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

[george013]

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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Red eye reduction is a pre-flash. I don't think continuous focusing is possible with a flash. Not sure about that but it seems unlogic to me.
I don't have a Canon but I did some search https://www.youtube.com/watch?v=7zt67UjXNWA
It could explain your problems with focusing, continuous focusing.

George

[ajohnw]

This is said light



If you look at it's 2nd function I suspect you will see why the light output is rather weak.

John
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[george013]

This is said light



If you look at it's 2nd function I suspect you will see why the light output is rather weak.

John
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Strange. I looked in the manual. I hardly can believe it's working like that.

I just saw that the used camera in the video link isn't a Canon.

George

[ajohnw]

I suspect it's a new idea for Canon George. Could be a crazy one. I don't find it all that unusual for a camera to need it's af assist lamp on. For red eye reduction they mention that subject should look directly at it. Fine but the usual pre flash is more likely to work over a wider range of circumstances.

To me the usual assist light is needed because in terms of low light work the sensors are usually way more capable than the AF. The sensor will take decent images in low light conditions. In fact I never use flash unless I need to especially on people. I normally just use it to get higher shutter speeds or a bit of a fill in.

Maybe the brief use of the flash they mention will work but my initial impression is that if that is used it will use the flash when the shot is actually taken. So far the red eye reduction lamp has only come up when the flash is popped up. That makes sense but if I have to take a flash photo to get it's af assist to work - oh dear. It doesn't mention that the flash is being used for af assist just that it may fire briefly when the camera is used in the dark.

John
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[William W]

John,

I understand that you are concerned about the problem you are having with your Sigma lens.

I am asking you a simple question the answer to which might be relevant to your problem.

What Focus Mode do you have the Camera set to?

Is it set to "ONE SHOT - AF"

WW

[ajohnw]

Currently no Bill. It's set to A1 Servo. I have tried the others - One shot and A1 Area. I thought one shot just did what I would expect. Area seems to relate to tracking and the menu does offer alternative styles of that even when it's set to servo. In servo these don't seem to do anything. I've mostly been reading a downloaded pdf. I think that the printed manual may a have a little more in it.

There is a comment about One Shot. It will switch automatically to A1 Servo if the subject moves.

The notes on the flash derived af assist are confusing. Camera set to basic modes, scn, macro etc it wont come on in A1 Servo. In the creative zones it suggests it will fire as needed . I need to look into that more but haven't noticed a flash off option yet. What it does state seems to mean that the flash must be on in order to obtain the AF assist. Maybe not in creative modes. Aperture, Speed modes etc.

My wife has taken her birthday cards down now so need to set up some fresh targets.

John
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[ajohnw]

Retest one. As Bill I suspect thinks one shot behaves a bit differently but still a little strange. I've only tried the single central point so far. The flash derived af assist does work with the flash popped up and turned off. That isn't in the info display so needs to be done in the menu's.

No problem with significant subject distance changes but not so good just moving along the target and AFing on each one. It shows the same signs as servo - allowing a shot as the AF warning light isn't flashing when it's touch out of focus but sometimes it beeps and a square lights up and is in focus. Sometimes the focus warning flashes. The blue items are worst in terms of not focusing followed by areas of the photo and for some reason the "dogs dinner". That isn't a terribly sharp item.

My latest targets are these



Sorry about the ongoing plastering and I added the 100% res pastes to show how a 2003 lens performs. The small black square is the sigma on the side of the lens hood in the shot. The lens is the 24-85mm forerunner of the 24-105mm taken with flash to avoid having to set up a tripod.

It's having problems with the blue items and some of the others. Generally gets all of them if a significant distance change. Hard to point the camera at items then as the view is so fuzzy. I have to look for blurred colour to pick them out. The distance change I have used is about 15ft.

Actually it would be fair to say that any one of the targets could be iffy at times. Some always.

John
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[William W]

Currently no Bill. It's set to A1 Servo.

John,

It is absolutely pointless performing any tests on the accuracy and speed of a specific EOS camera and lens combination's ability to Auto Focus using Static Subjects if the FOCUS MODE is set to AI SERVO.

To perform thew tests that you have been describing throughout all of this conversation, the AF Drive mode MUST be set to "ONE SHOT AF"

Please note that the latest test shot (Post #47), the EXIF of that image reports the Auto Focus Drive was set to AI SERVO. Having the AF Drive set to AI SERVO would explain much of the difficulty that you describe in your comments of that post.

WW

Footnote:

BTW, FYI and for clarity of meaning and understanding:

The terms are: "AI SERVO" and "AI FOCUS". That is, the capital letters "A" and "I"; and not the letter "A" and the numeral "1"

"AI" is an acronym for Artificial Intelligence.

[ajohnw]

Using the flash derived af assist didn't make any difference to the testing so it looks like light levels need to be a lot lower for that to be needed. The 5DIII did use it's light in servo mode when one of the cards was in frame for several seconds and still. The 80D wont use it in that mode. In other modes it will always emit if the flash is up even when pointed out of the window. Haven't tried that mid day etc but I suspect it will still do it even if not needed.

The menu items for AF seem to apply to live view only and it looks like auto switching from one shot to servo may only happens in basic mode. In the others there are 2 variations of one shot. Normal and auto switching to servo mode if the subject moves. That one is called A1 Focus.

One thing that does make it focus just about every time is deliberately manually blurring the subject significantly. I suspect that may work in A1 Servo as well. I could say 100% of the time but daren't.

This is what it states about focus in A1 Servo

With AI Servo AF, the beeper will not sound even when focus is achieved.
Also, the focus indicator <o> in the viewfinder will not light up.


I feel that I am getting that sort of behaviour in the other modes when only slight focus distance changes are needed. Some black AF squares and no red ones along with a beep. Be interesting to see what happens when I set first shot focus priority and I need to try a Canon lens again.

I have cross posted with Bill so just a note. I'm getting the same behaviour in all modes. The shot I posted - yes but it has focused as it should. If the focus of the lens had been pretty close to what was needed it probably wouldn't have what ever mode it was in. However as it was a Canon lens I took the shot with that may not be the case.

John
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[ajohnw]

Well just about finished now. As I have been testing it the 2003 Canon 75-300mm seems to be rock solid in all focus modes. I've been setting it just over 200mm to match the Sigma 150mm macro with converter so the main difference is that it's a bit slower lens.

The Sigma is mixed. In modes that do offer a confirm it has never confirmed on all targets. When it's missing a number of them the contrast and distance change gets to a point where it does refocus. That is when it's missed most of them. If it's just missing one or two it stays like that. Deliberately miss focusing manually always causes the focus to correct and confirm. I've only tried that from a rather blurry view.

In AI servo the viewfinder focus light may flash if it isn't correctly focused when first shot focus priority is set. The absence of the flash doesn't seem to guarantee a good precise focus. When first focus priority is set I feel the focus confirm should send the squares red just like it does in the other modes and also if 2nd shot and so on focus priority is set. It's difficult to see the squares on some colours such as black or in dim light. I'd guess they may not do this because it may miss focus but that's a nonsense when 1st shot focus priority is set.

I tried AI servo walking towards a target. Both lenses did change focus at some point. Not possible to get any idea of what the quality of the results would be in real life. I may try that on local trains some time soon.

Now I have a decent idea of what is actually going on I can phone Sigma and see what they say. From what I can see it always focuses spot on when there is a significant focus distance change so the problem can't be anything to do with lens calibration.

To make matters worse I have just received a Tokina 12-24mm a little early for my birthday - wonder what that will do.

John
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