Sigma 50mm f/1.4 EX DG HSM
Lab Test Results
March 29, 2009
by Andrew Alexander
Fast prime lenses took a back seat to zoom lenses over the past few years - so much so that Sigma was able to identify an unfilled niche and slip in with the 50mm ƒ/1.4 EX DG HSM. Using a design that departs from convention, the lens is much larger and heavier than its contemporaries, weighing in at 505 grams (just over a pound) and requiring 77mm filters.
The Sigma 50mm ƒ/1.4 was designed to accommodate the 35mm film frame, and is available for all SLR camera mounts: Canon, Nikon, Sony/Minolta, Pentax and Four-Thirds. On Canon sub-frame sensor bodies the lens provides an effective field of view of 80mm; on Nikon the field of view is effectively 75mm; and on Four-Thirds subframe bodies, the field of view is effectively 100mm.
The Sigma 50mm ƒ/1.4 is available now for a street price of under $500.
For the most part, the Sigma 50mm ƒ/1.4 is a sharp lens. However, there are some very notable exceptions. Let's take a closer look.
On the sub-frame Canon 20D, when shot wide open at ƒ/1.4 the lens produces images that are just slightly soft - between 2 and 3 blur units across the frame. Stopped down to ƒ/2 and sharpness improves dramatically, now showing results between 1 and 2 blur units, and further improvement shows at ƒ/2.8. Image sharpness peaks at ƒ/4 and stays there until ƒ/11, where we see numbers that still stay below 2 blur units. At ƒ/16 we still note very good performance, with an average performance of around 2 blur units.
|Canon 5D, ƒ/1.4|
With the lens mounted on the 20D, the sensor is focusing on the ''sweet spot'' of the lens, and corner softness really isn't a substantial issue. Mounted on the full-frame 5D and shot wide open at ƒ/1.4, the 50mm ƒ/1.4 shows extreme (off the charts) corner softness. It's worth noting that this corner softness is limited to the exterior 25% of the image - that is to say, it really only shows up when used on a full-frame camera.
Corner softness is significantly reduced as the lens is stopped down, but it isn't until ƒ/5.6 that corner softness falls below 2 blur units. From ƒ/2.8 on, central sharpness is very good, on the order of 1 blur unit, and by ƒ/5.6 the lens has reached its optimum setting; excellent central sharpness with corners that are negligibly softer. Diffraction limiting begins to set in at ƒ/8, but image sharpness is only slightly affected. Even at ƒ/16, we note only 2 blur units across the frame.
In short, excellent results on a subframe body when stopped down to ƒ/2.8, and slightly soft when used wider than that. On a full-frame body, you have to contend with some corner softness until ƒ/5.6.
The Sigma 50mm ƒ/1.4 controls chromatic aberration very well, with the maximum recorded CA (in the corners) registering at just 3/100ths of a percent of frame height (on both the 20D and 5D).
Corner shading isn't much of an issue on the sub-frame 20D; when used wide open at ƒ/1.4, the corners are almost a half-stop darker than the center. Stop the lens down to ƒ/2 or smaller, and light falloff drops to a quarter-stop and stays there throughout its aperture range.
With the lens mounted on the full-frame 5D, corner shading becomes a bit more apparent. When used wide open at ƒ/1.4, the corners of the image are 1 1/4 EV darker than the center. Stopping down reduces the light falloff, with differentials of over 3/4EV and 2/3EV at ƒ/2 and ƒ/2.8 respectively; it isn't until ƒ/4 that the corner shading levels off at a consistent half-stop.
The 50mm ƒ/1.4 is optimized nicely against distortion, showing just +0.25% barrel distortion in the corners when mounted on the sub-frame 20D. When mounted on the full-frame 5D, this distortion is slightly more pronounced, with a maximum of +0.4% barrel distortion in the corners.
The Sigma 50mm ƒ/1.4 uses Sigma's HSM (Hypersonic Motor) focusing technology, producing fast and near-silent autofocus results. It takes about a second to focus between infinity, close-focus, and back to infinity. The focus ring doesn't move during focusing, and autofocus results can be overridden at any time by simply turning the focus ring.
The Sigma 50mm ƒ/1.4 isn't designed as a macro lens, providing just 0.14x magnification, and a minimum close-focusing distance of 45cm (around 1 1/2 feet).
