Sigma 28-70mm f/2.8

I received this lens as a slightly early birthday present. Its quite a bit of fun to use as I am not used to anything in the wide to portrait length being this fast since, at least as of the time of writing this, I don’t have even a variable aperture wide-portrait zoom with an f/2.8 wide end. The Sigma 28-70mm f/2.8 isn’t quite as advanced as a few of Sigma’s other offerings of the time as it does not incorporate any APO elements.

The lens is a two touch design with a wide focus ring and a narrow zoom ring both with easy to grip texturing common to most of Sigma’s offerings in the early to mid ’90s. The lens is also, unfortunately, not an IF design like their 70-210mm f/2.8 is, so the lens expands on zooming and focusing and the front element rotates on focusing.

So with the ‘bad’ out of the way as it were, here are the actual statistics and some of the good. The lens has a zoom range from, as you may have guessed, 28mm on the wide end to 70mm on the long end and a fixed aperture of f/2.8 with a minimum aperture of f/22 with clicks every half stop on the aperture ring. The lens has a 72mm filter size and a minimum focus distance of .5m for a reproduction size of 1:5.9 at 70mm. The lens is composed of 13 elements in 10 groups, a maximum diameter of 75mm and a length of 92mm at its shortest. The lens weighs in at 553 grams for a bit of heft, but really not that bad. The lens was produced from 1992-1995.

The lens is at its shortest at 60mm and infinity and it extends slightly zooming to 70mm, only a couple of mm. At 28mm it protrudes quite a bit and of course if you zoom to the closest focusing distance it extends to its maximum then.

The lens handles fairly well and that bright aperture is definitely nice, for DOF and for shutter speeds. That being said I think I am prime spoiled. With a 28/1.8, 50/1.4 and an 85/2 the zoom just feels a bit out classed. The lens does make a good walk around lens, so long as you don’t need anything really compact. That or if you are limited in your ability to change lenses either because of the time it takes or the weather (dusty, rain, etc). With film since you can’t just crank up the ISO whenever you need its nice to have fast glass on the camera if it is the only lens you are going to use.

I did some test photos of the Sigma 28-70mm f/2.8. The test was conducted using more or less the same target that I’ve used for a few other lens tests, a bookshelf with some of my son’s books on it. I did the shots tripod mounted with mirror lockup and I moved the camera between zoom settings to maintain approximately the same field of view. This time around I did both center and corner tests instead of just center. End result, the lens is sharpest at 70mm and its rather soft wide open. Detailed test results below. Click on any of the images for the full resolution image.

Click on the photo for a 1000 pixel wide example. This is at 28mm and f/2.8, basically the softest setting, especially in the corners. Its not a full res version of the 3200dpi scan, because frankly I don’t have the kind of image storage space to be throwing up 8 meg Jpegs willie nillie. It does give you a reasonable idea of what an 8×10 would actually look like. A little soft, but not horribly objectionable/unusable.

Center tests

@70mm f/2.8, f/4 and f/8 respectively

@40mm f/2.8, f/4 and f/8 respectively

@28mm f/2.8, f/4 and f/8 respectively

Conclusion: As you can see at f/2.8 at all settings its soft, at f/4 it sharpens up a lot and at f/8 it is just a bit sharper. All zoom settings are fairly equal in the center, but I feel that 40mm edges out the others by just a bit.

Corner tests

These crops are from the top right corner.

@70mm f/2.8, f/4 and f/8 respectively

@40mm f/2.8, f/4 and f/8 respectively

@28mm f/2.8, f/4 and f/8 respectively

Conclusion:The lighting didn’t really help with the corner tests as they get progressively darker as I zoomed out and moved the tripod. That being said 70mm definitely wins out here with 28mm being the softest (it is exaggerated a bit by the poor lighting, after all lower contrast equals lower resolution). I’ll have to come up with a better way to light things the next time I run a test so that the lighting remains equal in each shot.

Overall conclusion: At 70mm the lens is at its sharpest except in the center, but it is only a hair softer in the center whereas at the corner it is much sharper then the other settings. In the center things sharpen up a lot at f/4 and a bit more at f/8. In the corner things sharpen up some, but not as much at f/4 and at f/8 there is more improvement then there was in the center going from f/4 to f/8.

The lens is soft wide open, but unless your doing 13×19 prints it is still quite usable even wide open. Once you stop down a stop, or especially two the lens is quite sharp and you aren’t likely to notice any softness in something like an 8×12. Wide open you’d probably notice a slight softening wide open in something like an 8×12, but again perfectly usable wide open.

For the $130 I paid for the lens it is a good fast wide to portrait zoom and if that is what you need in OM mount, your choices are pretty limited. I’ll try to get a test of the Tamron 35-70mm f/3.5 in soonish to compare to the Sigma 28-70 f/2.8 even though they don’t cover exactly the same range or aperture. My gut feeling is the Sigma is at least as sharp at all of the apertures that the Tamron can match and has the advantage of going 2/3rds of a stop faster and 7mm wider.