The old "Sigma focus problems" chestnut...

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bozwellox

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Hi folks,

I took delivery of a shiny new Sigma 24-70 f/2.8 HSM today, and in my initial tests (all at fairly close range) I was very pleased with it, sharp images with accurate focus. However, I took it out to take some shots earlier and it seems like it is not focussing accurately when shooting things further away (about 20-30 feet or so) - to the point that nothing is sharp.

I was sticking to f/2.8 as I was on the lookout for focus problems, and they will clearly show up more using a narrower depth of field.

I haven't done any thorough (read: boring) tests yet, such as the batteries lined up test, due to not having enough light this evening to give it a fair chance.

So, I don't know whether to send it back and get another in the hope the next one works better at all distances, or whether to just send it off to Sigma to have it calibrated to my 5D.

I suppose what I want to know is whether Sigma will be able to fix it so it focusses accurately at all distances, or not. The 5D doesn't have micro-adjust, so I can't play around and see if I can improve on it myself.

Anyone with any experience of this kind of thing, either good or bad, please feel free to chip in!

And before anyone says "sell it and buy a Canon 24-70" - that isn't an option, sadly. The Sigma is £550, the Canon is...well, too much for me.

Thanks peeps! :thumbs:
 
Thanks for the suggestion, but it's quite a bit more expensive and I need f/2.8 as I shoot a lot in low light. So not that helpful really.

To clarify, I'm already astounded that my wife hasn't divorced me for spending £550 on a lens "we" don't need, so any suggestions along the lines of spending more money on an alternative are a non starter.

I bought the Sigma pretty much expecting to have to send it off to have it calibrated to my 5D,but what is confusing me is that it seems fine at closer distances. Is that just because any errors in focus are more obvious when the subject is further away? Or is it possible for a lens to focus more or less accurately at different distances? My head hurts...

So, if anyone has any input on wonky focusing that only seems to rear its head at longer distances I'd be interested to hear your thoughts.
 
The first thing to discount is your own technique so be sure that you are actually focusing on your target and not something in front or behind it and make sure that the target is actually something that the camera has a good chance of locking on to. Do you have DPP? If you do you can also review where your focus point is/was when you took the picture.
 
Yep, checked the focus point in DPP and in my opinion it should have been able to focus properly each time (on my very still daughter's eyes - viewing at 100 percent it's not even remotely sharp).

I will do some tripod/static subject tests before I send it back, but so far my "real world" tests aren't looking good.

Like I say, I'm quite happy to send it in for calibration as hopefully it's just a slight mismatch with my camera, but I'm aware that I only have so long before I can return it to Amazon for a replacement or refund, so I'd like to hear from anyone who has had a similar problem that got it sorted (or not) via calibration.

Thanks for the input! :o)
 
Similar issues with mine on 7d. Front focus on close up shots and back focus on things further away. Need to get it back to sigma for calibration, but until I do I just don't shoot wider then f4.
 
Centre AF point only, don't choose a silly close subject, say 2m min but at the kind of distances you're using, 20-30ft, it will be hard to see any focus error due to the generous depth of field. Focus on a flat target that more than covers the AF point so that there's zero possibility of it picking up on something else. Keep shutter speed well up, use ISO to get it.

If the focus is noticeably out at 20-30ft, that's not just a bit of miscalibration, but a fault. Or camera shake ;)
 
HoppyUK said:
Centre AF point only, don't choose a silly close subject, say 2m min but at the kind of distances you're using, 20-30ft, it will be hard to see any focus error due to the generous depth of field. Focus on a flat target that more than covers the AF point so that there's zero possibility of it picking up on something else. Keep shutter speed well up, use ISO to get it.

If the focus is noticeably out at 20-30ft, that's not just a bit of miscalibration, but a fault. Or camera shake ;)
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Good tips, thanks! I'll take it out later and find something suitably large and flat (a road sign or something) and see what happens. Cheers! :thumbs:
 
If its brand new send sigma an email and they should calibrate it for free.
 
I will probably end up doing that, but want to be sure it is something that can be fixed by calibration, rather than something more serious. Don't want to be lumbered with a duff lens and I've only got 30 days to return it in for a refund.

To make matters worse, the engineer at Sigma who does the calibration is on leave until the end of the month, so they aren't carrying out any calibrations until then!
 
I thought it was not recommended to calibrate zoom lenses, or am I mistaken.
 
Well, I asked this question a while back about my Sigma 150-500. Apparently it's because if they calibrate it at, say, 70mm then it could be out at 24mm.
I'm no expert, just passing on what was suggested.
 
WillyB said:
Well, I asked this question a while back about my Sigma 150-500. Apparently it's because if they calibrate it at, say, 70mm then it could be out at 24mm.
I'm no expert, just passing on what was suggested.
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if that is the case, then there is something really wrong with that lens internally, and in those cases the problem could be too complex even for the service to repair satisfactorily (but they will say it is within spec)
 
WillyB said:
Well, I asked this question a while back about my Sigma 150-500. Apparently it's because if they calibrate it at, say, 70mm then it could be out at 24mm.
I'm no expert, just passing on what was suggested.
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It's true that if a lens is calibrated at one focal length then it can be out at others, but any difference should be very slight.

Even more true is if you use too close a focusing distance for the calibration test, as you are forced to do if you use one of those A4 test targets downloaded from the web (basically, don't) then it may be out at normal shooting distances.

Canon 5D3 allows two calibration settings for each lens, max and min focal length. I've tried that and a couple of my lenses are fractionally different, but the difference is tiny (they're all L-grade which prolly helps) and in practise you'll be lucky if your technique is more accurate than the AF system.

