I have recently obtained a Phochron XA digital shutter speed tester and have made a little jig to mount my dozen or so lenses (all on Technika-style boards) so I can quickly test them through the various shutter speed settings. Luckily, only one of my lenses/shutters is off, and a bit too inconsistent, on certain speeds such that I will need to send it out for CLA or repair. All the other lenses seem to be quite consistent from one click to the next, and fairly close to the various speeds indicated on the shutter dials -- BUT OF COURSE THERE ARE SOME VARIANCES!
My test data are speeds expressed as fractions like 1/28.4 seconds (where the target was 1/30), and these data can be easily converted to milliseconds. My question is how do I determine the aperture exposure corrections to apply when taking photos with these lenses, in order to correct for the results of my shutter speed tests (whether the lens in question was found to be a bit fast, or slow)? My Compur or Copal lenses shutters allow me to add or subtract exposure in 1/3 stop increments, but how do I relate those increments to the shutter speed test data (which are on an arithmetic scale)?
Finally, if someone might have, and be willing to share, an Excel spreadsheet set-up for this purpose, it would be greatly appreciated.
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