leon pugh , August 23, 2008; 03:49 A.M.
I had the chance to test both a Sigma 300mm f2.8 (APO EX DG) and the Sony SAL300f28G (300mm f2.8 G Lens)
The new sony lens uses a SSM focus motor built into the lens. It is fast and quiet. Unfortunately my Sigma 1.4x teleconverter (the EX GD model) does not work with the Sony lens. The autofocus does not work (and trying to drive it with AF on the Sony lens on might actually be bad for the camera or at least the batteries). The comparison test was done without the teleconverter.
For the side by side tests, I had both lenses at a retailer and for a test target I used of a colorful brochure, a slightly frayed pigeon feather (texture/detail) and black on white text (contrast/ Chromatic abberation). Images taken with the Sony lens at f4 were sharp. There was no chromatic abberation or hint of red/green fringes around the text. Images taken with the Sigma lens at f4 were not as sharp. Some text had a slight red-brown fringe on one edge, contast was less defined due to the slightly fuzzy edges. The Sigma lens DID give a brighter image at f4 than the Sony lens. I got the impression that there was a hint of CA on the Sigma lens, by just imaging black text on a white page.
An image of a car parked outside gave noticeable CA off of some of the glare with the Sigma lens. A photo taken with the Sony lens at a leter date did not show any CA.
I later tested the Sigma (alone) with point light sources (stars) and I can say that there is some chromatic abberation. Star images started to look good at about f5. Any wider and the C.A. got progressively worse. However, most lenses are not made for astrophotgraphy but I do own a few lenses that do better that the Sigma 300 f2.8. My Sigma 70-200mm for example give very good results at 200mm and f3.5. I checked some review sites for the weight of each lens. The Sony lens is listed at 5.1 lbs. The Sigma is listed at 84.7 oz. That converts to 5.3 lbs.
I wouldn't want to use the Sigma lens for anyhting requiring alot of fine detail at anything wider than about f 5.
I decided to buy the Sony lens. I have been surprised at seeing some very sharp images with the Sony lens even at f3.5. I have not tried to push it any lower yet. I tried it as the kind os test you expect the lens to fail. If I knew how good the resulting image was when I later viewed it on my monitor, I would have tried the test at f2.8! I have not noticed any chromatic abberation yet with this lens, but I have not been shooting with the effort of causing it. The Sony lens has done much better on targets that would have caused some CA fringing on the Sigma lens.
I like the ability the SONY lens has for selecting what range/ranges of focus you want to use. You can have full range, partial (about 6 meters to infinity), and user defined where the user sets the far focus point and the near focus point. This last one is VERY useful for shooting in the bush with all the trees and close grasses and branches that may come between or behind your target.
With the Sony lens costing about $ 4,400 Canadian more than the SONY lens, making up your mind is easier. Need a new cheap 300mm f2.8 prine lens? Buy the Sigma (or if Tamron/Tokina make one try theirs). You might even do well with a good zoom lens somewhere in the range of 70-300, f4.5. At least it will be lighter. I think the Sony lens is amazing. I have used it on 2 outings now and am VERY pleased with the results. It is better than my 70-200mm Sigma f2.8 which until now was my best "long-walking around lens" lens for sharpness, contrast and lack of CA.