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

Considering the tremendous throw of macro lenses, at least with my 180, is it any wonder
that AF would be a problem.

John,

I just did a little more experimenting with mine. I think I now understand part of what you are experiencing.

Some of what you describe may be a compatibility problem, but I think part of it may be expected. You wrote:

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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.

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I don't think this has anything to do with which button you use. When you change buttons, you aren't changing how the camera behaves; you are simply changing which switch sends the signal.

Here's what I just tried with one of my setups. I used a 5D III set for the lens to work even if focus is impossible. I put on my 100mm macro, with the focus limiter set to "full," so it shouldn't stop focus. I used back button focus, as I almost always do. I set the AF to AI Servo. I set the AF to center point with 9-point assist.

Then I tried two things, repeatedly.

1. I focused on something about 12 ft. (3.7 m) away. Holding the shutter down, I moved the camera to focus on something about4 inches (20 cm) away. No problem. It was slow to change--it's a huge change in focus, and the AF in macro lenses isn't fast--but it focused accurately each time.

2. I did exactly the reverse. In each case, it initially failed to focus on the distant subject. When I hit the AF button again, it focused just fine.

Here's what I think is going on. The difference in focusing distance was so huge that when I pointed to the distant surface, it was tremendously blurred. I think the camera, sensing no contrast in the AF areas, simply stopped, despite the camera's settings. When I hit the button again, it resumed, and it continued (slowly) on its way until it focused.

There was no AF assist light in this case.

So here are my suggestions:

-- Simplify your tests. A lot of what you have been wrestling with is probably irrelevant. All you need to test this is things to focus on in a well-lit environment, the lens, and the body. it should be fine to leave the body on back-button focus.

-- Test the lens-camera combination at the distances you will use them. I have been shooting macro intensively for about 8 years, and I never noticed #2 above before today. I have never once had reason to put the camera in AI servo and quickly switch focus from a macro distance to 4 m. Given my use--I sometimes use my macro as a short telephoto--I would test it for both macro use and as a telephoto, not for switching between them in the middle of a shot.

-- Make sure that the combination can adjust focus appropriately within each of those ranges. If it doesn't work within the macro range, for example, you probably have a lens/camera compatibility problem or an equipment failure. I doubt very much it is a problem of the 80D as a type, as I had no problems using a 50D and before that an XTi for macro work, and they are much inferior in terms of AF.

Dan

What I am left with is where I came in on this. Ancient Canon 75-300mm best they could produce when it was made tries to focus when scanning the cards from about 6ft. Sigma doesn't. The zoom was set at just past 200mm so view the same as sigma plus 1.4x. It will have been at around F5 at that. Sigma faster at F4 so errors should be more clearly shown as far as the camera is concerned. The zoom is F4 at 75mm, 5.6 at 300mm.

:D I used about 6ft this time as it's more accurate. As far as ISO is concerned I'd need to say about 1800mm or about 1.8m. If I sinned by using cms it would have the same implications.

I've booked a return with sigma but want to talk to them first in case sending it back for an update could be a waste of my time.

John
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Originally Posted by ajohnw

. . . I've booked a return with sigma but want to talk to them first in case sending it back for an update could be a waste of my time.

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I am interested to know the outcome.

Good luck.

WW

John,

I'll throw in some observations regarding AF response with my Nikon stuff, they may or may not give a clue and they may show that AF is not always foolproof or works the way you would expect it to.

1) When adding a Nikon 1.4TC to a Nikon 80-400 mm not all AF modes are available. (and this is all modern kit). TC not used for the below test/observation.

2) With that lens set at 200 mm and a sharp target (jutting out window frame edge) 3 m away and another target (sharp lamp post edge) 50 m away to the side;

a) In 'Single point focus' (centre one) with AF-On continually pressed (BBF) moving between the the window frame and lamp post the AF responds perfectly as you would expect going back and forth between the two targets.

b) In 'Dynamic 9 or 21 point AF' (the mode where the points around the 'selected' one detect movement) the AF does not respond when moving from the near target to the far target (but shows as in focus) and vice versa. When moved to the far target which remains OOF and re-pressing BBF the AF reacts immediately (and the same when going in the opposite direction).

