Horizon 202, some IR fogging problems solved.

["Keith Davison" <keith.davison@xxxxxxxxx>]

A while ago I posted describing a fogging problem that I had using my 
Horizon 202 with HIE (87C filter), I was getting a a line of fog along the 
sprocket area on the bottom edge of  the film (top in the camera).  This 
fogging was densest at frame one and gradually decreased, 
disappearing at frame six (Horizon frames).  An identical pattern 
appeared on every roll of HIE I used, but was not present on standard 
colour or b&w film.  I suspected that the fogging was due to IR light 
leaking down the take up spool shaft (the top has no flange).  The first 
frames would be fogged, but as the diameter of the spooled film 
increased, it would be taken out of the light leakage area.

I used black electricians tape (guess I must have been lucky with the 
brand!), and covered the hole above the take up spool, putting tape right 
up to the spindle that the spool runs on.  The edge fogging problem has 
completely disappeared.

Another fogging problem with my 202 was that when one frame was 
grossly overexposed a series of bands appeared on preceding frames. 
The bands extended across the whole film width, right into the sprocket 
areas and were darkest on the frame immediately preceding, gradually 
decreasing in subsequent frames.
This is caused by reflection of the increased stray light off the chrome 
plated transport sprocket, with the lack of an anti-halation layer the light 
penetrates the exposed film wound on the takeup spool producing the 
bands.

Apart from not overexposing, the cure for this is to paint the chrome 
sprocket with matt blackboard paint.

Now, if I can just solve my other banding problems.............

Keith Davison
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