Quote:
Originally Posted by bojan
I have a similar one (Tamron 400mm f6.3), I got it locally for $30..
It is a Tamron, but no good at all.
But for guiding (and terestrial probably), it's OK.
It seems the optical quality of those lenses are all over the place.
http://www.iceinspace.com.au/forum/s...ight=f6.3+lens
I removed the field lens group (the one closest to camera) and it become ~300mm..
Could you do some tests on stars? Middle, of the frame, corners.. |
Well, as a lens that doesn't start to shine before f8, I never really intended it for astro. Although... how nice would 350mm be for the Helix! If I throw it on the back of my tracking newt rig Bojan I may give it a try. However, none of these lenses are good enough for astro, that's why we have to spend at least $500 on an apo.
But it's an old achromat, I think the stars will punish it. I'd expect aberrations like coma to be reasonable, lenses like this are flat, coma should be expected, but ca, dunno, the stars will punish it.
Here is a 100% crop of a contrasty scene to give an idea- CA is not bad in the center but from 50% out becomes more noticable. No corrections in LR6.3 RAW conversion, and neutral sliders all the way down.
Fact is, we have to buy better optics for astronomy, at least one ED element. My Fuji XC50-230mm exhibits remarkably well corrected images and it has one ED element. It cost $200 on special.