Petteri's Pontifications
My musings about photography, mostly.
RSS feed
Practically A Prime: The Sigma EX 12-24/4.5-5.6

Practically A Prime: The Sigma EX 12-24/4.5-5.6

Wide-angle has been the only area in which I've found the Canon EOS-10D system significantly lacking. The "crop factor" means that reaching even fairly common fields of view, such as 28 mm equivalent, involves significant compromises, and fun focal lengths much wider than that are much more difficult. That's why I was awfully excited when Sigma announced the 12-24 zoom -- and awfully disappointed when the first comments and test shots I saw were less than flattering. However, I ended up buying it anyway: some of the samples I saw appeared to show no major lens boogers, and I figured I could put up with some just for the possibility to get 20 mm equivalent, or thereabouts.

Popeye ready to go on the EOS-300D.

The Sigma EX 12-24/4.5-5.6, hereby christened "Popeye," because of its bulgy front element, occupies a unique niche among lenses. It's the first rectilinear 12 mm lens designed for 35 mm SLR's (yes, it's full frame). In fact, I believe it's only the second 12 mm rectilinear lens for the 35 mm format. The first was the Voigtländer Heliar ultra-wide 12/5.6 -- considered remarkable enough to rejuvenate an entire lens mount (Leica M39). This is something to keep in mind for the folks who gripe that Popeye isn't too bright. In other words, it breaks very significant new ground by the simple fact of existing.

Since the 14 mm rectilinears from Sigma, Canon, and Tamron are optically somewhat disappointing for the price, Popeye's only real competitors for ultra-wide with the APS-sized DSLR's are the "diagonal fisheyes" from Canon, Sigma, and Zenitar (not counting the Nikon 12-24 DX lens, which I've long been jealous about). These are smaller, brighter, cheaper, and optically excellent -- but unfortunately de-fishing them involves losing a good deal of resolution, gives a wider format to the image, and makes accurate framing difficult since the viewfinder no longer matches the final picture. Of course, you might not always want to de-fish; there's something to be said for the creative uses of the fisheye look.

Mmmmm... ultra wide.

Popeye only goes to 24 mm (38 mm equivalent). This makes it a rather a different beast from the other wide-angle solutions, the 17 or 18-to-something zooms, which come close to replicating the 28-to-short-tele range of classic 35 mm "normal zooms". It's a dedicated wide-angle instrument: in its uses, practically a prime.

Design and build

Popeye is significantly more compact than its elder sibling, the very highly regarded EX 15-30/3.5-4.5, although it weighs about the same, and balances very well with the 10D. It's somewhat bigger than the Tokina 17/3.5 it's replacing, but still a manageable and reasonably portable size; in fact, my first thought when opening the box was "it's smaller than I thought."

The zoom and focus rings have no slop and feel very tight (the zoom ring maybe even a bit too tight; it might loosen up in use, though). Throw on the zoom ring feels "right" -- easy to go from one end to the other. Throw on the focus ring is maybe a bit too long. DOF markings are present but not great -- only for f/5.6 and f/8, not compensated for focal length changes. Interestingly, it appears that the Minolta and Pentax variants have better DOF markings: I wonder why?

The AF switch is well positioned; easy to switch with the thumb even with the camera to the eye: a very nice ergonomic touch. Because of the HSM, the MF ring is constantly engaged (FTM).

The lens barrel and markings.

The built-in hood looks largely symbolic; its main function is probably to protect the pop-eyed front element rather than help with flare. The lens cap only goes on with the weird slip-on metal ring thing, which seems like a bit of a kluge, although works well enough. (Why didn't they just make a lens cap shaped like a bucket?)

There are no rattles or squeaks. Finish is very good: markings are neat, paint is even, no manufacturing artifacts on any of the parts. The rings feel "dry" like on most AF lenses these days (Tokina AT-X Pro being a notable exception). Look-and-feel wise, Sigma EX is really giving Canon L a run for its money these days: everything about this lens cries "Pro lens!"