Build Quality and Handling
The lens is made of a solid and durable plastic, with a matte off-black finish. There is no rattling or flexing to be found with this lens. Its solid weight (505g, just over a pound) makes it balance quite easily on larger cameras, though on smaller bodies such as a Nikon D60 it could be slightly front-heavy. The lens uses a metal mount and plastic filter threads. There is no aperture ring.
The 50mm ƒ/1.4 offers a few distinguishing control features, including a focus override switch as well as a recessed and windowed distance scale. The scale shows distances in feet and meters, with a depth-of-field reference scale for ƒ/8 and ƒ/16. There isn't a lot of detail on the scale however, so its usefulness could be questionable. There's also no infrared index.
The focus ring is about a half-inch wide, using a rubber texture with lines running parallel to the lens body. The ring takes about a quarter-turn (~90 degrees) to move through its focusing distance; the ring is slightly stiffer than usual, but still turns easily through its range. An increase in resistance alerts you that you have reached the end of the focusing range. You can still keep turning the ring, however. The lens will focus a bit past infinity. The front element does move during focus operations, but doesn't extend past the front of the lens; attached filters will also stay put during focusing, making polarizers that much easier to work with.
Sigma includes a lens hood with the 50mm ƒ/1.4, a petal-shaped, bayonet-mounted hood that adds an additional 1 3/8 inches to the overall length of the lens. The hood is ribbed on the interior, and will reverse and mount on the lens for easy storage.
While Sony and Olympus both offer 50mm lenses, I'm not including them in the list of alternatives. In the case of the Sony because we have not yet tested it, and in the case of the Olympus, because it is a 50mm ƒ/2 macro lens, which (while an excellent lens) isn't really in the same category as the Sigma 50mm ƒ/1.4.
Canon EF 50mm ƒ/1.2L USM ~$1,400
The Canon 50mm ƒ/1.2 offers slightly better results for sharpness, especially on full-frame; by ƒ/2.8, the Canon ƒ/1.2 is very sharp. However, it's also almost three times the price. CA performance is almost the same, perhaps slightly better for the Sigma. Distortion and corner shading results are about the same between both lenses.
Canon also produces the 50mm ƒ/1.4, but the Sigma is significantly sharper at ƒ/1.4. That said, stopped down to ƒ/2.8, the Canon ƒ/1.4 produced slightly sharper results and achieved tack-sharpness by ƒ/4. CA is also very good, better even than the Canon ƒ/1.2; corner shading and distortion results are similar.
Nikon 50mm ƒ/1.4G AF-S ~$475
The Nikon 50mm ƒ/1.4 is softer at ƒ/1.4, but stopped down to ƒ/2.8 and smaller begins to edge out the Sigma for overall image sharpness. It isn't marred by the obvious corner softness of the Sigma. Corner shading and distortion are similar between both lenses, with the Nikon showing perhaps slightly more distortion. On the D200, CA performance is similar, perhaps just slightly worse than the Sigma; on the D3X, there's virtually no CA to speak of.
Nikon also produces the 50mm ƒ/1.4 AF-D, which does not focus on D40/D40x/D60 bodies, but offers improved sharpness at ƒ/1.4. We haven't yet tested the lens on a full-frame body, but image sharpness, CA performance, corner shading and distortion show similar results between both lenses.
Pentax 55mm ƒ/1.4 SDM SMC DA* ~$700
Pentax's comparable lens is the 55mm ƒ/1.4. At around $700 it's the most expensive lens in its category, but offers the best results of them all. It's decently sharp wide open at ƒ/1.4, and by ƒ/2.8, it's about as sharp as we can record. CA performance is good wide open, slightly worse as the lens is stopped down. Corner shading and distortion are both slightly better than the Sigma. Did we mention it costs $700?
Pentax does produce an older 50mm ƒ/1.4 SMC PF-A, but we haven't yet had the opportunity to test it.
Carl Zeiss 50mm ƒ/1.4 Planar T* ~$500
If you're okay with sacrificing autofocus, Carl Zeiss offers a 50mm ƒ/1.4 in Nikon, Pentax, M42 and Canon body mounts. The lens performs extremely well when stopped down to ƒ/2.8; at ƒ/2 it shows significant corner softness, and results are generally soft when used wide open. CA is fairly high in comparison to the Sigma; corner shading and distortion are around the same.
