How good are these monoculars for astronomy?

Question

I bought a 10x40 monocular and a 16x40 monocular from a fellow in ZhengZhou, China. The ad said that all glass-to-air surfaces were fully multicoated. So I figured that I could use them to split some double stars. If the monoculars work well, my eye should be the limiting factor.

The Dawes limit for a 40 mm aperture is 2.9 arcsec.

Assuming that my unassisted eye can resolve a minimum separation of 120 arcsec, magnifications at 10x and 16x should let my eye resolve down to 12 arcsec and 7.5 arcsec, respectively. Either way, the eye's the limit. Ha.

When my monoculars arrive, I'm going to try to resolve Alberio and Theta Serpentis first. Then 8 Lacertae, Zeta Piscium, Kappa Lupi and, down near the limit, Beta Scorpii and Kappa Bootis.

Is anyone familiar with these little instruments? Tried using them?

* Super 16x40 Monocular 40mm Caliber For Hunting/Camping

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220250281938

Answer 1

I have never used them. Should be OK for doubles. The 16 x 40s are going to have a teeny exit pupil, but that's better than one that's too big, I guess. You'll just have to look around until you see the bright spot.

Answer 2

These are designed for terrestial use but they might work on some of the easier doubles if your dark sky conditions are good.   Astronomical lense coatings are different than terrestial lense coatings.  Just beause it says they are coated, you need to ask "coated with what"

You should really get some sort of tripod to help steady the images.  When holding any optical instrument for cellestial viewing, even your pulse can have big effect on the images that you see and your arms can tire easily after a short while.

Answer 3

I am not familiar with them. It will all depend on the optical quality. If the lenses are all ground and polished to the exact right curve, they should work fine. If not the images will not be clear. You can't really tell except by looking at stars with them, and of course you can't do that until you get them and try them. But I am not optimistic that cheap e-bay optics will end up being good. They might, but the chances are not good.

Answer 4

The magnifying power of these instruments make them almost useless for star viewing.