"As you're focusing closer than infinity the sensor has to be moved further back to compensate which leads to the 192mm FL."
That's not how we usually do it. The tube lens stays focused at infinity. The objective is optimized for a fixed working distance, and we usually move the whole assembly (camera + tube lens + objective) to focus.
Astrophotographer contemplates extreme macro
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rjlittlefield
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"Exit pupil" is just the apparent position of the aperture, as seen from the sensor side of the lens. It is relevant when calculating pupil factor or angles of light as they strike the sensor.
The phrase "exit pupil" is often used in error, when the writer actually means the "rear principal point". A simple distinction is that focus is measured from the principal point and is not affected by where the lens designer placed the aperture along the optical axis. If you're talking about focus, exit pupil is not relevant. The rear principal point is located exactly one focal length in front of the sensor, when the lens is focused at infinity.
I believe that nathanm's measurement of 170 mm for the DCR-5320 AB was determined for the distance that gave best corner quality. "We started with tube lens focused at infinity, but sometimes the best result was slightly off of that." This is not the absolute best position of the rear lens for minimizing spherical aberration in the center of the field. (That would be with the rear lens at infinity focus.) But it is close enough to not degrade the center, while apparently improving the corners.
--Rik
Edit: to correct the number -- thanks, Lou.
The phrase "exit pupil" is often used in error, when the writer actually means the "rear principal point". A simple distinction is that focus is measured from the principal point and is not affected by where the lens designer placed the aperture along the optical axis. If you're talking about focus, exit pupil is not relevant. The rear principal point is located exactly one focal length in front of the sensor, when the lens is focused at infinity.
I believe that nathanm's measurement of 170 mm for the DCR-5320 AB was determined for the distance that gave best corner quality. "We started with tube lens focused at infinity, but sometimes the best result was slightly off of that." This is not the absolute best position of the rear lens for minimizing spherical aberration in the center of the field. (That would be with the rear lens at infinity focus.) But it is close enough to not degrade the center, while apparently improving the corners.
--Rik
Edit: to correct the number -- thanks, Lou.