Reading through your posts and settings I'm a bit confused and as Dan has said perhaps you need to simplify your tests.

In the first instance I would undertake similar to the above using 'Single Point' (centre) only and 'Continuous AF' and note the response. If the result is good, move on to the other AF point modes.

John - I haven't re read the whole conversation and you might have already stated this as a fact, but, please confirm that the Auto Focus MODE is set to "One Shot - AF".

My point being is, that if the AF MODE is set to either: "AI Servo AF"; or "AI Focus AF", then there are other issues that we probably need to consider.

WW

Canon seem to call it A1 Area Mode / Flexi Zone as more than one focus point is being used. I've been using 9 points in the middle of the screen. There are associated settings to alter the tracking capabilities. The main one is the facility to delay a focus change if something passes between the point the camera is focused on and the camera. That's been set to very responsive. Also a setting for jerky movement rather than smooth which I assume turns off any prediction. It's also possible to turn of colour tracking. I've tried both and no difference. A1 Servo doesn't exist in the menu's after all of this is set but does appear in the LCD on top of the camera. If I now set one central point nothing changes. It behaves the same way.

The main aspect really is that a Canon lens does one thing and the Sigma does something else.

No signs of one shot AF in the menu's either.

Later I can do a completer reset and see what appears but as the camera comes Canon seem to have handled one shot AF in an odd sort of way. It has a back focus button that is active. 1/2 press of the shutter activates focus as well - that I assume is the one shot. It seems messy to me as the camera will focus again back button released when the shutter button is pressed. There is a video that suggests assigning half press to something else for using just the back button. Canon don't offer an option to ignore it.

Yes - my first thoughts was look for a firmware upgrade but there isn't one.

There are 2 options shown in the viewfinder on the central block of AF points. A square or individual dots. The menu also adds a face. I've tried all. No difference. The items that I have pointed the camera at and noticed the behaviour all fill the central af area / are out of it when I pan.

When I reset settings and start over again I don't expect anything to change as apart from re assigning the half shutter button press I didn't change anything quickly. I should make sure that this is really needed but my impression was that it is.

John
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John, considering the compatibility aspect of the Sigma to your Canon I wonder how that could be a problem?

The lens passes light through to the AF sensor within the camera, the result from the camera simply sending a signal back to the lens to revolve one way or the other. At some point the lens is told by the camera to stop revolving when the camera thinks it's in focus.

So in other words the camera either Auto-focuses with that lens or not at all I would assume.

I've always wondered exactly how camera's phase detect focus works Grahame. I suspect it's a bit more involved than that. If you look at reviews of the sigma usb doc you will see that it allows a lens to be tweaked at 4 focus distance settings. Some mention that this can help the phase contrast AF focus more accurately. This leaves me thinking that the camera or lens needs accurate rate of focus change information or something like that.

What's a bit weird about the problem I have come across is that a Canon lens on the market in 2003 tries to AF and the Sigma lens new earlier this year doesn't. This is when just marginal changes are needed. Or better put it will focus cleanly given that the distance change is sufficient. I'm not sure how much that needs to be. There are a few comments about on the web concerning focus problems with the 150mm. I've not looked at the 100 and Geoff reckons that the 180 focus isn't always accurate - I think he said accurate at a distance.

I've been out most of the day and have a few things to do but just looked at the camera but just the AF select button and the lcd panel on the top of the camera. There I have one shot, A1Area and A1 Servo. That doesn't match what is available in the menu's.

I've flattened the battery playing around so need to charge it now.

John
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Quote:

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Originally Posted by ajohnw

I've always wondered exactly how camera's phase detect focus works Grahame. I suspect it's a bit more involved than that. If you look at reviews of the sigma usb doc you will see that it allows a lens to be tweaked at 4 focus distance settings. Some mention that this can help the phase contrast AF focus more accurately. This leaves me thinking that the camera or lens needs accurate rate of focus change information or something like that.

