Canon EF 50mm f/1.8 II for astrophotography
Canon's EF 50mm f/1.8 II lens, despite having the build quality of a Pez dispenser, packs a good set of optics. And at about R900, it's not expensive.
The images below are crops from a sequence of images, at increasing f/stops, taken with alpha Centuari positioned at the extreme edge of the field of view. The reduction of coma and colour aberration can be followed as the lens is stopped down.
(left to right) f/1.8, f/2.8, f/3.5, f/4.0. All images taken with a Canon EOS 60D at ISO 1600, exposed for 1 second.
(left to right) f/4.5, f/5.0, f/6.3, f/7.1. All images taken with a Canon EOS 60D at ISO 1600, exposed for 1 second.
The image of the star at f/6.3 is pretty much perfect. The lens works just as good at f/5.6 (although I forgot to include it in this sequence!).
With the EOS 60D, this 50mm gives a field of view of 24.5° x 16.3° (image scale: 17 arcseconds per pixel).
nothing more to see. please move along.