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Originally Posted by [1ponders]
Hmmmmm...you might be pushing it a bit with those short eyepieces. Given the objective fo your scope then your max usable mag is around 200X (50X per Inch of objective. you can go more but resolution will suffer) So with a 2.5mm eyepiece that will give you 200X.
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Paul,
50X per inch of aperture is a general rule of thumb that usually can be applied to most general designs of telescope. In many cases it can easily be exceeded when atmospheric conditions are favourable. The telescope designs most able to exceed 50X per inch are 3" to 6" high quality apochromatic refractors, The Russian 5" and 6" Maksutov Newtonians and high quality reflectors with premium hand figured mirrors. In many cases these scopes can run to 65X or 70X per inch of aperture without image breakdown. Carl Zambuto "guarantees" his mirrors to "exceed" 50X per inch of aperture under favourable conditions as does Bob Royce.
The TV Genesis is a high quality 4" APO which uses an F12 primary doublet and another doublet at the rear of the OTA to reshape the light cone. It "should" do 50X per inch "on its ear" under reasonable conditions. The 2.5mm Vixen Lanthanum is one of the more popular planetary eyepieces in the TV Genesis giving 200X @ 50X per inch.
CS-John B