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Sigma AF 21-35mm 1:3.5-4.2 Aspherical
A first-generation AF ultrawide-zoom.
In fact the optical constructrion of this lens is the first ultrawide-zoom-lens, that has ever been built in the world, at least the first that could be regularily bought! When Sigma announced the construction of an ultrawide-zoom back in ... I think it was in the eighties, everyone just laughed. Nobody had built such a thing before and nobody believed, that such a lens could be any good. Of course it was a manual focus lens.
This lens here is the exact same thing as this very first ultrawide-zoom optically, just transformed to the AF era and with an electric aperture.
And guess what: People stopped laughing. This lens, and so the very first version back then, is actually very good, in fact it is better than many ultrawide-primes of that time. It's sharp, with even good extreme-corner-performance at 21mm wide open, has a relatively good CA and distortion-performance and is relatively fast, too. It even takes 77mm filters!
Of course, this AF-version has the worst AF you could imagine, as it's a first generation AF-Sigma: It's very loud, slow and sometimes inacurate.
But apart from that, this lens looks like Sigmas professional - grade lenses from that time like the 180/2.8 Macro or the 70-210/2.8 APO. It has a full metal body and feels very solid. But the focus ring turns during AF and it has some play. The lens seems tough, sturdy, but not at all big or too heavy.
Warning: This lens does only work wide open on digital- or newer film-bodies and cannot be stopped down, except for having been converted, which mine is.
This is a lens I converted for use with newer EOS - bodies. I did never need or want this lens. I just bought it when I saw a buy-it-now - auction on ebay, where it sold for € 25,- including shipping. I simply was too curious to pass on this. Well, my 19-35 is better and wider, so I never use it, it's a pure backup and one of my few collector's items.
COMPATIBILITY
As a classic EF - lens, it mounts on every EOS - body ever made, be it 35mm film, APS, digital APS-C or "fullframe". On APS-C, the smaller sensor of these cameras let's this lens have an angle of view like a 35-56mm-lens would have on 35mm, which is silly.
Warning: This is a lens from a time, when Sigma had reverse-engineered Canons EF - protocol wrong instead of licensing it. Therefore, these lenses DO NOT WORK with any digital or newer film bodies! On these bodies, you can only use such lenses wide open, the body cannot close the aperture and reports an "Error 01" or "Error 99". At the time this failure got evident, Sigma offered a conversion of the non-working lenses, but nowadays, they only do it for a handful, mostly expensive long tele-lenses, but not for this one any more. The only way to get a sample that works at any aperture is, that it has been converted by Sigma in the past or to convert it by yourself.
Excursus: Today, there actually and finally IS a way to convert these lenses by yourself, developed by two very cool members of the site "dslr-forum", nightshot and slein. It is based on a small (and cheap) micro-controller you first program and then solder "between" your lens' circuitry, cutting the original electrical circuits. I won't explain this further here and won't take any responsibility for anything you screw up trying this. Please search the internet, if you are interested. It really (really!) requires some experience in soldering (the parts involved are heat-sensitive and small!) and in using a computer on quite a low level: If you don't know, what a hex-code or a programmable fuse is: Don't do it! Having said that, I did convert several old Sigmas using this way and it really works. It doesn't work flawlessly, but it works. The problems are, among others, that you have to wait a few seconds after turning on your camera (or waking it from sleep) before you take the first shot, otherwise the aperture won't be closed. You still get Error - messages periodically, especially when pushing your luck e.g. by taking a longer series of images, stopping for a second and pushing the shutter again. Then you have to turn off your camera and turn it back on again. This can happen 3 times within 2 minutes or not happen for a hundred shots. This is still and will always be kind of a botch-solution, or at least a DIY-solution and a bypass, with a controller, metaphorically speaking, "stopping" a signal from the camera, "translating" it and sending a different one to the lens' electronics. And all that in the short fractions of a second between the signal sent from the camera and the lens having to have reacted by closing the aperture just in time while the shutter is open and all this up to 11 times a second on a 1D - body. That simply can't work flawlessly.
PRICE
Prices are extremely low. It's realistic to get a good but unconverted sample with very good lenses for below € 50,- including delivery. Many samples have problems with the AF.
ACCESSORIES
This lens doesn't need a shade, as it is built in and can't be taken off. I hate this, because it makes the lens bigger and I never use shades, but the good thing, I have to admit, is, that it protects the bulbed front-element and you always HAVE a shade - this lens is quite prone to flare.
It takes normal 77mm filters, but the filter-thread not only moves in and out, but also rotates when focussing, so using filters isn't nice.
MECHANICS
Made in Japan.
Metal lens mount.
Everything seems to be made of metal. The only thing made of plastics on the outside is the window of the focus - scale... and - of course, the miserable rubber-like stuff, the complete outer lens body is covered with on the old Sigmas. This rubber gets sticky and nasty with time an today, I can scratch it from the lens with my fingernail. *ughhh* That's not nice. I think it was supposed to have kind of an "outdoor" and "rugged" touch.
