Struan, we're all working in a vacuum.
Yes, Dan, and this situation greatly simplifies our calculations wih pencil and paper, since the refractive index between glasses is exactly 1.0000000 and not 1.000293 in air.
---------------------------
And going back to purely academic exercises, as usual, it is shortly after posting my long message that I remembered from the series of lectures I attended a long time ago, that determining the pupils of a system made of 2 thin groups is best achieved by considering the intermediate optical space between the two thin groups. Simply because the apertures limiting the sizes of the 2 groups are self-imaged in this intermediate space.
Hence the quickest procedure to find the pupils for the Galilean telescope, (e.g. (4 / 3 / -1) for a 4x instrument) the classical refractor telescope (2 positive groups e.g. a 8x pair of binoculars (8 / 9 / 1) ), the Peztval lens represented by 2 equivalent singlets in terms of focal lengths and pupils (and of course NOT in terms of aberrations!), and the academic telephoto analysed above, is to consider the angular diameter of both groups as seen from a point in the intermediate optical space view which is simply the focal point F'1 of group#1.
In the case of the academic telephoto (1.5 / 1 / -1), it is easy to see without any calculation that the smallest aperture seen from F'1 is the entrance aperture as long as the 2nd aperture is bigger in diameter than one-third of the 1st aperture.
And this approach proves for the same (1.5 / 1 / -1) design that any section of a cylindrical barrel connecting two singlets of the same diameter will not act as the pupil.
At least in infinity-focus setting.
See the attached sketch.
Reply With Quote
Bookmarks