How to get sharp images with Sigma 10-20

Started Dec 20, 2009 | Discussions
dopravopat
dopravopat Senior Member • Posts: 1,180
How to get sharp images with Sigma 10-20

I want to share with you my experience withe the Sigma 10-20mm F4-5.6 EX DC HSM. Owning the lens for almost three years now, it is my favorite and probably mostly used one.

However, I noticed that the sharpness is lower at various parts of the image. I use the lens very long in manual focus mode and keep it at infinity. But the problem with this lens is (at least on my copy) a soft area in the image field, near the sides (see image for details). The problem is more visible on the left side, but appers on the right too. When zooming in, the soft area moves to the edge.

I went through my older photos shot with the Sigma 10-20 and noticed that not all have this softness. I was curious so I made a test. It is not very scientific, but today I finally found the time and the weather was nice and I found a suitable scene. This test is about focus, not aperture.

All images were shot from tripod with mirror lock-up and selftimer. Camera was the Canon EOS 30D, ISO 100, lens zoomed to focal length 10 mm, exposure time 1/125 s, aperture f8, manual focus. I developed the RAWs in ACR 5.0 with the default sharpening.

As we can see, at f8 there is no difference in the central image area (crop 1), but there is a huge difference near the edge (crop 2) and the extreme border is again without any major differences (crop 3). I guess that opening the lens to f5,6 would give similar results. I also added pictures of how the lens was focused. The lens images were taken at home and represent the actual focusing ring positions, which were set when photographing the test scene.

Conclusion: I will use manual focus far behing infinity, the last column in this test, as it gives the best results, without affecting central or extreme border sharpness. I wante to do this test for some time now, as the incosinstent image sharpenss across the field could not be explained other that accidently turning the focusing ring when handling the lens.
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Erik
http://jalbum.net/users/eziak

 dopravopat's gear list:dopravopat's gear list
Canon EOS 30D Canon EOS 60D Canon EF-S 18-135mm F3.5-5.6 IS Sigma 8-16mm F4.5-5.6 DC HSM Sigma 18-35mm F1.8 DC HSM Art +5 more
dopravopat
OP dopravopat Senior Member • Posts: 1,180
Warning! Large files

test scene:

focus and 100% crops:

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Jaysam Thanki Regular Member • Posts: 172
Re: How to get sharp images with Sigma 10-20

I too love this lens, it is sensational. When i first got it, i had a "soft left side issue" which wsa a known issue. Sending it to sigma fixed it, they recalibrated it and now its always good.

Consider sending it to sigma for calibration. Their QC isnt the best.

SpartanWarrior
SpartanWarrior Veteran Member • Posts: 3,015
Re: How to get sharp images with Sigma 10-20

Yes very intresting, I also sent my 10-20 in to sigma service to have them check it out and they told me that it has no problems it is a great lens;)
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300.

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dopravopat
OP dopravopat Senior Member • Posts: 1,180
About servicing my 10-20

I was considering it, but after todays test I doubt they will physically move any elements inside the lens, maybe they would move the focus indicator or do nothing at all. Since I found that by focusing behind infinity I get a very good sharpness across the whole image field, no service is needed.
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Erik
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 dopravopat's gear list:dopravopat's gear list
Canon EOS 30D Canon EOS 60D Canon EF-S 18-135mm F3.5-5.6 IS Sigma 8-16mm F4.5-5.6 DC HSM Sigma 18-35mm F1.8 DC HSM Art +5 more
Phillip Tornero Contributing Member • Posts: 601
Re: How to get sharp images with Sigma 10-20

then why did you send your lens in for servicing? what did you think was wrong with it?

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SpartanWarrior
SpartanWarrior Veteran Member • Posts: 3,015
Re: How to get sharp images with Sigma 10-20

Actually I sent my Sigma 30 1.4 that needed calibration and decided since it was going to Sigma service might as well send the 10-20 just to be sure thats all;)

Phillip Tornero wrote:

then why did you send your lens in for servicing? what did you think was wrong with it?

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300.

