I just ran the classic ISO speed test for 4x5 TMax100. I got an ISO of 64. Now, I shoot Tmax100 in 120 as well. Do I need to re-do the test for 120 Tmax100? I'm gonna be using the same RS developer for the 120. I though 4x5 sheet film is thicker than roll films. Does this make a difference? Thanks
You should rerun your test with the 120 film just to be safe.
It probably will come out the same, but different film bases will give you different readings.
Different lenses. Different shutters. Maybe different meters.
Brian
I'm not sure how you meter, test your film or anything else. However, while my own testing indicated that Tmax 100 behaves in a similar fashion in Tmax RS in both sheet and roll film formats, you may find that the limitations of having to subject an entire roll of film to the same development may change the way you shoot and develop roll film compared to what you do with the same film in sheet formats. I had very similar results with rotary processing Tmax100 in formats from 35mm to 4X5, but I tend to shoot with slightly different speeds - I shoot roll film formats at 50 or slower and process identically to N dev on my sheet film which is shot at 64. This has quite a bit to do with the characterictics of Tmax 100 - a very ugly stubby toe and a LONG curve... - basically, when in doubt with this film, overexpose a little rather than risk blocked shadows.
Your lenses and shutters will make enough of a difference that separate tests should be done. It doesn't take long so do them and get good results.
Equipment calibration is the key. If meters, shutters, and apertures are the same, it will come out the same.
I might add different lenses will show shadow detail differently. If you are using older LF glass, shadow detail may be lighter. If you have modern LF glass and good 35mm, results are the same.
Read Lee Frost's book on black and white and forget all this testing BS.
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