ChrisA
Contributor
Can anyone explain (in detail with numbers) the effect of a flat plate lens port in water? I'd like to know how to calculate the difference in focus and angle of view between above and below water.
The effect of a flat lens port in water
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louisianadiver
Contributor
ChrisA:
The effect is exactly the same as the mask in front of your eyes. There'll be about a 25% magnification, which means that an object 4' away will appear to the camera and be in focus if the camera is focused to 3'. If you're focusing your camera for a specific distance, such as for Nikonos or Motormarine cameras, shoot from the apparent distance rather than from the measured distance, because the camera "sees" exactly like you do underwater behind a flat port. -Clay
ReyeR
Guest
This is a good place to start for calculating the AOC: it's a article by Dave Knight from camerasunderwater.co.uk: http://www.camerasunderwater.co.uk/info/pages/AngleCov.html
f3nikon
Guest
Put your camera in its housing and stick it a bath tub full of water measure the distance of the subject and take the picture. Measure the same distance in air, take the picture and compare. 25% mag. sounds about right ie a Nikon 105mm marco would be a 130mm with a flat port underwater.
Regards
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