What's a bit weird about the problem I have come across is that a Canon lens on the market in 2003 tries to AF and the Sigma lens new earlier this year doesn't. This is when just marginal changes are needed. Or better put it will focus cleanly given that the distance change is sufficient. I'm not sure how much that needs to be. There are a few comments about on the web concerning focus problems with the 150mm. I've not looked at the 100 and Geoff reckons that the 180 focus isn't always accurate - I think he said accurate at a distance.

I've been out most of the day and have a few things to do but just looked at the camera but just the AF select button and the lcd panel on the top of the camera. There I have one shot, A1Area and A1 Servo. That doesn't match what is available in the menu's.

I've flattened the battery playing around so need to charge it now.

John
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Have a look at this site. I found it by accident a couple of years ago and was much helpful giving me info about some Nikon-lenses. http://www.mir.com.my/rb/photography...ing/index2.htm

I found it quite difficult to navigate in this site, you've to find out yourself.

George

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Originally Posted by ajohnw

I've always wondered exactly how camera's phase detect focus works Grahame. I suspect it's a bit more involved than that.

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John, I'm sure there are a number of differences with the actual camera AF sensor but the reality is that something has to detect OOF, then send a signal to the lens to move/adjust focus, then something has to tell the system all's OK and focus has been achieved (shown by that little indicator light). This is disregarding slight discrepancies with front/back focus.

I just did an interesting test with an optically good and usable 105 mm Nikon macro that has had all its electronics removed. The 'in-focus indicator light' in the camera viewfinder did not work as you would expect suggesting that this function relies upon some form of feedback from the lens.

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Originally Posted by ajohnw

If you look at reviews of the sigma usb doc you will see that it allows a lens to be tweaked at 4 focus distance settings.

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I have had a read up on the system and this allows what would be a linear signal simply offset if wanted by the camera 'AF Fine tune/micro adjust' function to one that could be changed to a 4 point curve/wave across the focus distance range. Clever:)

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Originally Posted by ajohnw

Some mention that this can help the phase contrast AF focus more accurately. This leaves me thinking that the camera or lens needs accurate rate of focus change information or something like that.

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It will certainly allow a better final result.

Quote:

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Originally Posted by ajohnw

What's a bit weird about the problem I have come across is that a Canon lens on the market in 2003 tries to AF and the Sigma lens new earlier this year doesn't. This is when just marginal changes are needed. Or better put it will focus cleanly given that the distance change is sufficient. I'm not sure how much that needs to be. There are a few comments about on the web concerning focus problems with the 150mm. I've not looked at the 100 and Geoff reckons that the 180 focus isn't always accurate - I think he said accurate at a distance.

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Agree this is pointing to something being strange with the Sigma.

Quote:

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Originally Posted by ajohnw

I've been out most of the day and have a few things to do but just looked at the camera but just the AF select button and the lcd panel on the top of the camera. There I have one shot, A1Area and A1 Servo. That doesn't match what is available in the menu's.

I've flattened the battery playing around so need to charge it now.

John
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I look forward to seeing the progress of this one...........................

Interesting site George. It actually mentions distance. This one does as well after a fashion as well but there are a number of links to follow.

https://www.dpreview.com/articles/54...tion-autofocus

John
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There is a bit more rambling details on AF on this one and more on the Stanford link at the bottom, Part 2 of the dpreview is interesting where he compares cameras and lenses.

https://www.dpreview.com/articles/54...tion-autofocus

The cameras do seem to tell the lens where to focus and it seems might tell it to do the same thing again if after it's done it the first time it's still out.

I've cleared all of the 80D's settings but time for bed. It seems to be only offering me several area AF options in the menu's but does offer servo af via the af mode button. Maybe I should phone Canon and ask just when are they going to finish the firmware in the camera ? Now it's all cleared single centre point doesn't work very well at all. The central block looks to be as before. The focus now button does focus the camera but say that was used to focus something in the view, released and the camera panned and the shutter button pressed to take the shot - it refocuses.:eek:

John
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Quote:

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Originally Posted by ajohnw

The focus now button does focus the camera but say that was used to focus something in the view, released and the camera panned and the shutter button pressed to take the shot - it refocuses.:eek:

John
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Here's a video that tells you how to 'deactivate' the shutter button from the 'focus' function.

