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72.0° |
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69.3° |
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66.4° |
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63.7° |
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These preliminary results indicate that there is a simple relation (see bellow) - perhaps even linear between the maximum aperture number and the Theta 3. It should however really be monotonic, see page on LENS SPEED INDEXING POST gearing.
The lens repair manuals say to use a custom gauge to control the MAIP angle (also known as "theta3") and the allowance for the MAIP position is only +- 8' (degree minutes).
I measured the angles on print-outs of lens scans but there seems to be too many sources for error in the lens - scan - print - measurement route.
An option could be to measure on a "live" true AI lens with a corresponding maximum aperture for any given modification - or to transfer the position onto a female f-mount ring, see bellow.
This method was successfully used to transfer the LSIP position to an AI modified lens.