(Thanks to Ed Ting for permission to serialize his article here. I think it’s mandatory reading for anyone who is considering telescope binoculars for astronomy viewing. Ted)
Testing Under the Stars
If and when you do get a chance to test binoculars under the stars, take it. A star at night is the most stringent indicator of optical quality. You may even find a daytime “artificial star” such as sunlight glinting off a distant insulator on a power pole or a distant piece of shiny metal.
Center it in the field of view. Looking with one eye at a time, can you bring it to a perfect point focus? Or, as you turn the knob, do tiny rays start growing in one direction before they have shrunk all the way in the direction at right angles? This astigmatism is especially bothersome when viewing stars. If you have astigmatism in your eyes, be sure to wear your glasses when doing this test.
If, as you turn the focus, little rays start growing out of the star in all directions before the rest of the star comes down to focus, you’re looking at spherical aberration. This problem too may be in your own eye, even if you’re wearing your glasses. If it is, all binoculars with a given size exit pupil will show the same problem. To reduce it, choose higher-power binoculars; these yield a smaller exit pupil for a given aperture. Unfortunately, your eye’s spherical aberration cannot be corrected with glasses.
Now move the star from the center of the field to the edge. It will go out of focus unless you have a perfectly flat field and freedom from various other aberrations. As a rule of thumb, no degradation should be visible until the star is at least halfway to the edge of the field.
All our Barska telescope binoculars and astronomy binoculars have limited lifetime warranties from defects.
Tags: astronomy, astronomy binoculars, Barska, binocular astronomy, telescope binoculars
im normally wandering across the online world virtually all of the night which means I have a tendency to browse a good deal, which is not generally a beneficial matter as most of the pages I find are constructed of pointless rubbish copied from different internet sites a zillion times, nevertheless I have to compliment you because this site is in fact quite informative and offers some unique substance, therefore many thanks for breaking the trends of simply copying other individual’s websites, if you ever wanna take up a couple of hands of myspace poker together just shout out – you have my e mail