02-07-2013 08:07 PM
Which is better for astrophotography,
a Canon 70-200mm lens with a Canon Extender EF 2X III or Canon 100-400mm lens
If you refer to Canon 70-200mm 2.8L IS II USM + Extender 2x III, then you'd get f/5.6 all over the focal length range vs. the EF 100-400 f/4.5-5.6L IS USM (meaning you'll get a bit more of light at the short telephoto end when using the 100-400)
Both combinations are very sharp, but I think the 100-400 is a bit sharper when compared to 70-200 2.8L II + extender 2x III, noticeable if you use full frame DSLRs.
If you use APS-C DSLRs, then I'd suggest going for the 70-200 2.8L IS II USM because you'll get more than 1 f-stops of light if you shoot from 70 to 200mm (without the Extender 2x III) compared to the 100-400, and the sharpness is really amazing (better than 100-400 in both Full Frame and APS-C cameras)