Re: Finding camera leaks

[P3D Gregory J. Wageman <gjw@xxxxxxxxxx>]

Greg E. writes:

>  My response was that unless you had a very bright bulb it
>won't reproduce the "camera leaking while out in the sun for
>an hour" test. What fraction of the sun's light has to leak
>into your camera to partially fog 100 speed film (not fogged
>totally clear) in an hour. Is it 0.1% 0.01% or even less?
>
>  And could your eyes see that small fraction of light leaking
>out of your camera, coming from a small bulb (even a 2W
>halogen)?

I don't know for sure either, but I believe a dark-adapted eye
in a dark room is an extremely sensitive light detection instrument.

I remember reading somewhere that the sensitivity of the eye to
light is logarithmic, something like 12 orders of magnitude, and
*increases* at lower light levels.

How long would you have to expose that ASA100 film at f1.8 in order
to take an acceptably-exposed picture of, say, a forest in moonlight
which your eye is quite capable of seeing in "real time"?   Tens
of seconds?  Minutes?  What does this say about the effective "speed"
of the dark-adapted eye?

The film test has the advantage of integrating over time all of the
light that leaks into the camera so long as you don't advance the
film.  Its disadvantage is that it costs you part of a roll of film,
the cost of developing, and time before you get results.  Also, if
you change the angle of the camera with respect to the position of
the sun, you won't necessarily know for sure exactly where the light
leak is and at what angle, just that there is one.

        -Greg W.


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