http://www.astropix.com/HTML/I_ASTROP/LENSES.HTM
High-End Lenses vs Telescopes
Both Canon and Nikon make fast high-end lenses in the 300mm to 600mm range with apertures from f/2.8 to f/4. These lenses are very expensive, costing thousands of dollars. At this price point you are into the same price range a expensive high-end apochromatic refractors. This naturally raises the question of which work better for astrophotography.
If you need an optical system for both daytime photography and astrophotography, these high-end lenses can work. If you need a long focal length with a very fast aperture, say for nature or sports photography, you won't really be able to use a telescope at all. You can, however, use a 400mm f/2.8 lens to shoot the stars, if you have a sturdy mount capable of handling the weight and if you don't mind compromising a bit on optical performance when the lens is used wide open.
The optical performance of these lenses on starfields are usually pretty good when used wide open. Their performance, like most other lenses, will improve when they are stopped down. But if you are going to spend $6,800 on a giant piece of glass like this only to stop it down, then you are definitely better off going with an apochromatic refractor with a telecompressor/field flattner. These scopes are made to do one thing - image stars at infinity. They also make excellent instruments for visual observing. If you put a high-power eyepiece on an expensive super telephoto, you will be very disappointed in it's visual performance.
So, if you need dual use for daytime and astrophotography, get a long telephoto. If you need dual use for astrophotography and visual astronomy, get an apochromatic refractor. |
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上架关防抖是常识。。。。。。。。。。你用过最好的脚架是啥？用过捷信么..?曼富图也行？