The Sigma 50mm ƒ/1.4 is an interesting lens, offering excellent resistance to chromatic aberration and low distortion. Corner shading isn't an issue when used on a sub-frame body, but on a full-frame body it's significant, and distinctive in that it never really goes away. The best you can get is a situation where the corners are a half-stop darker than the center, which I suppose isn't the end of the world, and is fairly easy to correct in post. It also serves to isolate a centrally-located subject from its environment. In the same vein, extreme corner softness can have the same effect, which is the case when used wide open on a full-frame body; the results aren't nearly as dramatic on a sub-frame body. Stopped down to ƒ/4 or ƒ/5.6, the lens offers fairly uniform and excellent sharpness.
So is the Sigma 50mm ƒ/1.4 the lens for you? In comparison to some of its contemporaries, it offers slightly better wide-open performance; for many people, this will be the deciding factor. If you're not shooting the majority of your 50mm shots at ƒ/1.4, then there are many more options; otherwise, the Sigma 50mm ƒ/1.4 could be an excellent addition to your bag.
The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.
As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.
Sigma 50mm f/1.4 EX DG HSM
Sigma 50mm f/1.4 EX DG HSM User Reviews
8 out of 10 points and recommended by KTR (3 reviews)Wide aperture Fast focussing Solid build Excellent IQ overall Versatile Pleasant to useCorners are not so sharp as some alternatives Quite big and heavy compared to alternatives No Image Stabilisation Not weather sealed
This is not a lens I would have considered except that I was offered it at such a bargain price that I could not refuse. I have been nicely surprised. I find that having more flexibility in aperture makes a prime lens like this more useful than a mid-range zoom such as the 24-70 f/4 that it has replaced in my bag.reviewed September 6th, 2017
The corner sharpness that all the on-line reviews mention, and that some consider to be a terrible flaw is actually irrelevant to the way I use the lens. When I am shooting at a wide aperture it is usually because I want to set a sharp subject against a blur of colour. The background is out of focus anyway so the lack of corner sharpness is irrelevant. When I am shooting a landscape or townscape or interior, and want great depth of field I would be stopped down to f/5.6, f/8, or even narrower, and at those apertures the difference between centre and corner is not significant.
Another thing the lens has been criticised for is the filter size. For me it is no disadvantage. It can share 77mm filters with my Canon 16-35.
Finally a big deal is made of green and purple fringing in front of and behind the focus point. This is so easily corrected in LightRoom (one or two points in Lens Corrections, Colour, Defringe) that it is hardly worth a mention.
10 out of 10 points and recommended by JimG (1 reviews)Very sharp, Excellent IQ, Fast to focus, Solid buildLow light focus sometimes off
I have read all the issues users have had with inconsistent focus on this lens. These reviews were from 2007~2013. It is now mid 2015 and I have not had any focus issues at all with this lens. Focus is fast and dead on. I am guessing Sigma corrected the focus issue or I got lucky. Excellent contrast and colors. Lens is heavy and solid. The massive 77mm front lens does pull in a lot of light but 77mm make filters a little expensive. Supplied hood is thick, solid and mounts securely. All in all, I am happy with this lens and got it during Sigmas $100 off sale but would have been worth $500. If I had to pick a gripe it would be the lens is slightly soft at 1.4, but this is to be expected, but much better than the Nikon 1.4 also low light focus can sometimes be off, it can not focus on what it can not see but neither can I so I can not complain. This lens stays on my camera all the time.reviewed June 26th, 2015 (purchased for $400)
9 out of 10 points and recommended by titi_elsass (7 reviews)Well builted & shape, enough sharp at f/1.4, colors, contrast, bokehAutofocus non consistent
Having bought this lens one year ago, I'm still impressed by the image quality. It's the non-ART version but with "silk" finish. It's really a good mix of sharpness and nice bokeh (out-of-focus areas, very smooth). My copy delivers enough sharp images at f/1.4, and at f/1.8 very sharp ones.reviewed June 24th, 2014 (purchased for $300)
I really like the build quality (even the hood is nice) and the shape of the lens: short but wide.
The downside of this lens is the Autofocus: it's enough silent, fast but not really consistent. You should consider this lens like a manual lens with an autofocus in bonus, but you can't rely on it. You need to focus by live-view (Magic Lantern helps a lot!) or through the viewfinder coupled with a precise matte glass like Ee-S or Eg-s on 5D series.
