visual art Planets, Astrophotography, and UV/IR Photography

[Phosphor 11,522]

Recently, I got a chance to image Venus in UV with my Skywatcher 16 telescope. I've been wanting to compare its UV performance with my Celestron C8. The Skywatcher 16 is a reflector design, while the C8 is a Schmidt-Cassegrain (see link for more info). It is known that reflectors perform better in UV than telescopes with glass in the optical path. There are several reasons for this:

1. Glass tends to absorb UV, especially wavelengths below 365nm or so
2. Glass lenses tend to display worsening chromatic aberration with shorter wavelengths

With the C8, I can get decent UV images, but the focus is never sharp. The glass corrector plate is designed to correct spherical aberration caused by the primary mirror, but the corrector plate simply cannot do this for the entire visible spectrum, much less UV. Also, the glass corrector plate absorbs some of the UV light passing thru, dimming the image on the camera. You can see the defocus around the planet's disk. Compare that to the Skywatcher 16, the planet is well focused.

This isn't a fair comparison tho. The Skywatcher 16 has a primary mirror of 16" in diameter vs 8" for the C8, yielding 2x the resolution.

https://en.wikipedia.org/wiki/Schmidt–Cassegrain_telescope

https://en.wikipedia.org/wiki/Chromatic_aberration

Hope you enjoy reading all of that.