John,

I read your link. I think it's wrong. When I change subject while focusing, it focuses on the last subject. In AF-s.

When your shutter button is associated with focusing, it will refocus when you use the back button for focusing. You must deactivate that as Graham tells you.

Bur why not making it simple. Go back to the shutter functions, the basics. No converter. And do your research. If you're sure about a good functioning in that situation, you can expand it.
Make sure you only use 1 focus point, in the middle. You know about the impact of the contrast. But also the lines, vertical or horizontal, might matter.

I mentioned before, my Sigma 105 has been brought back to the shop to get it repaired. It still acts different as my Nikon lens.

George

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Originally Posted by William W

John - . . . please confirm that the Auto Focus MODE is set to "One Shot - AF".

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Originally Posted by ajohnw

. . . No signs of one shot AF in the menu's either. . .

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The AF DRIVE MODE is set separately to setting the AF Point Selection and is not via the menus but by depressing the AF BUTTON and then making the AF DRIVE selection via the MAIN DIAL (on top just behind the Shutter Release), or the QCD - Quick Control Dial (at back of Camera).

See Chapter 3 of the User Manual (Begins at p115).

Specifically PP116 ~ 117 to set ONE SHOT - AF.


REF:

http://gallery.photo.net/photo/18279511-md.jpg

http://gallery.photo.net/photo/18279512-md.jpg

WW

Images Copyright Canon International, reproduced here for educational purposes.

I mentioned that there is a video showing how to deactivate the shutter button focus earlier. To me is seems a little silly supplying the camera with the default settings as they are. AF on button and the shutter button active as well especially how people often use back button focus. They would be inclined to think that focus will lock if it's not pressed. It will until the shutter is pressed if in a continuous mode. I have no interest in switching to one shot to make it stop doing that. None what so ever. One missing option on the 1/2 button press appears to be off. I just followed the video suggestion. I am going through it all again just to be sure.

;) i haven't got round to locking exposure and focus separately but compensation can also take care of exposure but not as well as on some mirrorless cameras.

I think there is a bit of confusion Bill. I know that is the way to select those 3 focus modes - it appeared to be the only way. The menu's just offer 3 versions of area focus. Face, ( ) or [ ]. I should read up the difference between ( ) and [ ]. Any way using the LCD panel is not a pleasant experience for some one that needs reading glasses to see what is set in it. I hate them, you can guess why. AF areas can be set via the view finder. AF mode could be too. Fortunately both do appear on the rear display when the info button is pressed.That can throw up 3 different screens.

I'm mainly concerned with the problem with the Sigma lens I have mentioned. However reviews suggest that the 80D is aimed at competing with the cheaper D7200. This seems to be why it has a brand new sensor and low light level AF. I've not used a D7200 but would suspect it's very similar to a D7000 usability wise. On that basis my initial impression is that it doesn't really compete at all. Some reviewers wonder what it really offers as well. It seems it does have more dynamic range than the 7DII but lags a bit behind the D7200. I've seen figures that suggest it's noise levels are better but suspect that's marginal in practice. Live view does have enhancements. I do use that at times but not that often. Touch screen one shot focus is of use to me then. They have improved the AF. I've not looked at what else it offers in live view but wonder if it indicates blown highlights and can offer constant illumination level views for when those are needed. Also at the same level that the actual shot will show. My reason for picking it is mainly the sensor. Low light AF too but I might find that I am rather disappointed with the lack of a focus assist lamp. It may be that the flash can be used for that but not sure if the flash has to fire in the actual shot as well. The 5DIII did use it's focus assist lamp a few times when I was trying the Sigma lens on it but the behaviour was generally as per the 80D.

:) Our living room is lit with lights that provide more of it than a full moon on a clear night. Just in case anyone wonders.

