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Anonymous
>>265391 how did I know someone was going to say something idiotic like that? A mirror telephoto does not take the place of a refractive telephoto. It's for use with objects/subjects that are far away and when it's focused faraway (a say a bird, the moon, a moose on the other side of the valley), you compose so that there ain't any foreground that is out of focus. The HF distance on a 500mm f/8 used with say a D300 is about a mile. Focused at 1 mile, everything from about 1/2 a mile to infinity is in focus. Does it perform as nicely as a refractive 500? Of course not but it's 1) much cheaper (a nikon 500mm mirror lens can be found for about $300, a 500mm f/4 is over $7000) 2) much lighter 3) much less expensive 4)a lens that is going to be used only the minority of times
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