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Re: HELP!!! I Need A New Secondary Mirror. What Size?

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Posted by Robert May on May 10, 1999 19:05:39 UTC

No, I'm not. What I'm saying is that the mirror size is not that important (.077" difference in dia.) unless the mounting method would cause you to have a problem. The size as far as optical needs are concerned is all over the place. In the newsgroups major arguments have erupted on this subject because one person wants his scope to be for planetary work and will accept the loss of light at the edge of his EPs and another wants to use low power EPs for nebulas and other extended objects or for photography and doesn't accept the loss of light at the extreme edges of the FOV. There is a program that will tell you what happens when you set the size of the secondary to a particular size on the web. BTW, there is an immense amount of free software on the web that does all kinds of things for the telescope maker and the sky observer. If you go out and find the software and play with it you will understand how secondary size affects you scope and maybe you will decide to change the size of yours. As far as coating firms, there are several listed in the back of both the Astronomy magazine and Sky and Telescope magazine and if while you're looking around you find a recommendation for a coater over there in Europe then use them. The costs shoud be lower than getting a new mirror.

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