The HSM motor is silent and appears fairly fast. The lens focuses accurately up to about 2 meters: hyperfocal distance wide-open is about 1.6 meters, so much beyond that, there's no way for the AF to tell how far the subject is. In other words, for situationals with close-up subjects, use AF, but for landscapes and architecture, zone focus manually. The HSM is a nice touch, although in my opinion a luxury rather than a necessity at this focal length: FTM isn't really useful as you have to take the camera off the eye to zone focus anyway.

Popeye is internal focusing and sort of internal zooming, too -- the front element does move back and forth, but it moves inside the lens barrel. If only there was a way to use a lens-front filter with it, it would probably be pretty well protected from the elements. Unfortunately, you can only use gel filters with the lens -- the pop-eyed front element sees to that.

Optics

Given all the griping about Popeye's eyesight on DPReview, I was quite positively surprised by it -- at least on the 1.6x field of view crop. I'll put some film through my EOS-650 one of these days, just to take a peek at the corners. Even wide-open, Popeye sees enough detail to produce very nice 11 x 14 inch prints: this is quite a good achievement. The image holds together respectably well at all apertures and focal lengths. You can detect all kinds of interesting gremlins if you magnify to 200% and really look for them, but they're kept pretty nicely in their cages: nothing in particular jumps out at you. Some softening towards the corners is discernible at all focal lengths less than two stops from wide-open, but less than I had feared. There's very little CA for this type of lens, and extremely little distortion.

Stopped-down to f/11, the lens is impeccable: the optical quality should satisfy even the most critical of photographers.

Sharpness

It's interesting how deceptive "feelings" can be. I had already mentally framed a paragraph explaining that clearly the 12-24 was designed for maximal sharpness at the expense of contrast, not like the good old days, and so on. Then I started examining two frames I had shot within minutes of each other of the same subject, one with Popeye, the other with "Canon's best prime," the 50/1.4 USM. Both lenses were stopped down to their respective sweet spots. I was rather surprised -- there was very little difference between them. At its best, the Sigma clearly packs a quite a wallop in the sharpness department!

At top, a 100% crop from the Popeye at 14 mm, f/16. At bottom, the 50/1.4 USM at f/5.6. If you look closely, you will see that the 50 is just a tiny bit sharper and just maybe a little bit contrastier, but so little it could actually be in the eye of the beholder.

Center sharpness is impeccable at all apertures and focal lengths: the lens easily outresolves the sensor. Sharpness fall-off towards the corners is discernible until approximately two stops down from wide-open, but IMO the fall-off is pretty negligible: less than I had expected for a lens this wide. The fall-off affects contrast more than resolution, and is at least partly caused by vignetting. It responds to post-processing very well: a simple curves or levels tweak with a radial mask will improve the corners a great deal, and a similarly masked application of unsharp mask will almost erase the effect of the contrast fall-off (see Appendix below). An exceptional 20 mm prime on full-frame would do somewhat better, but not by much.

Wide-open at 12 mm, center of frame.

Wide-open at 12 mm, corner.

Two stops down, the lens is very sharp. I'm going to absolutely love shooting off-the-tripod landscapes with it. :-)

Stopped-down to f/11 at 12 mm, center of frame.

Stopped-down to f/11 at 12 mm, corner.

Interestingly, the lens maintains its characteristics very constant through the focal length range: the sharpness fall-off is very similar at 12 and at 24 mm.

Wide-open at 24 mm, center of frame.

Wide-open at 24 mm, corner.

For the rest of the sharpness test shots, see this page.

Chromatic aberration

Very positive surprise here: for CA, the lens is just about as good as any zoom I've seen, and better than some primes. I did catch one pretty clear instance of transverse CA (shiny object on a dark background near the edge of the frame), but I suspect it would take an 11 x 14 print to show it. In my CA test shots of branches against the sky, I had to blow up the picture to 200% actual pixels to be able to easily see the CA. This problem is kept well under control.

