read that. But past experience of me trying to get closer to fish / rays / sharks ends up with them swimming away faster than I'm approaching them :-)

Thanks for the advice though, the 17-40 should also fit in my port, so I can give that a go. Do people think I'll need a +4 diopter on that lens too?

Yes, the 17-40 is a much better choice. And it focuses to 11 inches so NO it should not require a diopter to focus though some people would recomend you use one anyway.

WARNING: do not get the 24-105 expecting to use it underwater. Due to it's diameter this lens will NOT fit in any ikelite port. Great lens for surface shooting, but not underwater.

If you are looking for a lens with longer focal length than the 17-40 you want to look at either the 50 or 100mm macro lenses.