8 out of 10 points and recommended by TomE (4 reviews)sharp at close distanceuseless wide open beyond 3 meters
I use this lens for portraits on a Nikon dx. Ultra sharp, even wide open (only if I shoot head shots). Wonderfull bokeh also. The only problem I have with this lens, is that for all other use, it just doens't focus correctly. Most of the time it backfocusses. I tried it on several body's, but it's just not good. So it's not a walk around lens, or if you are looking for a lens to shoot concerts etc, forget this lens.reviewed May 30th, 2013 (purchased for $450)
8 out of 10 points and recommended by Yucel (15 reviews)Great Bokeh, Very Sharp, 77mm Pro FiltersLarge Green Ghost images from highlights wide open, sometimes
An beauty glamour headshot image taken with this lens @ f9.0 in studio with a Nikon D90 along with some brief details are avail for view here: http://glamourphotography.co/?p=6588reviewed April 16th, 2012
Some may say f9.0 is not a fair test of a fast portrait lens.... I say, on a D90 crop sensor camera, a 50mm is an excellent portrait lens, and in studio, using studio lights, most shots are taken at f5.6 to f9.0.
If you like to see the image larger, view here: http://www.yucelphoto.com/Glamour-Beauty-Boudoir/Beauty/13795570_wqDTM8#!i=1794846338&k=RxczQ4v&lb=1&s=X3
This is not a bokeh shot... It's a shot showing use in beauty portraiture stopped down to where the lens is sharpest.
10 out of 10 points and recommended by Suntoro Tjoe (3 reviews)Very fast AF, great bokeh and impressively sharpFilter size
I have been using this lense for almost a year on mostly portrait photography. The result is impressive, both sharpness and bokeh. It is one of the best lense in the class.reviewed August 11th, 2011 (purchased for $420)
I feel the size and weight are just perfect on my D300 with vertical grip.
Highly recommended for portrait photography.
For sample images www.ourphotolib.com/suntoro/g15/
10 out of 10 points and recommended by MS (2 reviews)Excellent IQ
I'll give it a 10 because I got a very recent copy and it does not have any meaningful focus shift and the autofocus is working well even in low light. The bokeh is great, color is very good though Canon L sometimes, but not always, beats it. Overal IQ is very, very good. Excellent build quality.reviewed May 6th, 2011
8 out of 10 points and recommended by kaci (10 reviews)super sharpAF accuracy, atmosphere, bulky, price, f1.4-f1.6
I owned this lens for two months, then sold it and kept my little gem Canon EF 50/1.8 II. My Sigma was super sharp above f1.8. But at f1.4 - f1.6 was unuseably soft. The AF was quick, but front-focused a lot which was a problem. I didnť like the general output from this lens a lot = it looked liked a entire copy of a reality without any atmosphere which my Canon primes have and I love. And it is also really bulky and heavy compared to other 50mm primes.reviewed April 15th, 2011 (purchased for $470)
I would recommend it for general purposes but for dreamy portraits definetely not.
10 out of 10 points and recommended by sebkaine (1 reviews)very sharp + great bokeh + very affordablefocus on low light
This lens is one of my favorite. It just take wonderful shots. it is sharp at f1.4 compared to the canon 50 1.4.reviewed January 28th, 2011 (purchased for $500)
The lens has a very good construction quality, but it's not L. the only cons is that it is quite big and in certain condition the focus is lousy in extreme low light scene.
you won't regret this lens.
9 out of 10 points and recommended by Beachrider (22 reviews)Wonderful function at f/2.2, usable down to f/1.6, HSM is niceHeavy and expensive
Special lens with above average color rendition. Images at f/1.4 were soft on APC-size, but quite usable after that.reviewed December 29th, 2010 (purchased for $500)
This allows the use of natural light in many scenarios, especially where high-ISO digital SLRs are being used.
I like this lens
3 out of 10 points and not recommended by uforias (3 reviews)Good OpticsInconsistent Auto Focus
Unfortunately another disapointment with Sigma Quality Control. They have ruined an optical excellent product due to inconsistent Auto Focus. At least with Canon gear, you better stay away from Sigma Lens. I have to compensate from -5 micro adjustment for up 1 meter distance to almost +20 on the worst scenario for longer distances. Furthermore, even microadjusted the keeper rates are below 25% because the AF isn't consistent.reviewed October 24th, 2010 (purchased for $600)
9 out of 10 points and recommended by DoFJerk (7 reviews)Sharp, Impressive Axial CA, Low vignette, Good BokehAF in low light, bulky, soft at corner
I use this lens with D700.reviewed July 16th, 2010 (purchased for $420)
This lens make me happy when shot at large aperture, the Axial CA is lower than other lens in the same class.