CA test shot: wide-open, corner of frame, slightly misfocused. Not bad.

Worst case of transverse CA I've seen in my RL shots.

Halation

The mystery of the "soft corners" explained: the lens is prone to a certain amount of halation wide-open near the edges. If you get a dark, sharp edge near the corner of the frame, you will get a noticeable "light spillover" that will decrease contrast and give an appearance of softness. Most lenses do this wide-open, and this one isn't particularly bad (e.g. the 50/1.4 does this noticeably more; of course, this is long gone by the time it hits f/4.5, though). I wonder what causes this, though? I'd guess comatic aberration...

Vignetting

Senate Square with tractor. 12 mm f/4.5.

Vignetting is noticeable if you have large, evenly lit areas in wide-open shots. However, it's nowhere near objectionable enough to make you want to use radial ND filters (good thing too, since there's no filter threads; I've no idea if you could make a gel filter like this either). In a more "chaotic" picture, the vignetting is completely unnoticeable, as it's overwhelmed by the lightness differences in the scene.

Distortion

I'm quite impressed by this characteristic: there's barely any distortion to be seen. Yeah, you can see it if you go through the trouble of shooting a rectangular object exactly at right angles and then using a straight reference to measure it, but at least I didn't notice it without jumping through these kinds of hoops. Distortion is well below my "noticing threshold" at all focal lengths.

There's the barest hint of barrel distortion visible at 12 mm -- a very good job, considering the field of view. I suspect you wouldn't spot it even on a picture like this if you weren't specifically looking for it.

Flare

My first flare test shots on slide were rather promising: Popeye appeared much better than I had expected, given the symbolic hood and bulgy front element. With the sun in the frame, one noticeable (and hard to clone out) flare spot showed up, but contrast loss was negligible. The flare spot was situated right on top of the sun, meaning that it would not have had a major impact on the "crop factor" area. With the sun just out of the frame, there were no distracting flare spots, and contrast loss was still very reasonable.

A flare "torture test." If anything, this situation should produce flare spots. There's only one really nasty one that I can see, and that's right on top of the sun. (Wide-open at 12 mm on Provia 100F.)

A second frame shot seconds afterwards, with the camera moved so the sun is just outside the frame. No distracting flare effects that I can see.

However, some further experimentation revealed that as I had originally expected, the lens does struggle with flare in strongly back-lit conditions. However, it is somewhat unpredictable, possibly because of the geometry of the pop-eyed front element: on some frames, flare is kept very well under control, while on others, it goes pretty much all over the place.

"Meditating," Helsinki, 2004. A tough situation for any lens to handle: directly into the sun. Not entirely unexpectedly, Popeye struggles: there are pretty obvious flare spots and other artifacts, plus significant contrast loss, although the contrast loss is largely restricted to the area around the sun.

It's pretty clear that I'm really going to miss the marvelous flare characteristics of my other wide-angle, the Tokina AT-X Pro 17/3.5. I haven't managed to get into a situation with it yet that would cause flare bad enough to seriously degrade the image. Looks like I'll have to learn to be more careful again, if the Popeye does become my primary wide-angle lens, as it's set out to be.

Phoenician seawall in Batroun, Lebanon. I shot this one with the Tokina AT-X Pro 17/3.5. I've done nothing in particular to get rid of flare effects, because there's very little that needs to be done: if you stare hard enough, you'll find a few faint, largish flare spots, hardly any contrast loss. I will miss the Tokina.

Color

I compared Popeye's color rendition against the 50/1.4 USM -- I undestand the same lens Canon uses for color comparisons. It did extremely well. There's the barest hint of a warm cast; even side-by-side, it's barely above the threshold of detection. In other words, the lens is as close to neutral as any I've seen -- no "Sigma yellow" problem here.

