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Old 1st September 2010, 08:35 PM
Joe Bowes Joe Bowes is offline
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Hi Les, can you help? I've just developed my first roll of Rollei 120 IR400 and, well, there's nothing there, not even a faint image of anything (clear rather than black).
The test frame with no filter and taken at ISO 400 is perfect, in fact I'd say on first look it has the edge over my TRI-X.
I shot with a Lee Filters 87 IR filter and ISO 12 bracketed to ISO 6. Due to the brightness this equated to shutter speeds of between 1/8s and 2s over 11 frames and 2 locations.
What did I miss?
Cheers
Joe
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Old 1st September 2010, 10:32 PM
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Les McLean Les McLean is offline
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Hi Joe, you say that due to the brightness the exposures were between 1/8s and 2secs. Do I take it that the light on the subject was was low or very bright? If your first exposure without a filter produced a good negative the only cause of the remainder of the film being blank is lack of exposure. The exposure range you describe is only 4 stops which is negligable when you have to take into account the density of the filter and the fact that you used ISO6 and ISO12. That is a very slow ISO rating which will require a lot of exposure. You also didn't tell me the lens apperture which would also have a bearing on exposure time.

IR filters are extremely dense so I'd suggest that you load another roll, select a subject, make a meter reading through the filter, expose the first frame at that exposure and then without moving the camera (I hope you are using a tripod) expose the remainder of the roll increasing each exposure by one stop more than the previous. Make sure that you keep a record of the frame number and the exposure so that when you develop the film you can decide which is the best one and trace the exposure through your notes.

I'm fairly certain that you will find that each exposure will offer something different in effects and that all will produce slightly different prints although they are likely to require a lot of exposure at the printing stage because of the probable density of the negatives. IR film is interesting when you start playing around with exposure.
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Old 2nd September 2010, 02:55 PM
Joe Bowes Joe Bowes is offline
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Thanks Les, I read somewhere that rating the film at ISO 12 for exposure calculations would be a good starting point ie + 5stops? - oh dear!
I didn't try to meter through the filter as I can't see anything through it, so I didn't think the meter would work.
I metered at F16 1/250 and 1/500 without the filter (subject & sky) and shot at 1/8 = 5 stops? I also tried F22 @ 1/2,1 & 2s (Hassy 501CM).
Lee say the filter starts to allow light through at 730nm if that helps - which begs the question why it has a number of 87?.
If the meter doesn't work through the filter I guess I should start my exposures at 4s (as I know 2s doesn't work) and, like you say, move up a stop on each frame and see where I get to - does this film suffer from reciprocity failure as well?
Thanks for your help
Joe
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Old 2nd September 2010, 04:26 PM
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Les McLean Les McLean is offline
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To my knowledge all film will be affected by reciprocity failure but if you do the test I suggest you will find the point at which the film starts to record information. I wouldn't bother with calculating reciprocity at this point.
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Old 2nd September 2010, 04:37 PM
Joe Bowes Joe Bowes is offline
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You're right of course.
Cheers Les
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