There are a wide variety of double mirrors on the market. The price difference is more than 10 times times, the lack of experience inevitably cross-stitch eye. In fact, for astronomical observation, the principle of purchase is relatively simple: in the price range you can afford, as far as possible to buy large caliber.
Layman customers often think that the higher the magnification, the better, some manufacturers also deliberately use false high rate to lure buyers. However, the ratio of double mirrors is limited by caliber. High-magnification binoculars may be very convenient for the observation of a few celestial bodies, such as Ganymede and binaries, but the higher the magnification, the narrower the field of view, making it difficult for you to find objects in the stars. Especially in the bright star sparse days to look for dark targets, high-power binoculars obviously less than the macro-mirror. If the binoculars do not have a bracket for holding the observation, you will feel the target wobble in the field. The higher the ratio, the more serious the handheld observation of binoculars should not exceed 8x.
During the daytime watching the game, 7x35 's binoculars are almost as good as 7x50 's, but the stars are very different at night. The larger the telescope, the darker the visible stars. Many celestial bodies are difficult to see, not because they are too small, but because they are too dark. 7x50 two-cylinder mirror than 7x35 of the set light strength of about 1 time times, at least to see a star. With the author's experience, 7x50 binoculars are suitable for astronomy enthusiasts, and its price is moderate. Can be used for many observational projects. The caliber is larger, the price rises straight, and the special bracket is not available. 35 mm caliber should be the lower limit of astronomical observation binoculars, buy a smaller-aperture double mirror, as the same funds to buy 50-60 mm achromatic objective, homemade a single tube of the telescope, the use of better results.
In addition, the army, navigation, geological and mineral departments sometimes have the old double mirror discount treatment, they are slightly renovated can be used for viewing stars. But there is a military antiaircraft gun command binoculars, caliber 80-100 mm, equipped with flexible operation of the flat-type bracket, but not suitable for viewing stars. Because their field of view is very wide (can hold the entire Orion), the magnification is too low, the general comet, the cluster, the nebula become and the star is also a small point, and the coma image is bad.