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11-19-2010, 08:35 PM   #1
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Is my K-7 body causing back focusing??? what shall I do?

Hi guys!

1 month ago, I found that my *16--50 back focuses at f/2.8 between 45--50mm on my k-7 body. I thought it was the problem of the lens, so I sent the lens to AZ for repair.

1 week ago, I bought a *50--135, which still back focuses throughout the focal range... Now I suspect the symptom may be caused by the body. So I found another k-7 body and put the *50135 lens on, the result is: the lens is still a little bit back-focusing, but much less severe than on my body.

OK, so based on these facts, can I say that my body causes all the focusing problems? Or it still might be a body-lens-joint-effect? I already have the replacement *50135 on the way, but I am not confident at all that it will perfectly match my k-7 body...

thanks a lot for all the inputs!

11-20-2010, 05:20 AM   #2
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Look in the manual on how to fine adjust focus. (I cannot remember the menu item off hand)
You can make a global adjust, or fine tune each lens.
Better to try that on your own than do without camera and lens for several weeks.

You will want to get a focus test chart, (http://focustestchart.com/chart.html)
Follow directions closely and make sure the problem is actually a back/front focusing issue.
11-20-2010, 09:20 AM   #3
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QuoteOriginally posted by amoringello Quote
Look in the manual on how to fine adjust focus. (I cannot remember the menu item off hand)
You can make a global adjust, or fine tune each lens.
Better to try that on your own than do without camera and lens for several weeks.

You will want to get a focus test chart, (Nikon D70 Focus Chart)
Follow directions closely and make sure the problem is actually a back/front focusing issue.

+1, and read the rest of the manual while you are at it.
11-20-2010, 11:52 AM   #4
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Original Poster
thanks guys!

I did try to use the in body focus adjustment, the only concern is that it is a zoom... and it only severely back focuses at the 50mm end, so if I adjust it to, let's say, +10, then it will cause the 135mm end to front-focus...

11-20-2010, 01:43 PM   #5
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QuoteOriginally posted by shang Quote
I did try to use the in body focus adjustment, the only concern is that it is a zoom... and it only severely back focuses at the 50mm end, so if I adjust it to, let's say, +10, then it will cause the 135mm end to front-focus...
Depending on what your focus distance and f-stop was when you tested at 50mm, almost 2/3 of your in-focus depth of field would be behind the point of focus. A common mis-conception is that it should be 50-50. At the long end you would expect the split to be almost 50-50, but still favoring a depth behind the actual focus point.
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