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Posted by Andy Kidd on August 12, 2002 23:09:43 UTC

i assume you me eyepieces [EPs]?

Everybody should have an eyepiece that generates the Mr, or 'magnification of resolution' for their OTA, which will be optimal for general veiwing [using less mag than this will waste resolution, using more will waste light]. Mr with a 70mm aperture will be about 35x- you should get an EP that generates around this mag with your OTA.

You'll also want an eyepiece that generates the M', or lowest usable mag w/ your OTA. I'm not familiar w/ the f-ratio of your scope but if it's medium or long you'll probably not be able to find long enough focal length EP that generates the theoretical M' for your ap size. Best bet would be to go with a good plossl in the 32mm to 40mm range for when you need to maximize your true-field of view.

Though most tout '50x per inch of aperture' as the 'standard' max, or M" [usable max being subjective as well as dependent on seeing conditions]. I prefer a much more conservative [and what i consider to be 'normal'] max of about half the 'rule of thumb', or about double what your Mr is which means if you get a good 2x barlow to use w/ your Mr EP then you'll be about there.

Using the barlow w/ your M' EP should generate an 'intermediate' power and hopefully won't duplicate your Mr so you get the most mags per buck.

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