Someone on DPReview has asked me to post a table of lens formulas in object space and image space that I posted there a couple of years back. DPR has almost shut down, so I am posting it here instead:
April 9, 2023
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You can play with these visually at the PhotonsToPhotos Thick Lens Optical Bench
For example -
I find this formula very useful:
D = f ( 2 + m + 1/m) + h
f and m with the previous meaning
D distance between object focal plane and sensor
h = thick lens parameter, signed separation of principal planesD and m can be easily measured with a setup as below. For some old lenses f and h are well documented. For modern zoom and/or internal focus lenses, we have two unknown values, f and h, which are both functions of the m setting in general. For fixed zoom and m ( m by distance ) settings the two unknown values can be determined by doing 2 measurements with different extensions by inserting an extension ring or a bellows.
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Yes. I prefer extension tubes because the extension is more exact.
Using 3 extension tubes in combination get me 7 measurements which is more accurate than 2.
There are several results of using this technique at PhotonsToPhotos.
For example Focal Length at Closest Focus - 105mm f2.8G IF-ED AF-S VR Micro-Nikkor
