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Ed,

Measured the length of the 22x70's to be 15 7/8" with the eye cups rolled down. The eye lens was recessed ~3/8" and the edge of the objective was recessed 7/8" with the dew shields retracted. That leaves ~ 14 5/8" from end to end. With the eye cups and dew shields extended the total length is 18 3/4". The focal length should be ~ 16.5". I'm guessing 20mm FL (0.8")eyepieces.


Do you think the prisms path can account for the ~ 2.7" difference? Still seems pretty close to f/6.

Peter

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typical prism light path can range from about 80mm for very small prisms up to about 120-130mm for very large prisms. Focal length thru the prisms is light path divided by index of refraction, so the prisms can reduce the overall length by 80/1.56=~50mm to about 130/1.56=~80mm. F/6 works out well.

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