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True field of view
As I understand it - regardless of whatever size eyepiece you use, the theoretical TFOV as claculated from eyepiece size, focal length of the telescope, and AFOV is still restricted by the field stop diameter.
So say my 4.5" f8 newt (1.25" holder) with a say 40mm plossel eyepiece gives
mag = 900/40 = X 22.5, (and an exit pupil (e=a/mag) of 114/22.5 = 5.07mm)
TFOV (calculated) = AFOV/mag = 50/22.5 = 2.22 degrees
TFOV (field stop) = field stop/focal length X 57(degrees), and the field stop max in a 1.25" eyepiece is 27mm (actual)
So its actual TFOV is 27/900X57 = 1.71 degress (102 minutes of arc).
It does not matter whether it was a super plossel or Nagler in this respect as the field stop limit greatly curtails the TFOV.
A 31mm plossel would give a calculated TFOV of 50/(900/31) = 1.71 deg.
Thus the 40mm and 31 mm give the same TFOV in my scope, but the 40mm has X 22.5 mag versus X 29 mag, and exit pupils of 5.07mm versus 3.93mm.
It also follows that a 25mm Super wide plossel (70 degree AFOV) has a calculated AFOV of 70/36 = 1.94 degrees - and would be utterly wasted.
There is no point for me buying Super wide angle eyepieces (approx 70 AFOV) in the F8 more than about 22mm if what I want is larger fields of view. I may as well get a good plossel. If I do anyway, I will see the same field ov view, merely at greater magnification (If that is what I want).
Did I get that right?
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