Re: Finding camera leaks

[P3D Greg Erker <erker@xxxxxxxxxxxxxx>]

Greg W. writes:

>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?

  For a medium or bad leak I can believe the eye is more sensitive.
For a small leak that only shows up after you have been out in the
sun for hours I believe the film is more sensitive (since it
integrates for that whole time) than your dark adjusted eyes.

  I don't have quantitative numbers but if you do a long exposure
of the night time sky using fast film (that doesn't suffer too
much from reciprocity failures) you will see more stars on the
resulting photo that you could with your dark adapted eye.

  I don't know at what level of "dimness" the film becomes more
sensitive though.

>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.

  Agreed.

>  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.

  Unless you have a very bad leak the light will only fog a small
region around where it entered. So I think you will know where the
leak is (though not necessarily the angle at which it leaks).

  In summary, try the bulb test, but if you still get small leaks
when outdoors for a long time, try the fast film method.

My opinions - Greg E.



------------------------------