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Old Jan 23, 2007, 9:03 PM   #1
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I have a Minolta 5D and a Tamron 28-105mm 2.8 lens, when using the auto-focus the images are not clear. Is there a setting or way to calibrate the lens?

Thanks stoltzy
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Old Jan 23, 2007, 11:12 PM   #2
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I am not familiar with the Minolta 5D, but have had AF problems with various other cameras.

Most dSLR cameras today have multiple AF points, so the problem may be which AF point the camera is using, versus the AF point you think the camera is or should be using.

If you can set your camera to use only one AF point do so, and then try some focus tests to see if that solves your AF problem.

Another question: is this focus problem only with this one lens, or do you have similar problems with other lenses?
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Old Jan 23, 2007, 11:22 PM   #3
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No, this is the only lens I have this problem with. I have tried spot AF focus and Wide AF focus but nothing seems to help
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Old Jan 24, 2007, 7:43 AM   #4
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It may not be Autofocus (that lens is relatively soft wide open according to MTF Charts). So, that may be why the photos are not "clear" (if you're trying to shoot with wider apertures).

I've got the older Tamron 35-105mm f/2.8 (which is about as sharp wide open at f/2.8 as the newer 28-105mm is stopped down to f/4). But, even the older version is not the sharpest lens at wide open apertures (even though it tests much sharper than the newer 28-105mm 2.8 ).

Have you got a 50mm? I'd check the camera body using it to see if you have a camera issue. You may have a problem that isn't obvious with other lenses (you may be shooting at smaller apertures with them, so you'd have greater depth of field).

One way to check them real quick is to stagger some boxes, books, CD/DVD Cases, or similar items on a table.

Then, shoot the middle item and see if the ones just in front of it and just behind it are softer.

For example, this is a quick test I did using a 100m f/2 with my 5D using a few of my wife's books, focusing on the book in the middle.

If the book in front my focus point would have been sharper, the camera would have been front focusing. If the book behind it would have been sharper, it would have been back focusing. It looks close enough to me (especially since light was low).

Full Size Image:


You'll also find a ruler like chart that you can print in this thread (shoot at a 45 degree angle to it to check for focus errors).


If you have a focus issue, Sony/Precision can calibrate the body (a 50mm f/1.7 is used for AF calibration) If a 50mm tests good and you are seeing backfocus or front focus (not just soft images at wide open apertures) with the Tamron, then you may have a lens issue.

Some users have also calibrated the body themselves (via some hex screws that impact AF sensor alignment under the plate at the camera's tripod mount). But, you're better off letting Sony do it *if* you have a body versus lens issue.

If the Tamron tests good (no front or back focus issues), then the problem is likely that you're using it wide open (the photos may not be as sharp as desired at f/2.8 with it).

It could also be a technique issue (for example, you're trying to focus on someone's body versus their eyes at wider apertures where DOF is very shallow).

If the camera is good (testing it with a 50mm for front or back focus), and the Tamron lens is bad (front or back focusing), then I'd probably send it back to Tamron and let them check it out.

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Old Jan 24, 2007, 8:59 AM   #5
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Hi Stoltzy,

When you make a print on paper is it in focus?


Is it just out of focus on your camera screen?

If the focus is out on your screen but the print is in focus you should check the viewfinder focus adjuster (DIOPTER) before anything else.

Information is in your camera manual about doing this.

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Old Jan 24, 2007, 9:51 AM   #6
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Ronnie thought of what I was going to suggest.
I bump the dipoter on my DSLR on occasion and have to fix it.

If the camera confirms that focus has been achieved (for example a beep or a symbol in the view finder) and its still looks out of focus then it is probably the diopter.

The diopter is a correction that can be made to the eye piece for people with vision problems. It lets them look through the camera without having to wear their glasses.

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