I own two Unitron 40mm, F/17.5 refractors, including a very early example I recently acquired from Dave Trott. Both produce beautiful images for their size and I have had a lot of fun using them.
I find that the challenge of finding and observing my favorite celestial wonders with these tiny instruments has made my nights under the stars fresh and new again. Most objects look much different than through my larger telescopes, and it is almost like seeing them again for the first time.
I recall several earlier threads where some owners of these little guys found the optics to be less than stellar, so I set up my DPAC rig to see for myself.
On my two examples, at least, the lines are ruler-straight and thus indicative of excellent spherical correction. And at F/17.5 for a 1.6" aperture, color is obviously not a problem.
Under dark skies, brighter double stars look wonderful due to the large Airy disks, and I even saw a little detail on Mars during last year's opposition. Saturn's rings and a couple of Jupiter's belts are duck soup in these tiny marvels. And most of us are aware of the striking, seeming 3-D images of the moon such small telescopes can deliver.
Anyone who has not observed through a diminutive refractor may find, as I did, another dimension to this hobby of ours!
Edited by Steve Allison, 09 January 2020 - 11:01 PM.