EFs 24mm Pancake Strange Auto Focus Behavior

[BurnUnit]

Recently got a Canon refurb EFs 24mm pancake lens. But now I'm not sure if it's acting up on me or not. While taking some photos of the sign below the autofocus acted strangely.

I composed the shot and focused using the back button and the image went completely blurry as the lens attempted to focus to a minimum distance. Released and hit the focus button again and nothing moved in the lens. Manually focused to infinity and tried again but got the same results. All this happened with the camera in vertical position and aimed upward from ground level. Powered the camera off and back on, turned the body both horizontal and vertical, aimed it straight ahead at the building and the auto focus worked just fine and has ever since then.

The camera is a 60D that I've had since new and it's never done anything like this with any of my other Canon lenses. I can't imagine that aiming the camera upwards or turning it vertically should have any effect on auto-focusing. The only other thing that I thought of after the fact was that I was shooting in multi-point focus mode. Could all the plain blue sky in the background make things play up like this, even though there were at least a couple focus point on the sign itself? Or is it time to contact Canon Service even though i've not been able to duplicate this odd behavior since?

[RobertTheFat · Accepted solution]

I think your supposition that the sky is the culprit is probably correct. A plain blue sky lacks an object, preferably a contrasty object, to focus on. It's even more likely if you're using live view, which has to rely on contrast-detect autofocus.

If you were manually focusing, you'd just set the lens to infinity. But the autofocus mechanism lacks an innate understanding of what or where infinity is.

[Waddizzle · Accepted solution]

Yeah, Bob is right.  Make sure that you focus on something, not the blank sky.

Is this your first STM lens?  They do seem to behave a little differently from non-STM lenses on occasion.  But, I think the difference is a reflection of how fast they focus.  It just might be focusing so fast that the 60D misses it.  In other words, the camera body is missing the focus, not the lens.  Focus is blowing by so fast, that the camera misses it.

I know I have had similar problems using STM lenses on my T5 with the EF-S 24mm STM and the EF 50mm STM.  The first thing I noticed about either lens was how fast they focused compared to the kit 18-55mm lens.  I tried the EF 50mm STM on my 6D, and had no problems.  Put it back on the T5, and it would occasionally miss detecting focus and being to hunt.

One of the benefits of back button focus is that you can focus a shot, recompose it, and not worry about the camera refocusing when you press the shutter.  I use it focus on birds sitting in trees, hiding among the branches and leaves.  

[ebiggs1 · Accepted solution]

"Or is it time to contact Canon Service even though i've not been able to duplicate this odd behavior since?"

I am not a fan of the pancake lenses but even good lenses miss focus once in awhile.  Or, focus on something other than what you thought.  One shot doesn't prove or disprove anything.  Shoot more.

[TTMartin · Accepted solution]

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@BurnUnit wrote:

Recently got a Canon refurb EFs 24mm pancake lens. But now I'm not sure if it's acting up on me or not. While taking some photos of the sign below the autofocus acted strangely.

I composed the shot and focused using the back button and the image went completely blurry as the lens attempted to focus to a minimum distance. Released and hit the focus button again and nothing moved in the lens. Manually focused to infinity and tried again but got the same results. All this happened with the camera in vertical position and aimed upward from ground level. Powered the camera off and back on, turned the body both horizontal and vertical, aimed it straight ahead at the building and the auto focus worked just fine and has ever since then.

The camera is a 60D that I've had since new and it's never done anything like this with any of my other Canon lenses. I can't imagine that aiming the camera upwards or turning it vertically should have any effect on auto-focusing. The only other thing that I thought of after the fact was that I was shooting in multi-point focus mode. Could all the plain blue sky in the background make things play up like this, even though there were at least a couple focus point on the sign itself? Or is it time to contact Canon Service even though i've not been able to duplicate this odd behavior since?

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You mention that you are using Back Button Focus. 

What focus mode are you in One Shot or AIServo?

Keep in mind Canon's Auto AF Point Selection (multi-point focus mode) modes work completely differenty in One Shot and AIServo.

In One Shot the camera will focus on the closest item under an active AF point that has sufficient contrast.

In AIServo the camera will use the designated AF point initially and then hands off to the other AF points if the subject moves off the designated AF point. The starting AF point defaults to the CENTER AF point and the starting point is only selectable in higher end cameras. A couple of Canon cameras like the 7D Mk II allow you to set auto acquisition of the initial AF point in AIServo, but, that requires a menu setting. 

So if you are in AIServo the camera is trying to focuse with the center AF point, and there is nothing with contrast under the center AF point to focus on.

[BurnUnit · Accepted solution]

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@Waddizzle wrote:

Yeah, Bob is right.  Make sure that you focus on something, not the blank sky.

Is this your first STM lens?  They do seem to behave a little differently from non-STM lenses on occasion.  But, I think the difference is a reflection of how fast they focus.  It just might be focusing so fast that the 60D misses it.  In other words, the camera body is missing the focus, not the lens.  Focus is blowing by so fast, that the camera misses it.

---

My EFs 10-18 is an STM lens also. They do  focus quickly but the 10-18 has never reacted like this. But shooting mostly on the wide end of it if I have it stopped down very much I think it tends to just go to infinity and says "close enough". I'll have to try shooting some wide open big blue sky shots with it and see if can get it to act up.

[RobertTheFat · Accepted solution]

I think your supposition that the sky is the culprit is probably correct. A plain blue sky lacks an object, preferably a contrasty object, to focus on. It's even more likely if you're using live view, which has to rely on contrast-detect autofocus.

