Incense

by Bart Arondson

submit your photo


Hall of Fame
View past winners from this year

Please participate in Meta
and help us grow.

Take the 2-minute tour ×
Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It's 100% free, no registration required.

I recently purchased a Sigma 24-70mm f2.8 lens which I am using on a Canon 40D body. Around 8 of 10 shots were soft, regardless of subject matter. Exposure, white balance etc. all looks fine. I only shoot in manual mode. After doing some research and a professional friend taking some pics (also soft) I took the lens and camera body in and had a firmware upgrade.

Since the upgrade I have seen a huge improvement, however, when it comes to portraiture many of my shots still look soft. This is hampering me enormously as I am trying to go pro, but cannot put my name out with this "track record". I have noticed that distance from subject makes somewhat of a difference (further away = softer). Low light is also problematic despite using a flash. Another friend says Sigma lenses are apparently known to have this "soft" problem. What should I do?

share|improve this question
2  
Hi Geni. Welcome to Stack Exchange! Can you post a few sample images? Ideally, both scaled-down full views and some pixel-for-pixel crops as well. And some background questions: does the behavior change at different apertures? Do the images appear soft or do you mean unsharp in some other way? –  mattdm Nov 2 '11 at 12:05
3  
Could you please post a soft picture with the EXIF information? –  Vivek Nov 2 '11 at 12:53
1  
Check the aperture of the soft images. Just because you lens can do F/2.8, it does not mean it is usable. I found that with a number of Sigma lenses (did have that one though) and would only use them at F/4 or smaller, meaning I only ever could use A, M or TAv modes. –  Itai Nov 2 '11 at 13:27
    
@Itai: This lens can give a decent output at f2.8 the problem seems to be with autofocus as the copies I had could both give decent output when manually focused wide open but auto-focus was all over the place. –  Paul Round Nov 2 '11 at 14:42
    
Thanks for the feedback! My portrait shots were shot at 1/125 ISO125 at f5.6 using a Canon 530EX flash in studio. I did a lot of experimenting yesterday and shots seem really sharp at f4 with the same ISO and shutter speed, although some are not in focus where I set the focus point (on eyes), pics sharp to the right of where I focused (using centre weighted focusing). I'll run more tests tomorrow again and try manual focus. Thank you all very much! –  Geni Nov 2 '11 at 16:04

4 Answers 4

I had the Sigma 24-70 f/2.8 HSM and had all kinds of problems focusing with it. I tried to use it on a Canon 7D and 5D mk II but found much the same problems existed on both bodies. I had problems similar to yours in that there was an inconsistent focal error over the zoom range such that if I corrected for 24 (I don't think you can do this on the 40D) it would give soft focus above 40 and if the subject distance changed this also threw things out. In the end I sent it back and got another copy which unfortunately had much the same problem. After getting the second copy looked at by Sigma the problem was slightly reduced but still not completely resolved.

It's not that the lens cannot focus because I could get pin sharp focus in manual mode but I think it may be a general problem with this lens and autofocus as I have seen lots of forum posts describing similar experiences. In the end I got the supplier to agree that the lens was defective and got a refund. Ended up stumping up the extra cash for a Canon 24-70 f2.8 L which auto-focused perfectly and gave noticeably better image quality but at a pretty hefty extra price.

share|improve this answer

Sigma lenses are known to have this issue on many of its lenses regardless of the type. It's always best to try out the lens first before buying any Sigma.

As of now, the way forward for you would be to try and get a replacement if it's under warranty. Else theres always the hard way - post processing.

share|improve this answer
    
Thank you, I was afraid of this after all the negative reviews I've read. I guess I need to sell and replace. –  Geni Nov 2 '11 at 20:14

I would send it back to Sigma for adjustment, or get a new copy.

Also you could try shooting a focus chart, or something flat to see if focus was de-centered - it could be that things in one side of the frame are more focused than others. Whatever you can document may help Sigma fix the issue your lens is having.

share|improve this answer

I had this lens on my D90 and it was very poor wide open. Sharp at f/5.6, very good at f/4, but horribly soft at f/2.8 - really unusable. I did extensive testing of the lens on a tripod with a test pattern, mirror lock up, manual and AF. It was very soft at f/2.8.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.