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When I shoot with my camera with many lenses at relatively wide apertures, and try to focus to infinity, (manually, using zoomed live view or otherwise), I find that end result pictures are not focused at infinity. Actually, it can be hard to tell what it is focused at, but I've not been able to obtain focus at the very distant subjects.

I have trouble understanding whether I simply have bad technique, or if the camera body has a flaw. The flaw which I am specifically thinking of is that the lens mount is actually slightly too far ahead of the sensor (or the sensor is mounted too deep). The problem is, through very limited testing, I've noticed this problem with some other cameras (all cheap crops mind).

Can I verify the problem reliably, without sending the camera off to a service centre (warranty issues, cost, etc etc)?

EDIT (for camera and lens info): Camera: EOS 650D Lenses tested: Canon EF 50mm f1.4, Canon EF-S 18-55 f3.5-5.6 IS II

UPDATE: I attach some pictures taken with my cellphone camera to illustrate how the final image is WORSE than the live view result. These were taken using a fully manual lens, wide open @ F/2.8.

Manually focused in live view with 10x magnification - cellphone picture of camera LCD

Resulting exposure - cellphone image of camera LCD Resulting exposure - actual image crop developed from RAW Resulting exposure - actual image crop from embedded JPG preview

  • Just to check: you're not expecting the lens to be at infinity when it is at the limit of the focus ring, right? – mattdm Sep 11 '14 at 23:29
  • Correct, I'm aware of the capability of modern autofocus lenses to focus past infinity, although I do have 1 old hard-stop at infinity lens. – user1207217 Sep 11 '14 at 23:31
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    Could you tell us what camera and what lenses? – JenSCDC Sep 12 '14 at 0:03
  • @AndyBlankertz I was trying to keep the question away from specific equipment, but I have updated the question to reflect the main equipment I use that I have trouble with. – user1207217 Sep 12 '14 at 10:46
  • Have you tried something like focusing on the edge of a building (very easy to focus on)? Is the problem just with AF or do you have the same problem with MF? – JenSCDC Sep 12 '14 at 11:06
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I think there's a couple of things going on here. Firstly some lenses exhibit focus shift, whereby the plane of sharpest focus moves as the lens is stopped down (this is usually due to residual spherical aberrations).

Secondly camera live view feeds are subject to certain restrictions in the area that can be read from the sensor in real time, and will sometimes interpolate the image at certain magnification settings. The upshot is the live view image is often less sharp than it should be.

Live view typically works with the lens wide open. So it may be the case that the live-view looks out of focus simply because the lens is soft wide open (the 50 f/1.4 definitely is) and the live view feed is softer than it should be. When you take an image you get focus shift and so the final image is also soft.

I would suggest you focus stopped down (there should be an option for this somewhere) and take an image to see if that fixes the problem.

  • It is my bad for not saying so, and I appreciate what you are saying, but the examples given above were taken using a fully manual lens - manual aperture, manual focus, and what you see should be what you get, or am I incorrect in believing so? In this case the lens was wide open, F/2.8. – user1207217 Oct 9 '14 at 12:22
  • I did also do a test with the 50mm using the DOF preview button to focus, but it was a bit harder to tell with the moon as a subject. I will go and make some more sample photos (of course, I have to use my cellphone to take the picture of the live view) – user1207217 Oct 9 '14 at 12:25
  • @user1207217 If the lens is indeed fully manual then what you see in live view should be pretty much what you get. In any case the final resulting image should be sharper than the live view image. I cannot think of any reason for it to be the other way round, unless shutter speed was a factor (the image you posted shows no signs of motion blur). How was the second image obtained? Was it a cell phone picture of the camera's LCD screen or did you download the image from the camera's memory card? – Matt Grum Oct 9 '14 at 12:51
  • They're both cellphone pictures of the resulting image viewed on the cameras LCD - just to remove the variability. I'll post the actual image taken later tonight. – user1207217 Oct 9 '14 at 12:59
  • Well, it turns out it's a problem with the cameras JPG processing .. a bit of care in a RAW developer (pic 3) shows a decent image (no sharpening) but the embedded JPG preview (pic 4) is really duff. It seems the contrast of the camera LCD does not help perception of sharpness .. Time to try again with my auto lenses.. – user1207217 Oct 9 '14 at 20:11

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