Since I bought my 17.5" reflector, I have made little use of my 5" refractor or my 8" reflector. I rolled out the refractor Friday night and looked at the Moon. I had forgotten how well this Photon Instruments 5" achromatic refractor combined with the Chromacorr corrector works! Color free even on the Moon at 493x!
Ordinarily an achromatic refractor starts to become useless at high magnification on bright objects, because the red and purple fringing destroys detail. The Chromacorr corrector is a product caused by the collapse of the Soviet Union. The designer is a Ukrainian who worked in their weapons industry. This incredibly cool product goes between eyepiece and objective, effectively turning an achromat into an apochromat. Compared to a 6" Astrophysics apochromatic refractor I used at a star party some years agoside by side with this hybrid, mine was only slightly worse on color and image quality. The Astrophysics was about $6000. My achromatic refractor cost $375 used; the Chromacorr was about $600.
There is a rule of thumb that most telescopes are practically limited to 50-60x per inch of aperture. This is both a limitation of the average telescope optical quality and atmospheric turbulence. Really high quality optics like the Questar and Televue can go much higher. By that rule, a 5"refractor should go usefully to 250x-300x, but this does much better.
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