I am currently working on calibrating a number of lenses for the new Mercury camera, to assist with the creator and future possible users of this camera.
This is being done by eye - focusing on targets at certain distances, using a digital camera for critical focus. However, some ultrawide lenses do not really work this way due to short FFD. Ground glass focusing is pretty hard to be exact. And finally, human error can be a serious problem!
I was thinking today that it seems like there should be a formula for this. Knowing of course the focal length as well as the FFD, the amount of extension needed for each distance should be calculable right? And then by measuring the helical extension with a caliper and dividing that out by 360 degrees, a reasonably accurate focus scale could be made.
Am I correct in this? If so, what is the formula(s)? I imagine an Excel spreadsheet with the data and formulas could spit out numbers pretty quick, and then I could double-check them on the camera to be sure.
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