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Under Water, Over Land
Tools & Techniques for Nature, Outdoors, Wildlife & Underwater Videography.

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Old November 26th, 2008, 02:21 AM   #16
Inner Circle
Join Date: Oct 2001
Location: Honolulu, HI
Posts: 2,053
Originally Posted by John Miller View Post
Setting your focus to a fixed 5ft will be a problem.

Assuming your camera housing has a flat lens port, you have to correct the focus by a factor of 1.333 to allow for the different refractive index of water vs. air.

If your camera housing has a domed lens port, then you typical set the focus on infinity.

Basically, you need to be able to control the focus somehow.....
With a flat port, the correction has to do with focal length and not focal plane. A wide lens will seem less wide with a flat port.

When using a dome port, a "virtual image" is created about 2 feet from the focal plane (depending on the dome port used) and you'll need to focus on that. Setting your lens to infinity will actually focus beyond that virtual image and you'll end up with everything out of focus.

Secondary Focal Point of a Dome Port
Dean Sensui
Exec Producer, Hawaii Goes Fishing
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Old November 27th, 2008, 08:29 PM   #17
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Join Date: Jun 2006
Location: Grand Rapids, MI
Posts: 218
Time flies

I forgot I even posted this almost two years ago now. Well, I ended up using about 30 seconds out of about 30 minutes of trial and error footage. I learned a lot and can say I would cut down on the wasted shots next time I get wet.

Dean, you been to Hilo? I used to live on lanikaula st, makai of the university. Loved it there, many lifelong friendships there.
always learning
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