TheSkySearchers

A really great article.

https://skyandtelescope.org/astronomy-e ... inoculars/

Thanks very much. Good article.

Hello Refractordude. This is an excellent article and explains a lot of good rules for selecting and using binoculars. I have always followed the 6mm or less exit pupil rule. And, as your eyes get older, the dilation of the pupils becomes less. For example, my old Focal (Kamakura Optics) 7x35mm binoculars result in an exit pupil of 5mm. My much newer Celestron 15x70mm binoculars result in an exit pupil of 4.66mm. And, this is important even after your eyes have become dark night adapted with the rhodopsin having been released.
https://en.wikipedia.org/wiki/Rhodopsin
Thanks for this informative link Refractordude, and the best of regards.

Thanks for posting that one.
I haven't seen that article before.

Lately of been using my binos more and more.

Great article. Thank you for posting.

Very nice article - and useful, thanks for posting.

I kinda wonder about his quick rating system: 10x50s = 500, 20x60s = 1200, 15x70s = 1050. The 60s are rated highest, but they only have a 3mm exit pupil. Seems to me 3mm is pushing things or am I missing something here?

I just returned a pair of 10x50 binoculars. The 7x50 works best for me. The clarity is just best for my physiology. I may get a pair of the APM 7x50 ED before Spring. The Levenhuks that I have are really good, but I want something wider than 5.7 degrees. I was just out back looking at the Moon with passing clouds. Everyone should own a pair of low mag wide field binoculars. The Levenuks can bring Aldebaran, Ain, and Prima Hyadum into view with surrounding stars. Dual refractors/binoculars rock. Left click the image.

very good article , thx

pakarinen wrote: ↑Mon Nov 16, 2020 5:02 pm I kinda wonder about his quick rating system: 10x50s = 500, 20x60s = 1200, 15x70s = 1050. The 60s are rated highest, but they only have a 3mm exit pupil. Seems to me 3mm is pushing things or am I missing something here?

It depends. A 3mm exit pupil isn't bad for looking at large faint fuzzies. If you're in an are of light pollution it might work better than a 5mm exit pupil.

I ran into the Bishop visibility factor several years ago in the May copy 1995 of Sky & Telescope. An article by A. MacRoberts.
Holger Merlitz referred in his book "Handferngläser", 2019 Verlag Europa-Lehrmittel, to three other publicists about the matter. ( How good is your reading technical German language? It'd better be excellent)
It comes down that the four calculation methods do not differ all that much in their outcome. Bishop's method is by far the easiest to remember.
All methods are based on magnitude 6 or better naked eye limit.

In my experience and apparently of notFritzArgelander too, much depends on the light pollution.

A 3mm exit pupil isn't bad for looking at large faint fuzzies. If you're in an are of light pollution it might work better than a 5mm exit pupil.

For instance: M42 in a 20X60 is even a bit more impressive than in a 20X80 under light polluted skies. ( exitpupil 3 mm versus exitpupil 4 mm) Darker background, so more contrast with its background. Under really dark skies, the 20X80 might be more impressive.

The high numbers of the Bisshop calculation might lead to false expectations though. 500 against 1600 for instance for a 10X50 against a 20X80. It seems a giant leap but in reality it is only a difference of 1.3 magnitudes. Visible of course, but not as spectacular as it seems when you hear 500 versus 1600. Knowing this, a difference of 250 on the Bishop scale might not be that impressive as one might expect.

My home night sky is so light polluted I do not bother with DSO. Andromeda looks like the size of slightly transparent Brazil nut, and that is with a 6" aperture refractor. At Maryland's Point Lookout State Park, brighter galaxies are no problem with 7x50 binoculars. Left click the image.