Depth Of field.

Is there a formula or rule for finding out what f-stop is needed to achieve a depth of field? for example, I see a fish about 1 inch long, I shoot it head first, what stop would be needed to get all or most of the fish in focus? is there such a thing, does it depend on what lens you are shooting with. Thx

Hi Patrick,

There are several depth of field calculators online, here is one:

http://www.dofmaster.com/dofjs.html

Basically, DOF is a function of f-stop, camera-to-subject distance and focal lenght, so it all depends on the f-stop, how far you are from the subject and what lens you are using.

Luiz

Use the DOF-Preview button

Or when you don't have a DOF-preview button on your housing, or can't use a handheld PC underwater, use the indicator scale on your lens.

Brand new Nikkor lenses include a chart of DOF for all fstops and a range of subject to camera distances.

Problem is that those rules (and online calculators) don’t work for underwater shooting. When shooting thru a flat port the refraction (4/3 or 1.33) has to be applied into those calculations. It’s not difficult to do it. But it gets really complicated for dome ports. For example, EXIF data show somewhat two foot subject distance when I have shot an infinity subject (Dome acts like a reversed close up lens underwater).

I think the only lenses providing real underwater DOF markings are the Nikonos and Sea&Sea underwater lenses (15 or 20mm for example). Even the Nikonos 35mm lens does only provide topside distance markings as it is not a true underwater lens (just topside lens with flat glass in terms of optics).

Julian