Odd problem with AF using a sigma 150mm macro on a Canon 80D

[ajohnw]

I've set the camera up for agile continuous af using the back button option so that the camera continues to focus when ever the button is pressed even when distances are changed. Initially I had the delay change set - the one for if some one walks across the frame etc.

Often something curious happens. I can point the camera at various objects and it focuses but from time to time just locks up and wont focus at all even though it's obviously somewhat out via the viewfinder. If I correct manually it may even still continue to refuse to confirm focus. On odd occasions it will then confirm focus and may shift the focus a touch as well.

I'm using the lens with Sigma's 1.4x converter. Removing that doesn't seem to make any difference.

It's a brand new lens bought in April for this years insects - not that there have been many for me in the UK. Initially I used it on a well used 100D and did notice one problem. If I selected one AF point and went back to more the camera just wouldn't focus at all. Switch to live view and back to the viewfinder and all was ok. The camera wasn't keen on just using one focus point. I have the impression that the 80D isn't either with this lens but have done most testing with a central group of points.

As a check, the only one I can do, I fitted Canon's first ever 70-300mm with IS and set it to 210mm. No problems even in living room level lighting. That's where I have mostly played with the sigma lens - a row of birthday cards around 6ft long. I'm about 10ft from one end. Often the problem crops up when I move to the last one which needs a focus shift of a few inches. It's also happens scanning flowers in a bunch outside in the garden. Out there it generally snaps into focus providing there is a significant change in distance. indoors it may lock up under similar changes.

Any ideas?

John
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[DanK]

I have encountered symptoms similar to this with my equipment if I have the focus range restriction set to the wrong distance. Does this lens have a focus limiting switch, and if so, did you check to see whether you had it set in the right range for the objects on which it wouldn't focus?

[ajohnw]

I tried all of the ranges but not the low distance one as Sigma state that it wont focus below 0.53m with the converter on so the range I have used starts at that and goes to infinity. Just checking though when I tried it outside it was on full so I'll repeat the tests inside the house just in case I have messed up. I'm pretty sure I haven't and did use the correct range. The distance where this has happened are way over 0.53m anyway.

John
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[ajohnw]

No same thing happens. Wont respond to small distance changes. I also tried using the manual focus and shifting it well off. It didn't like that at all and took 3 back button presses to get it to focus again. It just rocketed through the focus point on 2 and then did it correctly. It supposed to hunt for ever.

If I focus on something at circa twice the distance to the card that wouldn't focus and then go back to it it does. The problem only crops up when it needs to change focus distance by inches where it's clearly not in focus via the viewfinder.

I just tried 2 test shots with flash. One where I had slight doubts about it being in focus via the veiwfinder but the focus was shown as ok after slight distance changes. Clearly not well focused on the actual shot. Then I tried a much larger refocus distance change that it snapped to - the shot is pin sharp. Different card to the other one but ...........................

At F13 by the way.

John
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[george013]

No same thing happens. Wont respond to small distance changes. I also tried using the manual focus and shifting it well off. It didn't like that at all and took 3 back button presses to get it to focus again. It just rocketed through the focus point on 2 and then did it correctly. It supposed to hunt for ever.

If I focus on something at circa twice the distance to the card that wouldn't focus and then go back to it it does. The problem only crops up when it needs to change focus distance by inches where it's clearly not in focus via the viewfinder.

I just tried 2 test shots with flash. One where I had slight doubts about it being in focus via the veiwfinder but the focus was shown as ok after slight distance changes. Clearly not well focused on the actual shot. Then I tried a much larger refocus distance change that it snapped to - the shot is pin sharp. Different card to the other one but ...........................

John
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If you're still trying with the converter, take it off.

George

[ajohnw]

Bit of light relief - when it does focus. Not much time to take a shot as it scooted. It's a 50% reduction of a full res crop. JPG minimal processing.



I'll try the converter off - again but don't expect any differences.

John
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[george013]

You've a problem. When yo want to solve that, start focusing on one thing only, the lens. It's ridiculous to examine both.

George

[Geoff F]

I have the 180 Sigma macro lens and find the AF to be unpredictable; slow and hunts a lot before settling on a spot, even then it changes focus from time to time when at close distances. OK for longer shots.

It never bothers me because I always use manual focus when working close and I can actually manually focus at a closer distance than with AF.

Incidentally, I did initially get an occasional fault with the lens when pointing downwards. It wouldn't focus either manually or with auto and the focusing ring just went round and round with nothing happening. Worked fine when pointing upwards. OK after returning to Sigma for a repair.

[ajohnw]

I did mention in the first post I made that removing the converter didn't seem to make any difference.

