The Sigma 400mm f/5.6 APO is my first rather expensive lens (about $300 from Ebay). I had originally been looking at and bidding on a black Sigma 400mm f/5.6 lens that had the auction taken down about a day before the ending. I was a little broken up about it and then I saw the auction for this puppy the same day. I had originally been wishing I could have gotten the one in black and I think black is a lot more low key, but in some ways the white kind of grows on you. I guess it is to much exposure to sports and wildlife photogs with their white bazookas that did it for me. Telephotos just seem to look better in white. Of course who cares what it looks like if it can’t deliver the goods.
The lens is quite compact with a telephoto ratio of .72. It is an internal focusing design with a 9 bladed aperature and an aperature range from f/5.6 down to f/22 in half stop increments. The lens has one or more low dispersion glass elements to reduce chromatic abberations (APO) and is arranged in 11 elements in 8 groups. It has a minimum focusing distance of 4m (13.3ft) with a magnification of 9.5:1. (field of view 6 degrees). The lens takes a 72mm filter, has a large built-in extendable lens hood and tripod collar. The overall dimensions of the lens is 85mm in diameter maximum and 212.5mm long (3.3″x8.4″) and weighs 960 grams (2lbs 2oz).
From what I have been told the APO version of the Sigma 400mm f/5.6 and the ATX version of the Tokina 400mm f/5.6 are significantly better then the regular Sigma 400mm f/5.6 and the base Tokina 400mm f/5.6 SL. Some tests awhile back showed the Sigma APO to edge out the Tokina ATX wide open and the Tokina edged out the Sigma when stopped down a couple of stops (and with an f/5.6 telephoto lens you are probably going to use it wide open or nearly so most of the time).
The lens appears to be pretty sharp wide open and stopped down just a bit. View the below sample imaged (prints scanned on an Epson flatbed at 350dpi).
For the fun of it I decided to compare this lens against my smallest lens (Zuiko 50mm f/1.8). I think the Sigma 400/5.6 edges out the 50/1.8 a bit.
Another view of the Sigma attached to the camera with hood extended (its big, not 400/2.8 or 600/4 big, but still big).
The can images were shot at 1/500s and f/6.3 and the dragonfly at 1/1000s and f/11 all handheld (I am getting better at that). On the negative of the one can (vertically oriented photo) you can read the barcode number on the beer can on the upper left magnifying the negative. You can’t read it on the scanned image of the print (the 4×6 print just doesn’t have enough detail).
A comparison of the Sigma 400mm f/5.6 APO at f/5.6 and at f/11, the test was done with the lens and camera placed solidly on a flat surface with mirror lockup (no remote shutter release however). The scan is from an Epson flat bed of the print at 350dpi and the comparison is 100% crop of the resulting image (not quite as good or high quality as scanning the negative, but until I own a good negative scanner this is all I can manage). As you can see the lens at f/11 is very, very slightly sharper, but it is a small difference.
Update: Since getting the lens I finally bought a halfway decent scanner (Epson 4490). At least decent enough for better scans, and of the negatives themselves. The version of the Sigma 400mm f/5.6 APO I have has a small amount of haze that does seem to impact contrast a little bit, but not by much (a slight 6-8% tweak to contrast in PS is enough to correct it). The lens is pretty sharp even wide open, but it seems best around f/8-f/11. Another example picture. The hawk took off before I get get any closer.