Tuesday, February 16, 2016

how low can you go?

Researched long length eyepieces for Tony...

Found a handy calculation for determining the lowest power eyepiece. For the lowest power or longest focal length eyepiece, you use the factor of 7. I.e. multiply the f/ ratio of the 'scope by 7. The C14 is f/11 so that means 77mm.

Tele Vue stops at 55mm.

Found Russell Optics and their special 2-inch ocular offerings including 65mm, 72mm, and 85mm XL Super-Plössls. Wow. Huh. Not that expensive.

And they note rule of thumb I briefly mentioned to Tony. It is suggested that you do not go below 35x in any scope that has a central obstruction. If your obstruction is larger than 25% of the primary, you could also get a "ghost" image of that secondary mirror.

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