# D7000, 85mm 1.8D, backfocus problem?



## flea77 (Jan 23, 2011)

I recently bought a 85mm 1.8D and use it on a new D7000. I noticed that I kept missing focus in sports so I went from 1.8 to 2.2 and that seems to help. Yesterday I decided to play around a bit and messed with the focus adjust on the camera. I noticed I got pretty sharp pictures at -20 which is the max. At this point I need to run more tests to see if it is just that lens or the body.

My question is this. Is it possible for the body to actually have the focus problem and not the lens? Those of you who have bodies with focus adjust, it is normal to have to adjust certain lenses?

What is the best way to determine which lenses, or if my body has the problems?

Thanks,

Allan


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## D-B-J (Jan 23, 2011)

My only guess would be to set an object 5 feet away from the focal plane of the camera, and set the lens to exactly 5ft(on the focus scale).  Then take a pic and see what happens?

hopefully someone with a little more knowledge on backfocus can help.

Regards,
Jake


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## Dao (Jan 23, 2011)

This site contain information about how to test the focus.

Nikon D70 Focus Chart

I will try the test with different lenses and see.  It should give you a better idea on if the it is a body issue or a particular lens issue.


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## KmH (Jan 23, 2011)

First - few fast lenses focus sharply wide open.

Second - 2.2 is only 2/3 of a stop from 1.8. It's usually recommended a lens be stop down at least 2 stops (3.5 in your case) to get sharp focus.

You could check out this web site: Home


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## flea77 (Jan 23, 2011)

KmH said:


> First - few fast lenses focus sharply wide open.
> 
> Second - 2.2 is only 2/3 of a stop from 1.8. It's usually recommended a lens be stop down at least 2 stops (3.5 in your case) to get sharp focus.


 
True, few lenses are very sharp wide open, although if you can manually adjust the focus and get the image sharper than the camera does on autofocus, the problem is not with the overall sharpness of the lens.

In this case the lens at 1.8 or even 2.2 is obviously out of focus, not just soft. Areas behind the subject are obviously in focus, and are plenty sharp enough.



KmH said:


> You could check out this web site: Home


 
Yep, you and Dao both linked to the same info, thanks. Don't know why it did not show up in my searches, my googlefu must be asleep, thank!

Allan


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## flea77 (Jan 23, 2011)

OK, quick and dirty test done, here is the report:

I took all my lenses and tested them on the chart. Although a protractor was not used, I did attempt to maintain somewhere near 45 degrees. IMO the angle is really only useful for determining how OOF it is in one direction or the other and will not affect the test.

One lens, the 85, needed -20 correction. One other required -10 but is always shot at long range so I am not worried about it since the depth of field increases exponentially with distance. One other required -2 which was very hard to judge. The rest required no adjustment.

The 85 is sharp at -20 right where it is supposed to be. Since this essentially "fixes" the issue I would not worry with it except for two things. 1) It is at the limit. If it shifts any more I will not be able to correct it. and 2) The lens is new from an authorised Nikon USA dealer. Now I just need to contact them and see what I need to do to get an exchange.

Thanks for your help!

Allan


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## djacobox372 (Jan 23, 2011)

Focus can vary a tad from lens to lens, and it's especially important on very fast lenses like the 1.8.  

That's why that focus adjust feature is there--it sounds like it fixed your problem, so don't worry about it.


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