Ah, those numbers were filled in by the excel calculations (I thought they were fixed): I was trying to find a good wide field EP for my Stellarvue 9X50 finder scope which has a FL of 200 but that generated some absurd Exit Ps! I still get a lot of EPs with exit pupuls over 10mm based on my 1000mm F/5.3 scope.
The EP that came with it is 23 mm (~50 AFOV?) and all the stars on towards the edges are comma shaped. Obviously, it has to be 1.25 inch, I don't want to break the bank on this and was looking at the Explore Scientific 68° 24mm - with a calculated exit pupil of 6 mm. Maybe a bit too high for my eyes now.
I hope this isn't too naive, a bit new at this!
At f/5.3, it's fairly safe for individuals of any age to use a 5mm exit pupil, or a 26-27mm eyepiece.
If your pupil is larger, you won't lose any light, but the image could be a bit brighter at lower power and larger exit pupil.
If your pupil is smaller, you lose a bit of light, but since the magnification is low, the image will be bright anyway.
Regardless of what exit pupil results, I see little reason for scopes to go below:
30x on a 4"
40x on a 6"
50x on an 8"
60x on a 10"
70x on a 12.5"
90x on a 16"
100x on a 20"
Yes, going lower means a brighter image, and a smaller image scale, and that could be useful for an object here and there.
But matching magnification to aperture means that, as I see it, there is little value in magnifications below about 5-6x/inch of aperture.
I'm certain some will disagree, but though the images at lower powers are bright, the magnifications are too low to see the objects with a decent scale.
On the other end, those of us above a certain age tend to have a lot of floaters in the eye that can interfere with the image when the image is bright, like the moon or planets.
It's usually quite safe to use 1mm as your smallest exit pupil for eyepieces, which means magnification = diameter of the telescope in mm.
Higher powers can be useful for double stars or the Moon at times, but it's cost effective to create such powers with a Barlow because those magnifications won't be used as often.
A 1000mm focal length f/5.3 implies a 190mm scope, or about 7.4". A 27mm eyepiece yields 37x. You might find that a bit low in magnification as a low power.
I think you'd be happier with 40-50x as alow power (25 to 20mm range)
P.S., your finder has significant aberrations because it is very short in f/ratio--f/4, which is incredibly fast for a lens. The eyepieces that work well in that finder will not be inexpensive, alas.
I think the eyepiece in question might be a Kellner, so the ES you contemplate for the finder might be a step forward. But that assumes the lens is good, which is a big IF.
Edited by Starman1, 10 April 2020 - 06:09 PM.