The Sigma 28mm f/1.8 aspherical lens is the fastest 3rd party wide angle manual focus lens ever made and it is also the fastest 3rd party wide angle lens you can find in Olympus OM mount. According to the comprehensive list found here http://home.arcor.de/objektive/MFF.html the lens was made in 1992 and again from 1993-1995. This appears to be the first version of the lens made in 1992 only. A picture of the second version of the lens is below.
(some of the information is from the link provided) The lens is composed of 8 elements in 8 groups including at least one aspherical element. The filter diameter is 58mm with the lens barrel stretching to 70mm and an overall length of 57mm (2 1/4″). The weight of the lens is a solid 12.6oz. It has a minimum focusing distance of 1 foot (1:7.2 reproduction).
My limited time with the lens shows that it is very nice piece of glass. The focusing ring turns the opposite direction of zuiko (and most other OM mount) lenses, which can be a little annoying, but it generally doesn’t bother me. The aperture ring is snappy, but it doesn’t feel quite as smooth as my zuiko lenses. The aperture ring has stops at f/1.8, f/2 and then every half stop down to f/16. This lens does not feel cheap.
Focusing at f/1.8 isn’t that bad due to the depth of field of a 28mm lens, but it is still quite shallow and it takes a bit of getting used to having such a shallow depth of field due to the maximum aperature, especially if your only wide angle lens in the past has been an f/2.8 or slower. My only real complaint against the lens, it is a very minor thing is that the rear lens cap barely fits. Finding another OM rear lens cap would probably be a good idea, as the one that Sigma provided fits very poorly (hard to get on).
The lens seems relatively rare as I have only ever seen 4 listings, 3 for the first version and 1 for the 2nd version of the lens ever. Interestingly enough all the listings I saw over the course of about 3 weeks. Before that I had never seen or even heard of the lens despite spending about 2 years looking at ebay and other sites with some manner of regularity. So I am going to have to conclude that the lens is rare, but obtainable.
I found this lens on B&H’s website (where the comparison image of the 2nd version of the lens is from) and purchased it for a little north of $100. The couple of Ebay listings I have seen have gone from about $100 up to over $200 for this lens.
Update 5/22 – I managed to get a chance to really stretch the legs on this lens at my brother’s wedding recently. The lens is nothing short of superb. Most of the shots I was doing was wide open or stopped down possibly a stop or half a stop. There is no noticeable CA and the images appear sharp from center to corner. The shallow depth of field is useful as well. Below are a couple of the shots from my brother’s wedding that I took with the lens (they are scanned from the prints, so not perfect representation of what the prints actually look like).
Further Update – 10/14/09
I finally did some tests of the lens. I set it up on a tripod and took some pictures of an office desk at f/1.8, 2.8, 5.6 and 11. The following are the results from the center and edge of the frame at 100%. f/1.8 actually seems sharper then f/2.8, this could be in part because f/2.8 is slightly under exposed (by 1/3rd of a stop, since OMs can only control shutter speed by full stops it makes it hard to get bang on exposure without using partial aperature stops, and f/1.8 and 1/30s was the metered exposure), f/5.6 is a little sharper and f/11 is noticably sharper. That being said, even at f/1.8 things are resonably sharp, especially for being f/1.8! Very acceptable wide open (in fact very good wide open).
There is some evident CA that doesn’t seem to completely disappear even at f/11, though it reduces a bit. It isn’t anything noticable even in fairly big prints, but you can see a small bit of it at 100%. Ignore the slight color cast, no correction was done on any of the pictures (and no sharpening). Click on the center and edge picture for 100% size views. Though not a scientific test, comparing the Sigma 28mm f/1.8 test shots with the Zuiko 50mm f/1.8 MIJ test shots, the Sigma is at least as sharp at f/1.8 as the Zuiko is.
Center, from top to bottom f/1.8, 2.8, 5.6 & 11
Edge, from top to bottom f/1.8, 2.8, 5.6 & 11