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plantdoc Veteran Member • Posts: 3,936
Re: How to get sharp images with Sigma 10-20

My copy shows odd sharpness issues depending on the focal length, distance and F stop. I haven't spent enough time to figure out just when the problem occurs and when it doesn't. It's not like the lens is soft in the corners and then sharpens when stopped down. Most of the problem is along the right side and in a zone on the top. Strangely, indoor shots at 20-60 ft (tripod) are sharp across the frame, but the same focal length and f stop, outdoors with more distance shows the problem. Perhaps, I'll try checking the focus, but at 14mm and f11, the depth of field should easily cover any minor focus errors. I think the problem is more complicated, but who knows.

Greg

plantdoc Veteran Member • Posts: 3,936
Re: How to get sharp images with Sigma 10-20

Interesting test photos. This is somewhat what I see with distance pics. I will definitely try your manual focus beyond infinity to see if this improves a very odd sharpness problem in selected areas depending on focal length. You would think that depth of field at f8 and 10mm would cover everything from 15 ft to infinity..just a guess as I don't have a depth of field calculator any more.

Greg

plantdoc Veteran Member • Posts: 3,936
Re: How to get sharp images with Sigma 10-20

I ran a series of infinity test shots at f8 at a range of focal lengths spanning 10 to 20mm. One series was the focus as found by the camera, and the other I used a focus position just touching the infinity symbol. At 10mm, 12, 14mm, this approach created very sharp pics and eliminated the blur I have often found at the top and right side of image. At 17mm and 20mm, everything was tack sharp except the foreground (shot down from window) about 100 meters away started to go soft with 20mm the worst. Everything else was tack sharp. With camera focus, the closer area was sharper but the rest of frame (esp. right and top) were somewhat soft. Very strange behavior for a well made lens. Far too late for a return and I can't see how it could be fixed. Depth of field doesn't really seem to hold up and it should be substantial for this lens. When I use it for more distant pics (beyond 30-50 ft or so), I will have to use 2 shots...one manual set focus, one camera AF. I really can't judge focus through viewfinder so that won't work. Almost like a 30 year old pocket camera, where you had to guess and set the focus distance. I will try a another series at f11 and closer and infinity distances. I am hoping that at f11, I can just set the focus to near the infinity symbot and forget about it.

Greg

mu55 Senior Member • Posts: 1,407
Re: Warning! Large files

Interesting - I had this lens for a while and loved it - I got a 5D and sold it - replaced with the 12-24mm, I'll have to try the same trick with that - so far I just leave it focused halfway between 2m and infinity, but never done any real tests.
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dopravopat
OP dopravopat Senior Member • Posts: 1,180
How is the 12-24 on FF?

Can you please write me how the 12-24 is on FF, compared to the 10-20 on crop? What differences do you see apart from the wider angle? Any problems? How are the distortions, flare, vignetting, focus compared to the 10-20? Thanks.
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Erik
http://jalbum.net/users/eziak

 dopravopat's gear list:dopravopat's gear list
Canon EOS 30D Canon EOS 60D Canon EF-S 18-135mm F3.5-5.6 IS Sigma 8-16mm F4.5-5.6 DC HSM Sigma 18-35mm F1.8 DC HSM Art +5 more
dopravopat
OP dopravopat Senior Member • Posts: 1,180
Interesting

It seems as if some lens elements were not aligned correctly, both in your lens and mine. But as long as we know how to get sharp images across the whole frame, it does not matter that much. However, relying on DOF with the Sigma 10-20 is not a good idea either. Focus is critical.
--
Erik
http://jalbum.net/users/eziak

 dopravopat's gear list:dopravopat's gear list
Canon EOS 30D Canon EOS 60D Canon EF-S 18-135mm F3.5-5.6 IS Sigma 8-16mm F4.5-5.6 DC HSM Sigma 18-35mm F1.8 DC HSM Art +5 more
plantdoc Veteran Member • Posts: 3,936
Re: Interesting

I would be interested in knowing what would cause such an odd blur situation, but then I am not an optical engineer. However, I have used a variety of lenses for 40 years, and I have seen the typical design limitations, such as soft in the corners, softer wide open, etc and construction flaws, such as soft along one side, but this 10-20 situation is new to me. I thought that a $500 lens with complex optics and construction would be quickly and automatically tested at the factory with lasers, computers, robots, etc. I think the good copy vs bad copy issue has some validity. Just my .02 cents

Greg

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