I wonder if you have such a question, why spotting scope can look at the moon, astronomical telescope can not be used for bird watching? And the magnification of astronomical telescope is higher than the spotting scope, so directly use astronomical telescope instead of spotting scope in the end reliable or not?
I can tell you that it is not reliable.
First of all, to clarify the environment of bird watching.
1, working conditions (relative to astronomical telescopes) poor, long-term face a variety of mud, dust, water, etc.
2, need to long-term flat or upward looking
3, with the movement of the bird often focus
So the characteristics of the bird watching mirror are.
1、Birdwatching scopes are sealed dustproof and waterproof
2, the eyepiece has its own 45° elevation angle, and positive
3, there is a focus ring or focus hand wheel, one-handed focus, and the focus stroke is short
The above three points in the astronomical telescope can not do
1, completely unsealed not waterproof
2, fully reversed phase, and difficult to look up.
3, focusing with the focus barrel, is the front and back of the telescope. Focusing stroke is long (because the astronomical telescope needs fine focusing). And then installed so heavy a prism and will change the center of gravity, the tripod is easy to fall down.
There are some other such as astronomical telescopes than birdwatching mirrors much heavier, and the lens coating is very unscratch resistant. There is also a very important point is that: in addition, because birds often move, the need for fast focus and magnification capabilities, birding mirrors can continuously zoom, astronomical telescopes can only keep changing the eyepiece.
In short, what optics scope do what things.