Quote:
Originally Posted by PeterEde
I've read that anything beyond 120X is over doing the ED80?
I guess that's up to the individual to determine.
Thanks for the input Astro
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Your exit pupil at 120x with 80mm telescope is 80/120 = 0.667mm (Or to get 120x you need 5mm eyepiece; exit pupil = 5/7.5 = 0.667 (7.5=f/ratio)).
The image starts getting a bit dim below 0.5mm exit pupil and/or floaters in your eye become visible. Some people have no problem with 0.35-0.4mm exit pupil. With an 80mm/f7.5 telescope you get the following:
6mm eyepiece = 0.80mm exit pupil and 100x mag.
5mm eyepiece = 0.67mm exit pupil and 120x mag.
4mm eyepiece = 0.53mm exit pupil and 150x mag.
3mm eyepiece = 0.40mm exit pupil and 200x mag.
Given you have a refractor with unobstructed view, 200x with a 3mm eyepiece would be achievable readily albeit the image may be a little on the dim side but it does depend on the object as to whether that is a problem or not.
An alternative to the zoom would be say a 5mm T6 Nagler giving you 120x and 0.67 deg. true field. This will give you the full lunar disk with a nice amount of room to spare at 120x. Wow! The Type 6 Naglers do come up used on this site often at good prices.
I find 120x only just enough for planets like Jupiter & Saturn and often crave for more power although the image at 120x always looks sharper and that depends a lot on seeing.
Just some suggestions and yes expensive but with eyepieces, if you buy quality, you can use them on any telescope and they will always perform well.
Whatever you choose, enjoy!