AF is slow, really slow and loud. This could have a good side in it, when that the "moderate" speed made the AF really precise - but it isn't precise, either. While always fine from 28-35mm, at 21mm, if it hits the point, it's great, too, nearly dead-on with all of my bodies. But it doesn't always hit the point. If you focus the same point without moving the camera several times in a row (just half-pressing the shutter a few times in a row), the lens sometimes changes focus EVERY time and the point 1m away is focussed at anything from 0.5m to 5m. By now, I can't say what's the reason for this, because I can't reproduce this: Sometimes it's really fine, sometimes it's not. Maybe some dirt somewhere between some contacts? I'll search on and tell you.
The inner mechanics of this, as well as of most Sigmas of that time, are generally "tank like" also, best described as "down-to-earth" or "low-tech". Cables are thick, screws are solid and the barrels are made of metal.
All in all an impressive lens. It's a bit like I imagine old russian technics to be: Always something to take care of, but if you do so, built to survive a nuclear war.
ERGONOMICS
Very good. It is small and light for a full-metal-lens, but heavy compared to a plastic 19-39. It handles quite well. I hold it right intuitively, gripping it exactly right to zoom.
Manual focussing is a real pain, because the "focus-ring", if you want to call it like this, actually is the front-element with a small and tight rubber-ring around it. To turn it, you have to get your fingers between the elements of the shade and try to fumble the ring in one direction or the other. It's even hard to find the ring, but turning it it horrible, you can't even use two fingers of the same hand.
This lens feels massive, solid but "low-tech" and comparitively small. Size DOES matter, also see Lenses: What's important?. You can hold a body with this lens in one hand. It fits everywhere for transportation and because of it's metal body and low price, you can jam it in any bag or rucksack you take with you.
The focus-ring is a bit too loose and undampened. Of course it has no instant manual override. To switch between AF and MF you have to turn a switch near the mount.
There is a focus-scale without infrared-focus-indices but with a depth-of-field-scale for 21mm and 35mm.
OPTICS
Optics of this Sigma are great.
The minimum focus distance is 0.5m, which isn't good, but hardly close enough.
Distortion is as expected, from quite obvious barrel at 21mm, about neutral at 28mm and a bit pincushion at 35mm, but on a low level for an ultrawide! In fact old 14 or 18mm primes, or a Canon 24-105L, have a lot more distortion. This shouldn't be problem when not shooting brick-walls. The plane of focus is bit curved outwards, you have to focus a little bit closer to get the borders in best focus - not unusual for an ultrawide, but annoying..
Vignetting is really bad at 21mm and eases when zooming in or closing the aperture. At 21mm wide open it is surely above 3 stops darker, what is bad, because the darker area is comparitively small and therefore fades quite rapidly. It really has that "black corners"-look. As with my other converted Sigmas, there's so few valid information abot these lenses online, that I provide some samples:
The aperture is made of 6 blades, giving you not-so-smooth bokeh and out-of-focus highlights with boring 6-ray-light-stars. OK, bokeh surely isn't a main application of such a lens, but nonetheless not good.
I have no information on this lens' usability for for infrared-photography, sorry.
While I think, that a lens less prone to flare and especially ghosting is not always better, as at least ghosts can be a very nice tool to show the lighting conditions in your pictures, this 21-35mm flares more than newer lenses. Not really bad, but with a possibility not only to show some greenish ghosts, but to "glow-out" the whole image, when you have very bright lights like the evening sun at the border of the frame. Gladly, lamps, the moon, candles or similar light-sources in the dark aren't a problem and you can always avoid it by changing the angle a bit and remember, that you always have the fixed shade with you, so a maximum shielding-effect is always present. Not as bad as some old manual wide-angles, but still worse than newer constructions.
My samples color reproduction has that a little bit warmer overall cast, old Sigmas sometimes show. That's irrelevant on digital, but I'm still not sure, where this comes from.
Lateral CAs (purple/green fringes along high-contrast edges) are comparitively well controlled for an ultrawide, maybe with a maximum width of 1.5 pixels, I'd estimate.
Sharpness is one of the most overrated qualities of lenses. That being said, this lens is always sharp in the center and has very good corners, too, surprisingly, and especially so for an ultrawide. Zooming towards the 35mm-end lowers overall sharpness a just a tiny bit, but makes the image even more uniform. This really is an extremely good performance, no Canon ultrawide-zoom comes only near this sharpness-level!
It would be extremely boring to show you dozens of sharp 100% crops, so despite the fact, that there is hardly any valid information about this lens on the web, I'll show you just one single 100% crop from a 21MP image from my 5D Mark II:
21mm, f/3.5! This is from the extreme (!) top-left corner. If a lens is this sharp at it's worst possible setting and position, I won't bother you with other test-shots. It's only woth mentioning, that this image gets really blurry just beside this crop, because of field-curvature. the other alternative is, to have the rest in focus, and this corner not. Use f/8 to deal with this, if you need a uniform, flat brick-wall ... or simply don't care about it, if you're a photographer, and use this lens like you would do instinctively.
Alternatives
There are a lot of alternatives. This lens' main drawback, apart from having to be converted to be used on digital, is, that it isn't very wide by todays standards and that it's construction is old, with all the consequences like AF-speed and accuracy, noise, and so on. All alternatives are better in this regard but only very few are optically.
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