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Old Apr 7, 2016, 3:44 PM   #1
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Default AF issues with Canon EOS Rebel SL1

I have had my Canon EOS Rebel SL1 for about 2.5 years, during which it's been used quite a bit (tens of thousands of photos). On a recent trip, I noticed that many of my photos shot on AF are blurry around the outside, particularly in the upper-left and lower-right corners. I took my camera to a repair shop in NYC yesterday and they said that if I shoot on manual I'll be able to get more focus points and therefore more of the photo will be in focus, but I'm just not buying this. I have never noticed this problem before, and the blurry areas aren't at a different depth as other in-focus areas of the photo. Please see the two attached images as an example and take note of the lower-left and upper-right corners; both images are unedited. Does anyone have any insight? Was the photo repair technician correct? Thank you in advance!
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Old Apr 7, 2016, 6:51 PM   #2
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It's easy to see that the upper right and lower left are not as sharp as the center. it's also easy to see that the lower right is sharper than the two other corners. distances are different, and the apertures might also introduce some DoF issues which could be the root cause.

I think it's far more likely that there's something wrong with your lens than with your camera, presuming that all the troublesome shots were taken with the same lens.

I suggest you try some more test shots where everything in all four corners is about the same distance from the camera, and look closely at the corners in those shots. I'd shoot straight on to a brick wall that filled the frame. Try it at different focal lengths with your zoom lens, and with different lenses if you have them. Try to capture the same focal length with multiple lenses if you can.
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Old Apr 8, 2016, 6:20 PM   #3
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Thanks for your response, TCav!

I took two photos of the exterior of my home. The first photo (more zoomed out) was taken with the kit lens (18-55mm). I usually use the kit lens and this is what was used to take the photos I previously posted. The second photo, which is more zoomed in, was taken using my 55-250mm lens.
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Old Apr 9, 2016, 7:15 AM   #4
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Given that the SL1 captures 5184x3456 images and the images you provided here are only 1024x683, there doesn't seem to be any problem with the focus over the entire frame.

If it were to have appeared, I'd have expected it at the wide end of the kit lens, since that's where it appeared in your original photos (one at 21mm and the other at 24mm).

At this point, I 'd say it looks like an anomaly with the circumstances of your original shots. The Canon 18-55 has sharp corners for a kit lens, so under normal circumstances, I wouldn't expect to have focus problems across the focal plane. Perhaps some combination of the extremely close objects, extremely distant objects, depth of field and hyperfocal distance all came together to produce those seeming focus errors.

It's also possible that there's a lens element that's loose and it's position varies, which causes an occasional misalignment resulting in the focus errors across the frame.

Have you noticed this in other photos you captured?
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Last edited by TCav; Apr 9, 2016 at 7:19 AM.
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