Re: do lens changes fog IR?

["Peter Badcock"<pbadcock@xxxxxxxxxxxxxxx>]

______________________________ Reply Separator _________________________________
Subject: do lens changes fog IR? 
Author:  <infrared@xxxxx> at Internet
Date:    27/4/99 2:14


I hope this is the right procedure to post a question...  Has anyone else had 
problems with fogging IR film when changing lenses?  I was shooting at Joshua 
Tree when a couple coyotes approached and I wanted a longer lens.  I changed 
my lens without using a changing bag.  All my coyote pictures are flat and 
have uneven exposure.  I can't quite tell if it's fog or not.  However, all 
the other pictures on the roll have perfect exposure.  My friend says it's 
because coyotes are tricksters.  I am looking for a more scientific 
explanation.  The camera is an old Canon AT-1.  Thanks, Gregg


Hi Gregg,
         I can't see any reason why changing a lens over would cause the shutter
to open up and expose a frame.  When the lens is on the camera and the lens cap 
off the things that limit/reduce the light getting to the film are 

i) the shutter
ii) the mirror (in an SLR) which usually lifts up out of the way during a shot
iii) the apperture  to a small extent of course!.

all of these limit the amount of light in varying degeres, the ultimate point of
non transmission is at the shutter plane.
regards
Peter



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