EF 40mm f/2.8 issue

[pitchers]

I use the EF 40mm f/2.8 Canon "pancake" lens on a 6D and have an issue. The lens will appear to "focus" on whatever I select in the focus point in the viewfinder but when I press the shutter, it seems to "prefer" whatever is closest in the viewfinder and focuses on that. I've had the lens for a while but just had the oppportunity to use it for a solid week in a very photogenic environment and this drove me nuts!

The exposure also seems very erratic -- many photos are a stop or two underexposed -- with a very sharp cutoff, omitting about a third of the histogram in Lightroom.  The photos that are properly exposed and focused (about half) are lovely but it's so erratic.  It appears to be a communication issue between the lens and the camera.  I've removed and re-seated the lens a few times but no change. For comparison, my 24-105mm f/4 focuses and exposes perfectly, so this seems to be a lens-specific phenomenon.

Any thoughts...?

[Waddizzle]

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@pitcherswrote:

These have all been good photography tips. But does anyone have insight into this particular issue?  It is only with this lens.

"Thanks.  My point is that it is only this lens. If I sit in my chair and shoot through an open interior door (with the door frame still in the field of view), I can focus on a point in the next room but the resultant photo is focused for the doorframe.  If, while sitting in the same chair, I swap on my 24-105 zoom, set it at 40mm(ish), take the exact same photo, I get nice crisp distant focus as intended."

So it's not related to the mode, or any lens-independent user-adjustable camera setting. And no, the lens is not set to MF.

Oh well, was worth a shot.  Thanks, all!

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Try your tests outdoors.  The 6D does not have the smarts to compensate for the flicker of artificial lighting.

[RobertTheFat]

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@Waddizzlewrote:

"Even BBF itself could be part of the problem. On the cameras with which I'm familiar, BBF is not disabled by default; but it is (by default) subject to being overridden by shutter-button focus. You may think you've gotten the subject in focus via the back button; but when you press the shutter botton, the camera may have a different idea."

I have yet to set it enabled, by default, on a camera body.  Reseting custom controls disables it..  The metering system is enabled by default, but not metering and focusing.

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From page 44 of the June 2016 edition of the 5D Mark III instruction manual:

"In the P/Tv/Av/M/B modes, pressing the <AF-ON> button will execute the same operation as pressing the shutter button halfway."

This is confirmed on pages 70, 201, and 228.

[pitchers]

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@Waddizzlewrote:

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@pitchers

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Try your tests outdoors.  The 6D does not have the smarts to compensate for the flicker of artificial lighting.

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It's focus.  Focus problem. Problem with the focus. And just this lens. And the 6D is evidently smart enough with my other lenses, as noted.

Now I know how women must feel!  

I feel like I'm in Ghost.

Did a search and there is a firmware issue from 2012 for this lens but I suspect that this has been long resolved. Mine is < 3 years old. OK, I'll assume it's a bad lens. Thanks; over and out.

[Waddizzle]

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@RobertTheFatwrote:

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@Waddizzlewrote:

"Even BBF itself could be part of the problem. On the cameras with which I'm familiar, BBF is not disabled by default; but it is (by default) subject to being overridden by shutter-button focus. You may think you've gotten the subject in focus via the back button; but when you press the shutter botton, the camera may have a different idea."

I have yet to set it enabled, by default, on a camera body.  Reseting custom controls disables it..  The metering system is enabled by default, but not metering and focusing.

---

From page 44 of the June 2016 edition of the 5D Mark III instruction manual:

"In the P/Tv/Av/M/B modes, pressing the <AF-ON> button will execute the same operation as pressing the shutter button halfway."

This is confirmed on pages 70, 201, and 228.

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Guess what. That’s not BBF.  If the shutter and the button do the same thing, that’s not BBF.  With BBF, pressing the shutter halfway only activates the metering, but not AF.  Not activating AF when you press the shutter is the whole point.  

I find it useful in One Shot mode, such as focusing on a bird among tree branches.  I can focus, and then press the shutter without the camera refocusing.

[RobertTheFat]

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@Waddizzlewrote:

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@RobertTheFatwrote:

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@Waddizzlewrote:

"Even BBF itself could be part of the problem. On the cameras with which I'm familiar, BBF is not disabled by default; but it is (by default) subject to being overridden by shutter-button focus. You may think you've gotten the subject in focus via the back button; but when you press the shutter botton, the camera may have a different idea."

I have yet to set it enabled, by default, on a camera body.  Reseting custom controls disables it..  The metering system is enabled by default, but not metering and focusing.

---

From page 44 of the June 2016 edition of the 5D Mark III instruction manual:

"In the P/Tv/Av/M/B modes, pressing the <AF-ON> button will execute the same operation as pressing the shutter button halfway."

This is confirmed on pages 70, 201, and 228.

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Guess what. That’s not BBF.  If the shutter and the button do the same thing, that’s not BBF.  With BBF, pressing the shutter halfway only activates the metering, but not AF.  Not activating AF when you press the shutter is the whole point.  

I find it useful in One Shot mode, such as focusing on a bird among tree branches.  I can focus, and then press the shutter without the camera refocusing.

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Er ... no. If you use a back button (by default, <AF-ON>) to achieve focus, that's back-button focus. Many users define idiosyncratic versions of BBF, using the camera's button assignment capability; and some of those defeat the shutter button's AF capability as you indicate. But they're all forms of BBF. You get to choose how BBF works on your cameras, but you don't get to impose an unnecessarily narrow definition of the term.

[Waddizzle]

Whatever, Bob.  BBF mode means the shutter does not activate AF.  That’s the whole point.  You must another button to AF.

There are lots of articles out there that tell you how to setup BBF on your camera.  All of them tell you to disable the AF on the shutter button.

[ebiggs1]

Bob
Boston, Massachusetts USA

Glad it's you and not me!