John
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Quote:

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Originally Posted by ajohnw

I mentioned that there is a video showing how to deactivate the shutter button focus earlier. To me is seems a little silly supplying the camera with the default settings as they are. AF on button and the shutter button active as well especially how people often use back button focus. They would be inclined to think that focus will lock if it's not pressed. It will until the shutter is pressed if in a continuous mode. I have no interest in switching to one shot to make it stop doing that. None what so ever. One missing option on the 1/2 button press appears to be off. I just followed the video suggestion. I am going through it all again just to be sure.

;) i haven't got round to locking exposure and focus separately but compensation can also take care of exposure but not as well as on some mirrorless cameras.

I think there is a bit of confusion Bill. I know that is the way to select those 3 focus modes - it appeared to be the only way. The menu's just offer 3 versions of area focus. Face, ( ) or [ ]. I should read up the difference between ( ) and [ ]. Any way using the LCD panel is not a pleasant experience for some one that needs reading glasses to see what is set in it. I hate them, you can guess why. AF areas can be set via the view finder. AF mode could be too. Fortunately both do appear on the rear display when the info button is pressed.That can throw up 3 different screens.

I'm mainly concerned with the problem with the Sigma lens I have mentioned. However reviews suggest that the 80D is aimed at competing with the cheaper D7200. This seems to be why it has a brand new sensor and low light level AF. I've not used a D7200 but would suspect it's very similar to a D7000 usability wise. On that basis my initial impression is that it doesn't really compete at all. Some reviewers wonder what it really offers as well. It seems it does have more dynamic range than the 7DII but lags a bit behind the D7200. I've seen figures that suggest it's noise levels are better but suspect that's marginal in practice. Live view does have enhancements. I do use that at times but not that often. Touch screen one shot focus is of use to me then. They have improved the AF. I've not looked at what else it offers in live view but wonder if it indicates blown highlights and can offer constant illumination level views for when those are needed. Also at the same level that the actual shot will show. My reason for picking it is mainly the sensor. Low light AF too but I might find that I am rather disappointed with the lack of a focus assist lamp. It may be that the flash can be used for that but not sure if the flash has to fire in the actual shot as well. The 5DIII did use it's focus assist lamp a few times when I was trying the Sigma lens on it but the behaviour was generally as per the 80D.

:) Our living room is lit with lights that provide more of it than a full moon on a clear night. Just in case anyone wonders.

John
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I'm not sure if I understood you. It's quite a monologue. The Canon has a focus assist light I think. It doesn't work when you're continuous focusing.

George

Just a note for George.

I have made 100% sure that the 1/4x converter makes no difference at all to focusing behaviour.

The AF links are interesting. It makes a lot of sense for the camera to compute a distance and tell the lens to set it's self to that and then refine if needed. Some people have studied the data that passes back and forth between camera and lens. Initially a Russian who's aim was to make the af confirm indicator work when manual lenses are used on an EOS camera via an adapter. The adapter I have tells the camera that it's a 50mm F1.4 in manual focus mode. I used it on me 5D just before it went in for a service. The report that came back from the service mentioned the last lens used - 50mm F1.4. Some variant of the adapter can have other lenses data entered some how or the other.

After clearing all settings the performance of the central spot alone was terrible - just zipped through the focus point without stopping. I did try pointing the square very accurately as max contrast areas and it made no difference. Going on previous settings selecting a block of af sensors gets round this problem. This to me is unNikonLike. Taking the converter off might might improve central spot only as the image will be a bit brighter. I haven't noticed this happening when I tried various arrangement before though.

John
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It has a red eye reduction light George - a very wide beam so the lighting impact it has is the weakest I have ever seen. I always test some aspects of the cameras I buy in our living room. That includes dark corners - I am not impressed in that area. Just about any camera would need an assist light to focus in them - fine if it has one.

It seems that the flash can be used for focus assist but I have not really tried going into that yet other than with the previous settings. With the flash popped up the red eye reduction light comes on as soon as the shutter is 1/2 pressed. That will be down to my settings, the 1/2 shutter button assignment. As far as I am aware the light levels were too high for the camera to use the flash for AF assist. The manual mentions that the flash may fire briefly when focusing in low light conditions. I need to look at the manual page on possible assignments for a 1/2 press. As mentioned I just used the one suggested in the video.

John
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