There has been some discussion of autofocus microadjustment here recently and I've also read many different articles on how to do it, by no means all in agreement. So I decided to try a very simple method myself and see how it went. These are the results so far, which I thought might be of interest.
After my reading around, I felt that one important factor was not given sufficient prominence in many accounts, but was in one. That is that you must first test the camera to see if it has an issue before you can make any conclusions about a lens. To do this you need at least two lenses.
I started with the 50D, an older model but which I bought used (low price, low shutter count) mainly to be permanently attached to my microscope, partly to avoid the hassle of attaching and reattaching one of the other bodies and also to avoid building up the shutter count on the pricier bodies when taking multiple images for stacking. This is, of course, all manual focus. However, I did take it out for a test run in the open, but the images didn't seem quite as sharp as I would expect. I thought it might have an a/f issue.
My testing method was very simple. I took a sheet of card and made a test target by gluing various things to it which had high levels of detail, a page of small print, an outdated foreign bank note etc. Then I simply set the aperture of each lens to wide open, used the centre a/f point and used an external flash, but with a/f assist disabled. I started with the 60 mm macro, a lens I know to be very sharp indeed. There was obviously a problem, target way out of focus. Dialling in +5 made it worse, -5 better, -10 better still, -15 no improvement, -13 perfect! Using -13 I then took a range of shots of other subjects, all at fully open aperture and all was fine. Then I tested the 85 mm F 1.8, exactly the same result, -13 needed. I then set “Same for all lenses” to -13 and used the 200 mm F2.8 L, perfect, disabled the microadjustment and all went out of focus again. The only logical conclusion is that the 50D itself has an issue that requires -13 adjustment. With only one lens, I wouldn't have known whether it was the lens or body at fault.
I then repeated the process with the 70D. Results here were completely different, all the lenses were spot on with no adjustment, in each case even a minor change +/- 2 made things worse.
I now have two pieces of information to use for further testing:
1. The 70D has no issues and so I can confidently use it to test other lenses, any problems can be attributed to the lens, not the camera
2. The three lenses I tested also have no issues, which is what I expected as they have all given very sharp results before, and so I can use them to test the other bodies
This is actually a very quick method once you are used to it. I'll test the rest of my lenses and bodies soon. I've tried one of the triangular folded things before, but without much success.
It's easy to automatically blame the lens in case of problems, but the body is equally likely to be at fault.
After my reading around, I felt that one important factor was not given sufficient prominence in many accounts, but was in one. That is that you must first test the camera to see if it has an issue before you can make any conclusions about a lens. To do this you need at least two lenses.
I started with the 50D, an older model but which I bought used (low price, low shutter count) mainly to be permanently attached to my microscope, partly to avoid the hassle of attaching and reattaching one of the other bodies and also to avoid building up the shutter count on the pricier bodies when taking multiple images for stacking. This is, of course, all manual focus. However, I did take it out for a test run in the open, but the images didn't seem quite as sharp as I would expect. I thought it might have an a/f issue.
My testing method was very simple. I took a sheet of card and made a test target by gluing various things to it which had high levels of detail, a page of small print, an outdated foreign bank note etc. Then I simply set the aperture of each lens to wide open, used the centre a/f point and used an external flash, but with a/f assist disabled. I started with the 60 mm macro, a lens I know to be very sharp indeed. There was obviously a problem, target way out of focus. Dialling in +5 made it worse, -5 better, -10 better still, -15 no improvement, -13 perfect! Using -13 I then took a range of shots of other subjects, all at fully open aperture and all was fine. Then I tested the 85 mm F 1.8, exactly the same result, -13 needed. I then set “Same for all lenses” to -13 and used the 200 mm F2.8 L, perfect, disabled the microadjustment and all went out of focus again. The only logical conclusion is that the 50D itself has an issue that requires -13 adjustment. With only one lens, I wouldn't have known whether it was the lens or body at fault.
I then repeated the process with the 70D. Results here were completely different, all the lenses were spot on with no adjustment, in each case even a minor change +/- 2 made things worse.
I now have two pieces of information to use for further testing:
1. The 70D has no issues and so I can confidently use it to test other lenses, any problems can be attributed to the lens, not the camera
2. The three lenses I tested also have no issues, which is what I expected as they have all given very sharp results before, and so I can use them to test the other bodies
This is actually a very quick method once you are used to it. I'll test the rest of my lenses and bodies soon. I've tried one of the triangular folded things before, but without much success.
It's easy to automatically blame the lens in case of problems, but the body is equally likely to be at fault.
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