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While 170X is possible it’s rather more than 2x per mm which is really the practical upper limit for refractors and TBH 170x is hype.
I could push my 70mm to 300X with a 1.6mm eyepiece, but there’s no point.
Can’t beat the physics of diffraction.
FWIW APM have a large selection of small APOs available from 50mm up, and assorted focal ratios, some clearly aimed at imaging while others are dual visual/imaging, the difference being the backfocus and focusser travel. Another aspect for imagers concerns all-screwed adapter rings to connect a camera - far more precise and secure than a cheap slip-fit 2” adapter. Add to that availability of 2.5” or 3” focussers including tack & pinion types able to lift heavy loads securely.
Last edited by Wavytone; 09-02-2018 at 09:52 PM.
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