Just tried again and it doesn't. I also tried a test shot where following a small distance change the camera said still in focus. The shot is most definitely is out of focus. This time I used F8 rather than F13.


John
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[DanK]

I assume your lens is wide open while focusing, so the aperture setting shouldn't matter.

[ajohnw]

I assume your lens is wide open while focusing, so the aperture setting shouldn't matter.

Yes. I used F8 rather than F13 for taking a test shot when the camera was still indicating that it was in focus after a small distance change. The F13 shot shot taken the same way was out of focus and the F8 one worse due to the faster aperture. When I took a shot after it had focused cleanly without this messing about the shot was pin sharp.

I think I will get my hands on the D100 again and try the same sort of thing with that. I may be able to get my hands on the latest 7D as well.

The fact that the camera will indicate in focus when it's not makes me think that end is the problem. Why is a mystery though as it doesn't seem to have any problems with what might be called an ancient L IS 75-300mm. The lens dates back to when Canon bought out the 300D and the digital lenses they introduced with it were crap and only suitable for very low pixel counts. Some how I knew that pixel counts would go up so bought the higher quality lenses to go with the 300D.

John
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[ajohnw]

The 100D worked for one scan of the cards but not all and there was some signs of miss focusing when a shot was taken after a large distance change. That could be down to the limited AF capabilities and light levels.

So this sort of suggests lens or Canon not bothering to work with it 'cause it's not a Canon lens.

I then tried it on a 5D III. Same problem except as I reframed it did warn me about out of focus but if I released the focus and activated it again it wouldn't focus cleanly. Not sure on setting here but selected A1-Servo. I'd have to read the manual to see if that had hidden features but releasing focus and setting it again should do what it says on the can. I also waited more than long enough for the "problem" being some one walking across the frame. It's my son's camera. He uses it in auto and bought it specifically for a month holiday in the USA. I must admit having seen a lot of the shots full size that it looks like auto is way way more clever than others. He wondered about softness in some images but it was mist/murk and slight signs if shake in some that looked like a shutter button pressing problem.

John
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[DanK]

It seems to me that you have shown that the problem has to be the lens, since it happens on several different camera bodies.

I'm not sure what you mean by 'he uses it in auto'--I don't know which auto mode you mean--but the AF in the 5DIII (my main camera) is superb. If by auto, you mean AI-servo, then I don't agree. In single shot mode, the AF is excellent. I use 4 different lenses with my 5DIII (all Canon, unfortunately for your purposes), usually in single-shot mode, and all focus very well.

[ajohnw]

Sorry Dan - I meant that he uses the camera in the auto setting. Nothing to do with AF. He will have been using what ever AF mode that chooses to use. All setting at default as well. I was just surprised given the number of shots he took that the camera coped pretty well with all of them.

I've spoken to the people that sold the lens to me and they have suggested back to Sigma. There are some comments about on the web concerning this lens focusing - or not. I suspect this is exactly what I have noticed. I was choosing a flower in a bunch in the garden to shoot and noticed that as I switched flowers it wasn't focusing as I panned the camera over them. If some one didn't notice the same problem could crop up shooting insects. The lens seems to be perfectly happy providing that the next press of the focus involves a significant shift in focus distance and will also servo focus on significant distance changes. Not sure how long these needs to be but if it's just 2 to 3" it's very likely not to refocus and if the focus button is released and pressed again it doesn't do anything at all. The focus warning light may even come on.

The other thing that can happen is that the focus squares in the viewfinder show but when the shot is taken it's out of focus slightly and the preview show where it thinks the camera has focused. This seems to happen at times when the distance changes are even smaller.

My old Canon 75-300mm does what I would expect it to do even though it probably has lower optical quality. I haven't taken many shots with it this way but I can hear it shifting focus so at least it's trying. Probably not as often as it should but it's an F4 - 5.6 lens. Probably around F5 when I tried it on the same tests,

To be honest some of this makes me wonder exactly how AF works. I do know the principle but wonder if it actually goes either side of the correct point and then settles in the middle. Maybe the Sigma lens isn't doing that when there are marginal changes and just stays were it is. Marginal isn't the right word though when it can missfocus entire birthday cards even at F13 at about 2 to 3m.

John
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[William W]

Was the release date of this particular model Sigma lens prior to the release date of the EOS80D, but after the release date of the EOS100D?

I think the above is very likely: if yes then I suggest that the particular lens is not fully compatible with the EOS 80D.

Third party Lens Manufacturers need to make their lenses backwards compatible and the scenario where an existing Sigma lens(es) will not function either at all or with minor glitches, with a new model Camera has happened before.