So these things can be a bit of a compromise. Go for the focal length and shooting distance you tend to use most.
 
Remember there is a difference between sending it away to get properly calibrated and using the cameras Micro adjust setting (not aimed at you Hoppy)
 
daugirdas said:
if that is the case, then there is something really wrong with that lens internally, and in those cases the problem could be too complex even for the service to repair satisfactorily (but they will say it is within spec)
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This was not from Sigma but a post on here. I was not having noticeable problems with the lens, just thought it might be worthwhile having it checked.
 
Sigma have got really sloppy with their quality control recently. Their 12-24mm (widest full-frame zoom on the planet and very desirable) is notorious for all the "bad copies" in circulation. Get a decent used Canon 24-70mm f/2.8 and be happy :)

A.
 
An update from today: regardless of the possible front focusing, there is a bigger problem!

Several times today it just refused to auto focus at all, just made a weird noise but it didn't move. Had to manually twist the focus ring from one extreme to the other to get it to work again.

Needless to say, it's going back!

Sadly even used Canon 24-70 2.8s are out of my price range, so looks like I may have to look at a used 24-105,or get one from an overseas seller.
 
bozwellox said:
An update from today: regardless of the possible front focusing, there is a bigger problem!

Several times today it just refused to auto focus at all, just made a weird noise but it didn't move. Had to manually twist the focus ring from one extreme to the other to get it to work again.

Needless to say, it's going back!

Sadly even used Canon 24-70 2.8s are out of my price range, so looks like I may have to look at a used 24-105,or get one from an overseas seller.
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Sigma 24-70 isn't a bad lens at all for the money. Chances of getting two wrong uns on the trot must be very low. Tamron 24-70 is another option, more money but a good lens and has VC.

But if you don't need f/2.8, 24-105L is a fantastic all-rounder with more range and IS of course. I use it for 75% of everything.
 
HoppyUK said:
Sigma 24-70 isn't a bad lens at all for the money. Chances of getting two wrong uns on the trot must be very low. Tamron 24-70 is another option, more money but a good lens and has VC.

But if you don't need f/2.8, 24-105L is a fantastic all-rounder with more range and IS of course. I use it for 75% of everything.
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I totally agree with you, I've seen plenty of evidence that shows how good this lens can be, and I'm actually a big fan of Sigma - my 30mm is amazing on my old 40D, my 50mm is slightly front focusing but is unbelievably sharp wherever it decides the point of focus is (being sent for calibration soon), and my 17-70 is simply amazing on the 40D. I'm going to struggle to find a suitable full frame alternative.

I think I'll try another copy as I really would like the 2.8 option, but the extra reach and reliability of the Canon 24-105 is very tempting.

Thanks for the input squire.
 
Anorakus said:
Sigma have got really sloppy with their quality control recently. Their 12-24mm (widest full-frame zoom on the planet and very desirable) is notorious for all the "bad copies" in circulation. Get a decent used Canon 24-70mm f/2.8 and be happy :)

A.
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The Sigma 12-24 isn't that desirable, it's not great on FF IMO, even good copies have corner softness. Not saying its not good, just not great. Also the Canon 8-15 L is the widest FF zoom ;)
 
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I'm very happy with mine on FF and one good thing is that there's next to zero distortion. Softness? Well, that's up to us each to assess but given the lenses spec and strengths it's deffo worth a look.

I'm very very happy with mine and centre sharpness will shave your beard off! :D
 
woof woof said:
I'm very happy with mine on FF and one good thing is that there's next to zero distortion. Softness? Well, that's up to us each to assess but given the lenses spec and strengths it's deffo worth a look.

I'm very very happy with mine and centre sharpness will shave your beard off! :D
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Don't get me wrong, if I didn't have my 10-22 on my 50d, being a bit of a ultra wide fan I'd be getting the 12-24 for my 5d in a flash! I just can't justify it when I have the 10-22 for the 50d as that combo is soooo good!
 
odd jim said:
Don't get me wrong, if I didn't have my 10-22 on my 50d, being a bit of a ultra wide fan I'd be getting the 12-24 for my 5d in a flash! I just can't justify it when I have the 10-22 for the 50d as that combo is soooo good!
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Just shows how personal experience can vary. I had the Canon and prefer the Siggy as in my experience it has less vignetting, less distortion and more accurate colours although to be fair none of those will probably matter that much as they can all be corrected post capture.

Unfortunately focus errors are another matter :shake:
 
woof woof said:
Just shows how personal experience can vary. I had the Canon and prefer the Siggy as in my experience it has less vignetting, less distortion and more accurate colours although to be fair none of those will probably matter that much as they can all be corrected post capture.

Unfortunately focus errors are another matter :shake:
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moderate distortion, CA and vignetting can be easily fixed. On the other hand, missing blurry details can't be reinvented by software.
 
Distortion? There's hardly any, none really. Look at the review sites and you'll see the distortion is sort of wave like and not like the normal distortion you could expect from UWA. In shots containing straight lines even near the edge of a FF there is no visible distortion but even so even a relatively poor performer like the Canon which will display true and visible distortion will have much less distortion than even a quality standard zoom at its wide setting. It's all relative. Even if distortion or softness is present with any lens at least it'll get you an image and then you can decide if it's good enough or not. Personally for me the 12-24mm is good enough and up to A3 I just don't see the problems others complain of as being issues plus when you want to go as wide as the Siggy your options are rather limited.

On APS-C though the corners are easily up to the APS-C only competition :D
 
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