First try with Sigma 70-200 mm f/2.8 EX DG APO OS HSM

[gorann]

I just bought this APO zoom lens for my Canon EOS cameras. I am going to use it for all kinds of photography but also thought it may be useful for AP since it is an "APO" lens with 70 mm aperture and contains two FLD (about the same as fluorite) elements within its 22 element / 17 group construction, alongside three elements made from the more conventional Super-Low Dispersion (SLD) glass. I all sounds very impressive but I have to say that my first attempt on AP with this lens is quite disappointing with very noticeable coma, CA and some odd light phenomena. I attach two pics. The first one on the Orion and Horse Head Nebulas were taken at 200 mm f/2.8 (a blend of 10 x 1 min at ISO 1600 and 10 x 2 min at ISO 2500 to balance the light intensity of these two nebulas). For the second pic (Pleiades) I attached a Sigma 1.4x APO teleconverter giving 280 mm f/4 (5 x 2 min ISO 2000), and there the coma is over the top (the focus is possibly not perfect but it was the best I could do on the 10x live view on the camera and that works well with my telescopes). Both taken with a Canon 60Da on a NEQ6 mount (did not bother with guiding due to the wide field and short exposures). I have done my best to stretch the pics and get the colours out but have not bothered with the vignetting.

My conclusion is that this lens is in no way comparable to a proper small APO telescope (like my ES 80ED). Indeed, the pics taken with the old Pentax Takumars I bought on e-bay (costing 1/10th of the Sigma) looks better, see this string:

http://stargazerslounge.com/topic/257080-imaging-with-a-101-dollar-lens/

Yes, I know that zoom lenses are not supposed to be good for AP but this is a rather expensive one designated to be an APO. Clearly, it would benefit from being stopped down but then it is not a 70 mm aperture APO anymore. I may try stepping it down and report as soon as the sky is clear again. My hope is that it will be excellent for daytime photo as i has got good reviews:

http://www.lenstip.com/263.1-Lens_review-Sigma_70-200_mm_f_2.8_EX_DG_APO_OS_HSM_Introduction.html

[Chris Hopson]

Well I'm very impressed with the first image, nice horse head.

I think the tamron might be sharper, but the sigma has the tele extender. A nice lens mate.

Regards,

Chris

[Knight of Clear Skies]

That's not bad for a zoom lens wide open. I'd give it a try at about f4, which is still fairly fast compared to many scopes.

Unfortunately most camera lenses are not designed to produce a flat field wide open and will require stopping down a bit. I've heard some people say that macro lenses tend to be flatter than normal ones.