Measuring FS and AFOV of some EPs

[YKSE]

Field stop (FS) is an important measure of an eyepiece, it determines the True Field of View(TFOV) we can see through it, many EPs donot give FS by some reasons, and many have provided Aparant Field of View(AFOV) more in generic terms than actual measurements.

The weather hasn't been great lately, I decided to do some measurement of FS, with method by Andreas , pretty simple setup, and easy calculations, Here's my result:

The first three EP's FS were assumed to be quite accurate, and used here to get the distances, and the averaged distances are used for calculatiing the Field stop bu the measured TROV projections.  As we can see, the numbers are quite close to the known EPs, therefore I'm pretty sure the FS for the MV, Tak orhtho, 50mm Superview etc should be very close.

Another measument done on the Zooms:

Leica's numbers are very close to Andreas measurement in another thread (one single decimal deviation in the 30x setting), despite the measuring scope/condition difference, so I' can be quite confident about my Baader zoom's FSs.

 

David Knisely has describe some methods for measruing AFOV, the flash light method is recommended by many knowledgeable folk too. The setup and measurement are straight forward, here's my result(averaged 6-10 measurements)

Some first impressions:

1. Wider AFOV results in more deviations from simple calculation, especially when there're AMD involved.

2. BCO 18 has AFOV >55°, larger than plossls.

3. Flash light needs to have larger diameter than EP's FS to get proper projected diameter. longer than 20x EP focal length distance is recommended.

So, this are ways to have some scope/EP time when it is

PS. You're welcome to PM me if you need help with the calculations