Is it lowest number when buying good telescope?

Answer 1

If your question is in regards to a telescope's aperature (the front lens in a refractor and the mirror in a reflector), then the higher the number the more detail seen and the higher a magnification the telescope can use.

Answer 2

Optics - microscopes and telescopes all invert the image because if they didnt, it would
mean that another lens had to be added, increasing money cost. A lens is convex on both
sides. That means the middle is thicker than the edges. A microscope or telescope has two
lenses (basically).
The objective lens (usually larger and closer to the specimen or object) which allows the
image of the object to be reduced to a smaller workable image inside the scope.
This image is inverted inside the scope. It is also too small to see with the eye, so you
need another lens, the eyepiece. The eyepiece focus's your eye on the image and magnifies
it so you can see it. Every lens has a focal length, the point at which the image is formed
away from the surface of the lens.

So in which respect do you need to have a lower number? an eyepiece with a low number is greater magnification

Answer 3

Before buying a telescope, I advise going and looking through one. I, personally, was disappointed. After you have looked at the moon once, well, it is boring. Stars even at very high magnification are just points of light. The beautiful cosmic pictures we see on TV or the web are from HUGE telescopes and are the result of long time exposure photographs taken over many hours. The chance of your seeing something really amazing are sorta small. So, before laying down a lot of bread, take a look through one. See if it is worth while.

Answer 4

If your question refers to the f/stop number (as opposed to the aperature) then the question should be explained further. For visual use it doesn't matter as much, but for photography it does. The f/stop is the ratio between the diameter of the objective lens or mirror and it's focal length.

My telescope has a 2000 mm focal length and a 200 mm mirror. So it's f/stop number is f/10. It is ok for photography and visual. I believe the smaller f/stops are better for photography, but that could be backwards. Ask your dealer, or try searching the web for which is better.