The Bokeh is also very nice. Very sharp event at f/2.0.
Found some AF hunting under low light, but not much a problem.
9 out of 10 points and recommended by Eager (7 reviews)fast, sharp, great bokehbig&heavy, 77mm filter size
Realy great portrait lens for a crop sensor. My copy is sharp over all frame even wide open; fast and true autofocus operation; good color and creamy "impressionist" bokeh. Ah! Just wish it to be not so bulky and heavy!reviewed June 23rd, 2010 (purchased for $500)
10 out of 10 points and recommended by xxcromxx (1 reviews)the bokeh, IQ, HSM, color, contrast, hoodnone
This is my most used lens. Very sharp, usable at 1.4 amazing at 2.0. The bokeh is creamy. I'm just happy with this lens.reviewed June 8th, 2010 (purchased for $488)
10 out of 10 points and recommended by nthomas (1 reviews)Nice IQ, Perfect DOF, nice warranty service, great colorSome QC problem, may encounter product issue.A little bit too heavy.
This is my favorite portrait lens. I would say this is the best 50mm you must have. It is ever superior than the Canon 50L with only one third of the price.reviewed May 28th, 2010 (purchased for $470)
9 out of 10 points and recommended by Lardinio (2 reviews)Right balance on D300, quick & quiet AF, centre sharpness wide open, bokeh - oh the bokeh!more expensive than nikkor rivals, focus accurancy
Bought it used for £240 in the UK in mid 2009. It's large for a nifty fifty, but feels great on my D300. Sublime bokeh, put my old nikkor 50/1.8 to shame (and so it should!). It's great at 1.4, in the centre at least. Corners are never really that 'sharp' at any aperture, but I wanted it for portraits and candids and it does the job superbly. Can misfocus every now and then (very seldomly) but never a problem for what I wanted it for. Highly recommended.reviewed March 19th, 2010 (purchased for $400)
9 out of 10 points and recommended by RJNaylor (4 reviews)Great DOF controlA little slow to focus in low light
When I first opened the box, (january 22, 2010) it was evening and dark out. I tried some low light shots on objects around the kitchen and was very unhappy with the sharpness; especially compared to my Nikon 35mm 1.8. But, when i sued the flash, it was right on. Also, odd enough a few days later, shooting our cat, I was able to use manual and get plenty of brightness sans flash. So, after worrying that it did not focus properly, I have the immpression it needed to be broken in -- I can't explain it otherwise. Or, perhaps I was nervous the first night. Now I am a happy camper because I love the bokeh and that is why I chose it over the Nikon -- plus it tested sharper wide open on several web sites. I have my Nikon 16-85 for more dof and great sharpness. My 35 1.8 is also wonderfully sharp.reviewed February 8th, 2010 (purchased for $500)
9 out of 10 points and recommended by NLxAROSA (2 reviews)IQ, f/1.4, Bokeh, HSMNone so far
Recently acquired this lens because I do a lot of low available-light action stuff. IQ is excellent, f/1.4 makes sure you can use this baby in the worst light conditions. The HSM AF is fast and quiet. I am using this lens on a subframe camera (EOS 450D) and I have no issues with front- or backfocusing (I specifically tested for it because I read this in the reviews). It's built like a tank too. :)reviewed January 1st, 2010 (purchased for $500)
8 out of 10 points and recommended by MrAdventure (6 reviews)Solid Build, Sharper than Canon's 50 1.4 wide open, good color and contrast...and fastSlight focusing issues, heavier than Canon's equivalent, large filter size
I used it extensively over the past year and it rocks. The Canon is much better in corner sharpness from f/2.8 onwards.reviewed October 7th, 2009
Excellent for low light and natural light work.
