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Old Thursday 14th December 2006, 23:50   #15
henry link
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Join Date: Feb 2004
Location: north carolina
Posts: 4,117
Originally Posted by greg g
.... On a previous thread I seem to recall it was mentioned that the power of an eyepiece (92x) should not exceed the size of the scope (80x), your Astro-Physics is a 92x. I don't know if this is true, what do you think of that?
If that is true should I then consider a 6mm Burgess Optical/TMB Planetary for a 80x scope? Is that what you meant about "if it will reach focus"?
The famous telescope maker Jean Texereau says that the "best" magnification for detecting small low contrast planetary details (comparable to small low contrast plumage details on a distant bird?) is 20% above a telescope's aperture in millimeters. More magnification causes too much loss of contrast and less magnification doesn't make the details large enough. For an 80mm telescope that would be 96X, but the scope has to be really good for that to be true. Many if not most birding scopes probably do run out of detail and contrast at a lower figure. Maybe you could order or borrow both focal lengths and return the one that you don't like.

I agree with Lou that you should avoid eyepieces with short ER and narrow fields, but the BO/TMB Planetaries are actually pretty good in those categories. The 5mm has 16mm ER and a very well corrected 60 degree field. I think they'd be taken more seriously if the price were raised to $300

If an eyepiece can't reach focus in a particular scope that means it will only focus at close distances. The focuser doesn't have enough travel to bring it to focus at long distances. You'll probably find that not all 1.25" eyepieces will be focusable in your Swaro.

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