Shopping for astronomy binoculars?

Question

I was wanting some binoculars to use along with my telescope, but I have no ideas what the numbers mean. How do I know if what I'm looking at buying is a good quality of binoculars for viewing the night sky. I have a meade etx 60 telescope, that I bought around January, and the only reason I bought that was cause it was on clearance from $200 to $50. I recently got addicted to sight seeing at night skies, but now I want to buy binoculars and want to know what the numbers mean, and how to determine what is better ? Example, ( 25-125x80) or (20X60). These are just examples, and if anybody knows of a great place to buy binoculars for a reasonable price that would be great also, thanks.

Answer 1

The first number is the magnification, the second number is aperture (size of the objective lenses in mm). A binocular that lists two mag numbers, like 25-125, is probably a zoom binocular; these are best avoided, their quality is generally not good, and you are paying for the whiz bang zoom feature that is pretty useless, really.

The 20x60 sounds like a pretty big binocular, with a magnification that is pretty high. I suspect that this would be difficult to hold steady, and would show such a small piece of sky that it would not complement your telescope, but rather compete with it - and probably lose.

Most astronomical binoculars are either 7 x 50 or 10 x 50 models that are either multicoated or fully multicoated. Multicoated means at least one coating - MgF has been applied to each of the optical surfaces, and the outside of the objective lens has multiple coatings. Fully multicoated means that all of the surfaces have mutiple coatings.

20 x 60 may work, but you might want to try the other ones first. Big binoculars like these occasionally show significant chromatic aberration when viewing small, bright objects, and you may need a tripod to use them at all. This is easy to check out at a local astronomy club open observing session. Good Luck and Clear Skies!  

Answer 2

Don't get anything smaller than 10x50 and they need to be aligned properly if you want to use them for Astronomy.  Look through them at a far away distance (moon is best) and look with both eyes open,  You should only see one image.  If you see 2 or more, then they are not properly aligned and will not work for astronomy.  you also need a tripod for them because you will be too shaky holding them.  Even your pulse will make them shake.  Terrestial viewing is much different than astronomical viewing when it comes to binoculars.

Answer 3

You don't want to hand hold anything above about 10X.

The field will be too small, and the image too 'shakey' for comfort.

25-125X x 80 means 25 to 125 Dia.s magnification from an 80mm lens.

(You will get lousy light gathering at anything but the lowest magnification, they'll be useless without a good tripod.)

The 20X 60 you mention might be used in daylight, but you wouldn't be happy with them at night.

A simple rule for binoculars:

Divide the objective lens by the magnification to get the 'exit pupil`.

You want about 4-5mm minimum for night viewing to match the size of your eye's dilated pupil, so something like 10x 50 is reasonable.

Don't get cheap glasses, they're a waste.

The cheaper 'zoom' models are total trash.

If you're on a budget, a good set of 7 x 35s will beat the heck out of

a cheap set of 10 x 50s.

I got a nice pair of 10 x 50' s by Steiner on special from

sportsmans guide at $300.

(Good glass is expensive.)

Answer 4

The numbers relate to the focal distance over the aperture.

for astronomical and hand-held use a lower power (less than 10)

with a wide field of view would be recommended.

Answer 5

The first number is magnification and the second number is diameter of the objective lenses in millimeters. The usual recommendation for astronomy used to be 7X50. These days they seem to favor 10X50. That is 10 power with 50mm lenses. I have a set of 10X50 that I got just for astronomy, and my son has a set of cheap 7X35 he got at Academy Sports (see the source). A while back when there was a comet in the sky I looked at it through both sets of binoculars, and the cheap 7X35 binoculars showed it MUCH better! I was very surprised!

Answer 6

I've had 7x50s for my whole life, and they're ideal. 7x magnification gives a wide and bright field of view with a 50mm objective; greater magnification will decrease the field of view as well as brightness, plus increase any errors in the optics.

7x50 is ideal because it produces an 'exit pupil' of 7mm (50/7) which matches a human eye when it's dark-adapted. Smaller objective lenses show less detail and brightness, and larger ones make the binoculars too heavy (and wobbly) to be practical. Any binocular magnification greater than 10x is really a waste of money.