Auto Focus or manual?

jhaaja

Now I finally got my housing and did the first dive today with it. I had the lens on AF and had quite a lot of difficulties to get the focus locked.

Is it possivle to get sharp pictures if I just use the lens as manual focus and focus it to infinity?

The lens is Canon EF 15mm Fish eye and EOS350D camera.

JH

Johnny Christensen

I would leave it on AF. The manual focus works best when you have a reference like on the Nikonos with the distance setting from 30cm to infinity. You are going to be hard pressed to judge acurate focus thru the viewfinder.
And locking it on infinity will you give you less than optimum results.

A autofocus works by detecting a sharp line or contrast. When the lens searches back and forth, it will try to read when that line is as sharply defined as possible.
But if you are using multible focuspoints at the same time, it will get confused, Especially underwater in the typical viz of coldwaterdiving.
So switch the selector to single focuspoint mode, that will increase your succes. And always dive with a powerfull sharply focused light. That is your cameras best friend when in the typical lowlight - no contrast that we find all over the baltic sea.

In the beginning, start out by using the single focuspoint in the middle of the veiwfinder. Lock it on the subject, keep the shutter halfway depressed and compose your picture, then shoot. I have found that to be the quick and dirty fix when you have little time or when you have your mind occupied by other things at the same time.
Later on when you know your camera and housings controls by touch. Then start using the other focuspoints, but it will take longer time. At times it will seem as the controls have a mind of their own when you are trying to change focuspoints with cold and neopreneclad fingers.

When looking for the right spot to focus on, then remember that the depth of field for the particulate lens you are using, are distributed with about 1/3 in front of your subject and the rest behind the subject. That means when choosing your spot, you are often better of choosing one that is slightly more in the foreground. That way you will get the most out of your depth of field. Why waste precious sharpness, letting it go into the background, where the picture is going to be soft anyways from limited viz. Might as well put it to good use where there is a decent chance of a sharp image.

You have a good camera and by it being digital, you can get to a certain level in one year that used to take 4-5 years to get to, in the days of film.
Shoot, evaluate, correct, reshoot. Spend a lot of time analyzing your pictures on the computer afterwards, even the ones that did not come out tells you something important. They taught you a new way of not getting what you wanted. And that knowledge is also worth a lot, especially when you suddenly are presented with "the kodak moment" and are under time stress.

Good luck. It's expencive, but that's life.

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abowie

If you set it on f8 and 1m you'll get pretty much everything in focus.

Personally thought I'd persist with AF and work out how to get it to socus properly. often it's just unfamilarity with the equipment.

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jhaaja

Thanks for the info and tips!

I submitted the somehow decent photos to the gallery. Now I just want to get back in the water to practice

Photographer himself:



SilentGhost:





Stage tank:

Sutty

With a dome port my camera needs to be on its macro function to allow focusing on the close virtual image the port creates. I get variably out of focus images otherwise. Assuming you have a dome port its possible that you are only just able to focus close enough without switching to macro mode, so could have trouble locking focus on AF.

Neil

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PeteS

Dome port? Macro? Normally Dome ports work with wide angle and Macro lenses work with flat ports. I'm confused, so could you explain?

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jhaaja

I have a 6" dome port with the 15mm lens. My camera does not have a macro switch. If taht kind of switch exists it is allways on the lens itself, but the 15mm lens does not have macro mode.

Johnny Christensen

My guess is that Neil is refering to a compact camera. In order for the manufactures to produce a camera that can "do it all" they sometimes equip the camera with a close up or macro mode to give the build-in lens the biggest possible range.
That is not the case with a SLR camera, there you would match the lens with the subject you are shooting. i.e a dedicated macro lens for small stuff and a wideangle lens for scenic shots.

But he may have a point, you should check Ikelite spec's to see if they recomend a dioptre on the lens. For some domeport and lens combinations they require a closeup dioptre to work. Though I would be very surprised if that was availeble for a fisheye lens.
My experience with Nikon fisheyes both the old 16mm for filmcameras and the 10,5mm for digital, there it's not needed. I use 8 and 10 inch domeports, both in acrylic and optical glass ones.

If I use the 20mm F1,8 sigma, then a closeup dioptre is required.

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Sutty

Johnny is right in thinking that I have a "compact" camera (Canon G2).
The optics of a dome port mean that once immersed in water it produces a virtual image at a very short distance from the lens (I think its usually a only a few inches, but don't rely on this). It is this virtual image that the camera has to focus on. With my camera in order to focus so close you have to change to "macro" mode. If your camera cannot focus close enough you will have problems focusing.
One way around the problem (I haven't tried this) is supposed to be to add a close-up lens (dioptre) on the front of your lens (or on top of a wide-angle lens if this is what is fitted to match the port - this then enables your camera to focus close enough.

Hope that helps,
Neil

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jhaaja

In my case I think the problem with the focusing was due to the lack of light. We were inside a cave so no natural light was available.

I think I need to attach my 21W HID with the video reflector to the other flash arm that I do not own yet to get enough light to get the focus locked.