If you were manually focusing, you'd just set the lens to infinity. But the autofocus mechanism lacks an innate understanding of what or where infinity is.

[BurnUnit]

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@RobertTheFat wrote:

I think your supposition that the sky is the culprit is probably correct. A plain blue sky lacks an object, preferably a contrasty object, to focus on. It's even more likely if you're using live view, which has to rely on contrast-detect autofocus.

If you were manually focusing, you'd just set the lens to infinity. But the autofocus mechanism lacks an innate understanding of what or where infinity is.

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Well that was the only explanation tha made any sense to me at the time. As far as "an innate understanding of what or where infinity is", I barely understand it myself! This may be the first time I've felt that the camera wasn't smarter than me.

[Waddizzle · Accepted solution]

Yeah, Bob is right.  Make sure that you focus on something, not the blank sky.

Is this your first STM lens?  They do seem to behave a little differently from non-STM lenses on occasion.  But, I think the difference is a reflection of how fast they focus.  It just might be focusing so fast that the 60D misses it.  In other words, the camera body is missing the focus, not the lens.  Focus is blowing by so fast, that the camera misses it.

I know I have had similar problems using STM lenses on my T5 with the EF-S 24mm STM and the EF 50mm STM.  The first thing I noticed about either lens was how fast they focused compared to the kit 18-55mm lens.  I tried the EF 50mm STM on my 6D, and had no problems.  Put it back on the T5, and it would occasionally miss detecting focus and being to hunt.

One of the benefits of back button focus is that you can focus a shot, recompose it, and not worry about the camera refocusing when you press the shutter.  I use it focus on birds sitting in trees, hiding among the branches and leaves.  

[BurnUnit · Accepted solution]

---

@Waddizzle wrote:

Yeah, Bob is right.  Make sure that you focus on something, not the blank sky.

Is this your first STM lens?  They do seem to behave a little differently from non-STM lenses on occasion.  But, I think the difference is a reflection of how fast they focus.  It just might be focusing so fast that the 60D misses it.  In other words, the camera body is missing the focus, not the lens.  Focus is blowing by so fast, that the camera misses it.

---

My EFs 10-18 is an STM lens also. They do  focus quickly but the 10-18 has never reacted like this. But shooting mostly on the wide end of it if I have it stopped down very much I think it tends to just go to infinity and says "close enough". I'll have to try shooting some wide open big blue sky shots with it and see if can get it to act up.

[ebiggs1 · Accepted solution]

"Or is it time to contact Canon Service even though i've not been able to duplicate this odd behavior since?"

I am not a fan of the pancake lenses but even good lenses miss focus once in awhile.  Or, focus on something other than what you thought.  One shot doesn't prove or disprove anything.  Shoot more.

[BurnUnit · Accepted solution]

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@ebiggs1 wrote:
One shot doesn't prove or disprove anything.  Shoot more.

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Yep. I intend to try to get the lens to predictably act that way again just to prove it to myself. Another case of improving the photographer rather than the camera.

[TTMartin · Accepted solution]

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@BurnUnit wrote:

Recently got a Canon refurb EFs 24mm pancake lens. But now I'm not sure if it's acting up on me or not. While taking some photos of the sign below the autofocus acted strangely.

I composed the shot and focused using the back button and the image went completely blurry as the lens attempted to focus to a minimum distance. Released and hit the focus button again and nothing moved in the lens. Manually focused to infinity and tried again but got the same results. All this happened with the camera in vertical position and aimed upward from ground level. Powered the camera off and back on, turned the body both horizontal and vertical, aimed it straight ahead at the building and the auto focus worked just fine and has ever since then.

The camera is a 60D that I've had since new and it's never done anything like this with any of my other Canon lenses. I can't imagine that aiming the camera upwards or turning it vertically should have any effect on auto-focusing. The only other thing that I thought of after the fact was that I was shooting in multi-point focus mode. Could all the plain blue sky in the background make things play up like this, even though there were at least a couple focus point on the sign itself? Or is it time to contact Canon Service even though i've not been able to duplicate this odd behavior since?

---

You mention that you are using Back Button Focus. 

What focus mode are you in One Shot or AIServo?

Keep in mind Canon's Auto AF Point Selection (multi-point focus mode) modes work completely differenty in One Shot and AIServo.

In One Shot the camera will focus on the closest item under an active AF point that has sufficient contrast.

In AIServo the camera will use the designated AF point initially and then hands off to the other AF points if the subject moves off the designated AF point. The starting AF point defaults to the CENTER AF point and the starting point is only selectable in higher end cameras. A couple of Canon cameras like the 7D Mk II allow you to set auto acquisition of the initial AF point in AIServo, but, that requires a menu setting. 

So if you are in AIServo the camera is trying to focuse with the center AF point, and there is nothing with contrast under the center AF point to focus on.

[BurnUnit]

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@TTMartin wrote:What focus mode are you in One Shot or AIServo?

Keep in mind Canon's Auto AF Point Selection (multi-point focus mode) modes work completely differenty in One Shot and AIServo.

In One Shot the camera will focus on the closest item under an active AF point that has sufficient contrast.

In AIServo the camera will use the designated AF point initially and then hands off to the other AF points if the subject moves off the designated AF point.

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It was in One Shot mode which is where the camera spends most of its time. But AIServo looks like another mode I need to do some experimenting with.

Thanks for everyone's help! I think I'm well on my way to believing that the lens is working exactly as should be expected under the circumstances. I've had the 60D for six years now and the reason I've kept it this long is because it will still do 99% of everything I need it to and I'm still learning more about its capabilities. That and the tilt-swivel LCD!