One most notable series of events saw Sigma offering free 're-chipping' of many of their lenses to suit newer model Canon cameras - and even then for some Sigma lenses it was impossible to do.

WW

[ajohnw]

I think there are 2 problems Bill. One as you mention which seems to be down to the lens refusing to focus when told to as the camera picks up that it's out of focus. This could be down to Canon not telling Sigma lenses to do it but is hopefully just down to some new command. Maybe a focus peaking command has been introduced as the large change focus is fine. So fine that for quick rough distance setting it might pay to deliberately focus some distance away first at times.

The other is down to AF as the camera has shown in focus when it's just out. This seems to happen when contrast is rather low. The 5DIII might do this as well but I would need to try it more to be sure. I think it's a software problem. When I release the focus and activate it again the camera should go back to square one but it doesn't seem to. I'd guess that what happens in this situation is that the AF detects similar sized errors each side of focus and then tells the lens to go "mid way". In quotes as I mean something along these lines. It might explain why lens focal distance data seems to be needed in the lens and can be wrong going on Sigma's USB dock.

Thanks for commenting Geoff. I hoped you would as I remember you switching to the 180mm - a bit rich for me so went for the 150 as with the converter I know from my M 4/3 set up that circa 200mm focal length working distances are ok. Not sure about some aspects of the 80D. Maybe I should keep the D7000 and have bought the 180 but I find I prefer lenses weighing not much more than 1kg.

John
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[chauncey]

I might be unusual but, although I'm a Canon user, I have never used AF with my 180 macro.

[ajohnw]

I just expect AF to do what it states on the can WM - AF. In macro terms I know that trimming is needed but at some distances and some target sizes the lens should in my opinion AF pretty well. Say 1.5m or more. I'd say that it can be a bit dubious at that distance if for some reason it's just focused at a similar distance or say panning around a bunch of flowers with the AF active

John
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[DanK]

I just expect AF to do what it states on the can WM - AF. In macro terms I know that trimming is needed but at some distances and some target sizes the lens should in my opinion AF pretty well. Say 1.5m or more. I'd say that it can be a bit dubious at that distance if for some reason it's just focused at a similar distance or say panning around a bunch of flowers with the AF active

John
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It should focus well at much closer distances. I can put my camera on AI servo, turn the AF on on my main macro lens (Canon 100mm L), and move the camera around an irregular surface at a distance of a few inches, and it will lock focus when anything with sufficient contrast comes into the field. It is slower than some lenses at greater distances, but it is still reliable. This is not a macro issue. From all that you have described, it seems like a problem with that particular lens, perhaps only in combination with certain bodies.

[ajohnw]

The 80D is a bit of a crippled camera by the look of it Dan. Stupidly so for it's intended market in my opinion, As for instance no real AF assist light - they mention it for red eye reduction and suggest people in the shot look directly at it. Easiest way to get it to come on is to pop up the flash and then half press the shutter. It's a very weak beam as it's very very wide. Makes no impression at all in our living room lighting which is pretty dim. The 5DIII did flash it's AF assist beam at times when I was trying that. The reviewers see the 80D as being in no mans land but largely in relation to video. My impression is that maybe in some ways the same could be said about photography. I need to use it more and for my intended use I don't think I have seen any problems - yet.

I just tried the same thing as you mention at macro distances. Focused down the garden first. It snapped into focus on the middle of a card. When I shifted the view upwards which decreased the distance a bit it didn't track and plenty of contrast. That was using the shutter button. Then tried the same thing again with the focus on button and it did track. I think I may have an explanation now. The contrasting areas are bigger close up. It even tracked on a card that it just wouldn't handle panning card to card from 2m. The distance change problem is still there though. Crisp focus if the previous distance was further away. May not be the case if very similar but on one occasion 3 rapid presses of the focus on button did achieve focus. I've noticed that cameras may take notice of rapid focus on presses -D7000 for instance will shift focus points when they are all on.

I may be a happy man now.

I did wonder about the Canon 100mm L macro but I have used that length before and prefer longer. I was probably influenced by the 60mm Olympus macro lens as well - great lens but often very difficult to use at a true 1:1 or even near that. Sigma did do a macro lens for the early 4/3 format. 100mm so if they go in that direction I doubt if it will be a long one. If Canon update their 180mm with IS it will probably cost a fortune and be very fast and heavy. On Olympus I have been using the 75-300mm with a close up lens to get round the working distance problems. At times the close up lens needs taking off which is a pain. It can give pretty good results but for some reason I feel I should have APS about. I am really not sure why. Worse still there have been few insects this year where I have been looking for them.


John
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