10 out of 10 points and recommended by DH (3 reviews)Super!Non
Just one word. Super!reviewed September 25th, 2009 (purchased for $540)
10 out of 10 points and recommended by kevindar (2 reviews)Excellent Color, contrast, build, wide open performance, vignetting, CA controlFocusing a little nervous. May be prone to front focusing
I find the findings of slr test surprising. My copy has very good corner sharpness, even wide open, and thats consistent with findings of DP review. I had to send mine in for front focusing, and even after it came back, I had to make a micro focus adjustment of 8. If your camera has microfocus adjustment then not much of a problem. I would say the focus at times is a little more nervous than canon 50 1.4. The Canon alternative that I had was excellent, but if you shoot under f2, the color, contrast, bokeh, and sharpness of the sigma is noticably better.reviewed September 24th, 2009 (purchased for $500)
I am shooting this lens on a Canon 5D mark II.
9 out of 10 points and recommended by corbeau (1 reviews)image quality: sharp even at 1,4, no disturbing vignette nor fringingbulky, price
When I first got this lens, it showed a marked backfocus. The lens was replaced by the retailer, the second lens was even worse. I sent it to Sigma who adjusted the lens and now it workes fine with my Sony Alpha 700. It really is a great lens.reviewed June 15th, 2009 (purchased for $612)
10 out of 10 points and recommended by RadiantLite (16 reviews)sharp wide open, fast focusingbulky
One of the best 50mm lens ever made. Image quality is very good and sharp even at wide open f/1.4. The AF performs very fast and accurate. Great for indoor sport and low light condition. Highly recommended.reviewed June 13th, 2009 (purchased for $575)
for sample photos and more reviews
9 out of 10 points and recommended by bennike (2 reviews)Picture & Build QualityNone so far
This lense is extremely robust and a pleasant companion to most photographich journeys for an amateur like me. I haven't experienced any downsides yet, other that a little softness on 1.4 aperture. However that was expected...reviewed May 14th, 2009 (purchased for $550)
10 out of 10 points and recommended by Canon-Nikon-user (14 reviews)shapest 50 for sure, no-CA I can see, very fast aF on my 50D and D300.no-canon-or-nikon-so-cheap-resell-value.
this repalced my EF50f1.4USM and Nikon aF-S50f1.4G.reviewed February 22nd, 2009 (purchased for $430)
much sharper than these 2 and much faster aF than both Cand N.
So get it if you have Nikon D700, EOS5D2, EOS50D or Nikon D300, but not get it if you have a D90 or D80 cause I tried it on my D90 (returned) and was not good on it cause slow AF and horrible metering of the D90, it is outstandingly sharp on my d300 with its 51 AF though.
Sigma rocks for now.
update: I forgot to mention this , the Sigma was sharper than the 50f1.2L too.
9 out of 10 points and recommended by maho (1 reviews)works well wide openweight
A very good new prime lens by Sigma. Works well even wide open, which is something new in this aperture 50mm lenses. I use it mostly with Canon 5D and 40D. Can be compared with Canon 35 f1.4 lens, which I also use a lot. In comparison of wide open shots (f1.4) Canon is better but otherwise almost equal.reviewed September 26th, 2008 (purchased for $490)
3 out of 10 points and not recommended by thrice (1 reviews)Great Sharpness and Contrast wide-open, 77mm filter thread for professional filters, great build quality, VERY smoothe bokehThe two copies I've tested have issues with my 5D (and other FF Canon cameras) when focusing beyond 10'
The issue with this lens, on both of the copies I've tested (and every independent individual who I've spoken to shooting this lens on full frame) is that it SEVERELY back focuses when you focus beyond 10' (3m). Granted I only occasionally use the lens beyond that range, but I should be able to without issue.reviewed July 26th, 2008 (purchased for $499)
It's really odd because the image is in focus in the viewfinder (I have split prism manual focus screen) and no matter how many times I refocus it back focuses by about 30-50cm at 3m.
When I focus any closer it is accurate and the image quality is stellar.
I've spoken to Sigma who were less than helpful (even condescending) but the distributor here in Perth (Western Australia) is being really helpful even though I imported the lens. My 5D has been checked and I have many large aperture lenses that have no issues with perfect autofocus at all ranges.
I have tested the lens on an EOS 40D and it doesn't seem to have any issues of note, so for those who never plan to go full frame this is a great lens I wouldn't hesitate to buy.
Given that it is an EX DG lens from Sigma and should work properly on a full-frame body I cannot recommend this lens to anyone using a full frame body and from a resale or upgrade perspective buying one at this stage in time makes little or no sense for any user.