Fishing through ice. Popeye above, Canon below, with identical post-processing. There is a color difference, but it's tiny.

Performance on full-frame

I put a roll of Provia 100F through my EOS-650, with the lens locked at 12 mm. I used it mostly wide-open and stopped-down to f/11, plus a few interiors off a tripod at f/22.

The perspective is wild. This field of view is immensely fun to work with, although I'm sure it would take a lot more than one roll to properly get the hang of it. However, the visual effect of the 122-degree field of view is very striking, to the point that (much like a fisheye), this is likely to be the first thing that a viewer notices about pictures shot with the lens. In other words, it's hard not to make the pictures look "gimmicky" -- although it's clearly possible, going by some marvelous work I've seen done with the Cosina-Voigtländer Heliar 12 mm 1:5.6.

Helsinki Cathedral.

Interior of Helsinki railway station.

In interpreting the results for full-frame shooting, keep in mind two things to put the results into perspective. One, this angle of view is truly extreme. In a very real sense, it's pushing the envelope for the lens mount diameter and format in use; as mentioned earlier, Popeye is the first ever 12 mm rectilinear for SLR cameras, and only the second for 35 mm film -- and that CV 12/5.6 isn't without its problems either. Two, the crops below are from slides scanned at 2820 dpi -- that is, something like 10 MP images.

But enough disclaimers: let's look at the performance.

Sharpness

Contrast fall-off towards the corners is a good deal more severe than with the "crop factor." I haven't found high-resolution scans of the CV 12/5.6, so I can't tell how the Sigma compares; according to the reviews, the CV is supposed to be quite sharp at all apertures, so I assume the Sigma would be somewhat worse in this respect. The contrast fall-off is easily noticeable still at f/11, but goes away almost completely by f/22.

A center and corner crop at f/11.

A center and corner crop at f/22.

Vignetting

The laws of physics say that some vignetting is unavoidable at this focal length. In fact, vignetting is considered the largest flaw of the CV 12/5.6. The Sigma appears noticeably better in this respect: while vignetting wide-open is severe enough to cause a problem for slide shooting (since it easily puts the corners onto the "toe" of the film's tone curve, which further aggravates the contrast loss), it is much mitigated by f/11, and as good as gone by f/22. (According to the reviews I've read, the CV vignettes at least somewhat at all apertures.)

Vignetting wide-open. I wouldn't recommend shooting slides wide-open (unless, of course, you're specifically looking for this type of effect), although this degree of vignetting is no problem with neg (nor, I think, full-frame digital).

So, what does this mean?

Well, it's not as good with full-frame as with the crop factor. No big surprise: a 20-40 mm is no big deal, while a 12-24 is unheard-of. However, in my opinion, it's still more than good enough for street shooting, and stopped-down to f/22, excellent for landscapes. In other words, with full-frame, you'll have to take into account the lens's performance when taking your pictures: this is totally not a point-and-shoot device. However, if you play with it, you can get excellent pictures out of it even at full-frame. The focal length is immensely fun, and immensely challenging -- although the effect is something I wouldn't want to do for all of my shots. Still, the full-frame performance is clearly more than symbolic: Sigma meant business when making this lens.

Interestingly, to my eye it looks as if the vignetting and contrast fall-off start pretty abruptly somewhere around the 1.3x crop factor line. It would be very interesting to see how Popeye does on a 1D.

Conclusion: What's It Good For?

This lens should absolutely shine in architectural and landscape photography: off a tripod and stopped down to f/11, I expect nothing short of superb results from it. Its major limitation for situational photography is brightness and the intimidation factor: having Popeye shoved into your face must be a bit disconcerting, and f/4.5 isn't that bright (OK, it's pretty dark, really). Of course, the short focal length means that the lens can be hand-held pretty consistently at shutter speeds as slow as 1/10, which does help -- and of course the high-quality ISO800 and ISO1600 on today's DSLR's go a long way to making up for the dark lens. It's barely usable in poor indoor lighting -- crank the camera up to 1600, and usable pictures do come out. Still, this wouldn't be my first choice for available-light situationals. In fact, I think the Sigma 20/1.8 would be a very nice companion for Popeye -- reasonably wide, optically excellent, and bright as they come.

