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Re: Light Meters

David wrote:

Yes Ivo and they are called One Degree digital spotmeters. I've been using
one for years with my large format work and  for double checking the
calibration of the metering of my F4 and  other systems. Not cheap these
days. A  decent one will cost anywhere from $200.00 on up. ANd a good one
will meter such a small increment as you cited  but B & W film latitude is
rather forgiving.

I reply:

I have a few problems with using a spot meter for measuring light
intensities at the bottom of the tank. For one thing, I don't see how I can
use one in my tank without lifting the hood. The light fixtures are attached
to the hood and are very close to the water. The other problem is that the
light that I would be measuring would have travelled from the lights through
the water surface down to the object on the bottom of the tank and back up
to the spot meter. That is twice far as from the lamp fixture to the bottom
of the tank. In addition, I have a feeling that if you put a flat object on
the bottom of the tank it would not gather light from diffuse low angle
light very well even though that type of light is perfectly usable to
aquatic plants. Maybe if the object were a hemisphere and the spot meter and
the hemisphere filled the spot meters field of view then you would get a
correct reading for diffuse light. That is why I thought it might be a good
idea to get a cosine corrected light meter. The light from all angles would
be treated equally.