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Autofocus woes

davetong
Contributor

Canon D70, 85mm lens, 1/200 at f2.8

It's not sharp, even though the autofocus claims to have a good lock on. 

Judging by the tiles on the floor it's focused a good 1m too short.

Does the camera need servicing?

 

Also, what's with "the camera reports the distance as being between 2.88m and 11.9m" - that's a massive range given the 0.78m depth of field

 

Screen Shot 2019-02-27 at 5.41.43 PM.png


Original image at https://www.dropbox.com/s/agk1qtakqh9j4iz/_MG_6750.DNG?dl=0

18 REPLIES 18

Waddizzle
Legend

@davetong wrote:

Canon D70, 85mm lens, 1/200 at f2.8

It's not sharp, even though the autofocus claims to have a good lock on. 

Judging by the tiles on the floor it's focused a good 1m too short.

Does the camera need servicing?

 

Also, what's with "the camera reports the distance as being between 2.88m and 11.9m" - that's a massive range given the 0.78m depth of field

 


As far as the camera reporting a distance between 2.88mm and 11.9m, that is called DOF, or Depth of Field.  One explanation for the wide range of distance is that it is reporting the focusing range of all of the active AF points.  That is a fairly old LR add-in, so it could be reporting incorrectly with more recent releases of LR.  

 

[The report shows 31 AF points on a camera that only has 19 AF points.]

 

Judging from the number of active AF points, combined with the fact that you are in focusing/ in AI Focus mode, it seems likely that the camera dial was set to Green [A], Automatic, to take the photo.  Or, maybe not.  In either case, experienced users avoid AI Focus like the plague, because it does not always lock focus before firing the shutter.  Stick to P mode, and One Shot focusing mode.

BTW, when an entire photo is evenly OOF throughout the entire frame, that points to one of two causes.  One, the cause is camera motion blur, or even blur from a moving subject.  Two, the camera/lens combo might need a focus calibration.

However, there is also a third more probable cause, IMHO.  It is the lens.  The EF 85mm f/1.8 USM does not focus very consistently.  It does not focus consistently enough to make bothering with an AFMA adjustment worth the time.  

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"The right mouse button is your friend."

Thanks for the response.

The shot isn't OOF throughout the frame; as I noted, some of the tiles in front of the subject are in focus, which would

appear to rule out camera shake, rather it indicates to me that the camera had misjudged the distance by approx 1m. 


I'm not convinced that it's the lens; I've experienced similar problems when shooting with the 50mm 1.8 at low stops
I haven't had problems with the kit zoom lenses, but that's not surprising since they don't go wide enough
to create a shallow enough depth of field. Some other shots were pin sharp, which tends to rule out focus calibration.
If there is a problem it's either with the camera or the operator.


The shot was taken in manual mode, not automatic. I used to use AI Servo mode; I switched to AI Focus

because of the visual indication of focus lock (hollow laugh) - I'll try switching to One Shot and see if that helps.

I've never fully understood why, but Canon claims that the D70 has "up to 31 AF points" in Live View.
https://support.usa.canon.com/kb/index?page=content&id=ART142752
I wasn't shooting in Live mode so it's irrelevent, but I expect that's why the plugin reports the number.

Regarding depth of field, the plugin explicitly reports that as 7.02-7.80m, which is what I'd expect when shooting at f2.8

so that doesn't explain why the EXIF data reports the distance to the subject as being between 2.88m and 11.9m

Stop using AI-focus mode and you will be fine.

EB
EOS 1DX and 1D Mk IV and several lenses!

"...some of the tiles in front of the subject are in focus..."

 

I don't think so. They have more contrast but still look OOF to me.

EB
EOS 1DX and 1D Mk IV and several lenses!

Here's a better example:

https://www.dropbox.com/s/ius8xoh48ntrzv0/_MG_7079.DNG?dl=0

 

This was taken in Manual mode, using One-Shot focus. Same body and lens.

The leaves and the tree in the upper left and the gravestones on the right are sharp,

but the focus locks are supposed to be on the crypt in the distance.

 

I'm going to try cleaning the AF sensors

 

Screen Shot 2019-03-01 at 10.21.00 AM.png


@davetong wrote:

Here's a better example:

https://www.dropbox.com/s/ius8xoh48ntrzv0/_MG_7079.DNG?dl=0

 

This was taken in Manual mode, using One-Shot focus. Same body and lens.

The leaves and the tree in the upper left and the gravestones on the right are sharp,

but the focus locks are supposed to be on the crypt in the distance.

 

I'm going to try cleaning the AF sensors

 

Screen Shot 2019-03-01 at 10.21.00 AM.png


I suggest using just the center AF point when using One Shot mode.  The center AF point is the most sensitive and accurate Af point in that camera.  I also suggest looking at the AF points in Canon’s DPP software, just as a benchmark comparison.  DPP can only show you the active AF points,   

 

I will also suggest trying a different lens.  I am not the world’s greatest fan of that lens.  My copy does not seem to focus consistently at f/2.8 and wider.  

 

Are you using any lens filters?  If so, remove it.  I have also noticed that CPL filters can seem to confuse phase detection AF systems.  UV filters tend to be unnecessary because most digital sensors have UV built into the image sensor assembly.

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"The right mouse button is your friend."

Here is the full, uncropped screenshot. And as I said before, the full, raw image is on Dropbox:

https://www.dropbox.com/s/ius8xoh48ntrzv0/_MG_7079.DNG?dl=0

I recently purchased this 85mm f1.8 lens as a portrait lens. Unfortunately I don't currently have the budget

for the high-end lenses, and the kit 18-50 and 55-250 lenses don't seem to show the problem, probably because they are so slow.


I have had similar issues with the 50mm f1.8 lens. 

The frustrating thing is that while it's not consistent I do find that several of the photos in a particular set will show the problem.

 

 

Screen Shot 2019-03-01 at 4.40.23 PM.png

I suggest using just the center AF point when using One Shot mode.  The center AF point is the most sensitive and accurate Af point in that camera.  I also suggest looking at the AF points in Canon’s DPP software, just as a benchmark comparison.  DPP can only show you the active AF points,   

 

I will also suggest trying a different lens.  I am not the world’s greatest fan of that lens.  My copy does not seem to focus consistently at f/2.8 and wider.  

 

Are you using any lens filters?  If so, remove it.  I have also noticed that CPL filters can seem to confuse phase detection AF systems.  UV filters tend to be unnecessary because most digital sensors have UV built into the image sensor assembly.”

 

——————————————————

 

Try the above, and get back to us.

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"The right mouse button is your friend."

"The frustrating thing is that while it's not consistent I do find that several of the photos in a particular set will show the problem."

 

David, 

I think you gear is working properly. I don't think you understand how it works, though. The camera will always try to put the closest thing in critical focus. The rest may exceed your DOF. If I read your EXIF correctly you shot at f2.5 using an 85mil..  Pretty small DOF at that aperture.  Do this for me, turn off all the focus points except the center one. Use only the center point.  Use One-shot. Put the camera in P mode. Take the very same photo if you can and focus precisely on what you want on sharp focus.  I bet it will be fine.

 

DO NOT TRY TO CLEAN ANYTHING INSIDE THE MIRRORBOX OF YOUR CAMERA. Put nothing smaller than a football in there.

 

Tip: If you want more of the shot in focus try a smaller aperture like f11 or f16. Your SS was way too fast for a shot like this. It isn't necessary.

EB
EOS 1DX and 1D Mk IV and several lenses!
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