What is "normal" lens for UW?

[pinstripe1]

As I remember it, above the surface 50mm is a 'normal' lens, ie has the same field of vision as the human eye. I have heard that UW the equivalent would be 35mm.

Is this true? If so, why the difference? I assume it has something to do with the refraction of water being different from air but my physics is rather rusty these days.

In addition to satisfying my general curiosity, this will help me narrow my camera lusts.

Thanks!

 

[luvdiving]

It depends. What camera setup do you have? I have the best overall luck with a 28 to 80mm zoom for a housed camera.:boom:

 

[scorpionfish]

Hi,

Due to refraction the u/w equivalent of a 50mm lens is a 35mm lens. However, u/w photography is a much different animal than its terrestrial equivalent. Here the main issue is depth of field. If you are using a camera like a Nikonos that requires that you estimate distance to subject, depth of field is extremely important--if you consider your subject being in focus important.

So, most u/w photographers chose to use a 28mm for a Nikonos as the longest focal length on the camera. I prefer the 20mm and sometimes use a 15mm. I guess I could have reproduced the depth of field charts to demonstrate, but I am not that speedy a typist--sorry. At any rate, the 15mm at reasonable f/stops focuses from about 1 ft to infinity!

Now, the "other" problem raises it ugly head: the shorter the focal length the more scenary you take in. That can be a problem if you are using strobes because they might not be able to give you coverage. It can also be a problem if you want to fill the photo with your subject and said subject is 5 inches long!

So, the short answer to the question is: give the 28mm or the 20mm a shot.

Now, if you have a housed camera (read lots of $$$$$$$$), you can use any lens you want because you get to focus it! My two favorites are:

(1) The 60mm micro that lets you do nice medium sized subjects to really small ones,

(2) and the 35-70mm zoom that lets you do everything from spreads of gorgonians to diminuative Hawaiin puffers.

Hope this helps,

Scorpionfish

 

[pinstripe1]

Many thanks! Most informative.