Re: Have refractors hurt the hobby?

From: Jon Isaacs (jonisaacs_at_aol.com)
Date: 11/06/04 

Date: 06 Nov 2004 11:00:14 GMT

> But because of this, and the fact that I got mine
>at London Drugs and not Vancouver Telescope, I'm lucky because I'm not
>getting the horrible chromatic aberration that I would get from a
>cheap refractor.

The "typical cheap refractor" is a 60mm F11.7 achromat and does not have
"horrible chromatic aberration."

One rule of thumb for acceptable color in a achromat is that the focal ratio be
5 times the objective diameter in inches. (Another less conservative rule is
3X.) 60mm=2.36 inches x 5= 11.8

This means that the scopes are nearly color free. Most often the objectives
are pretty good. Its the rest of the scope that is lacking.

jon

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