Popeye working the streets. The great hand-holdability that comes with the short focal length and is helped by the lens's heft is a major advantage. However, this is not a low-key, discreet lens like the Heliar 12/5.6.

With film or full-frame, Popeye is very much a "specialty" lens: the focal length guarantees that much. As such, it also demands special care and special skills from the photographer -- it won't give you fantastic quality at all apertures, but it can give you excellent quality and unique creative options, if you work with its strengths rather than against its weaknesses.

I get a feeling that Sigma did their level best with this lens. For crop-factor DSLR's, it's definitely a winner -- it's hard to see what Sigma could have done better, within the constraints of today's technology and the design decision to keep in the corners. Especially for people with a "slide shooter" mentality -- that is, who like to frame as precisely as possible in the viewfinder -- it looks a lot like the only choice for serious wide-angle work on these cameras. (Of course, the diagonal fisheyes are the other choice, but the problems with framing a to-be-de-fished image aren't trivial, and the loss of pixels hurts too.)

For full-frame, film or digital, the lens takes on a very different character. The extreme field of view gives unique creative options, but the difficulties of making a lens this wide become evident, too. For photographers who aren't familiar with wide-angle techniques and the problems inherent to wide-angle lenses, it would be a frustrating and possibly disappointing experience. For photographers who do have a taste for the unusual and the technique and understanding to work with the lens (or the willingness to learn it), the Sigma is a highly unusual, challenging but rewarding acquaintance.

Statue of Tsar Alexander III at Senate Square.

All in all, I have slightly mixed feelings about Sigma's design decision to make the 12-24 a full-frame.

On the one hand, I salute their courage: pulling this one off as well as they did should earn Sigma a place among the first tier of lens designers, right next to Canon, Nikon, Zeiss, Leica, and what not: after this, nobody has any business to talk of it as a cheap-o "third party" substitute manufacturer for "name brand" lenses.

On the other hand... well, I did buy it for my crop-factor DSLR, and I think so will the vast majority of Sigma's customers. And I think I would've gotten more for my money if it had been an "honest" crop factor lens, but, say, a stop faster, 2 cm shorter, 150 g lighter, and $100 cheaper. Of course, if it so happens that full-frame or 1.3x crop-factor DSLR's drop in price over the next year or two, it might be that I'll be thanking Sigma for their foresight in selling me something I didn't think I needed. Time will tell.

The bottom line is that in my opinion Popeye is the all-round best ultra-wide-angle solution for 1.6x field-of-view cameras: despite the advantages of the fisheyes, I feel that the ease of framing and no post-exposure loss in quality that the rectilinear projection entails outweigh these. It's also a lens with unique creative possibilities for full-frame work -- definitely the best 12 mm rectilinear SLR lens currently on the market. Also the only one.

Appendix: Cleanup Actions

I've made a small Photoshop action set that cleans up some of the lens's deficiencies wide-open. There are two cleanup actions, one for high-ISO and another for low-ISO. They adjust curves with a radial mask to counter the vignetting and improve contrast around the corners, and apply moderately aggressive sharpening with the same radial mask to counter the corner softening. The difference between the actions is that the high-ISO one uses a higher amount and radius but a high threshold for the unsharp mask (to prevent noise going through the roof), while the low-ISO one uses a lower amount, lower radius, and zero threshold. Low-ISO works for me up to ISO400, high ISO above that. Download and season to taste.

The 12 mm f/4.5 test shot, before and after the cleanup action.

The above 12 mm f/4.5 crop, before and after the cleanup action. There wasn't that much less image data in it than in the f/11 shot after all!