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11-08-2011, 09:21 PM   #1
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DA 17-70mm backfocus with k20d

Interesting one for you.

Processing shots from a recent trip and noticed that some of the shots taken with the K20D & DA 17-70 combo had just missed the focus on what would have been stellar shots. As this was my wifes camera I initially just put it down to operator (we dont need to go into that) error.

But, as I have sifted through more I started noticing a pattern emerging and ran some tests.

What I have found is that this combo focus' perfectly from about 35mm through to 70mm, absolutely spot on.....but back focuses to hell from 17 -35mm

So....where to from here? anyone else had similar problems and did you find any solution?

Cheers
Grant

11-08-2011, 09:46 PM   #2
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Hmmm...more tests.
I have now adjusted the focus to +10...this has improved focus at the wide end without causing any problems at the zoom end. Still back focuses at 17mm but a lot less so and cuts into perfect around mid 20 mm mark.

Guess you gotta be thankful for small mercies.
Cheers
Grant
11-08-2011, 11:32 PM   #3
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I would thoroughly test the lens and try to get it replaced if it's still under warranty. Updated your thread title, BTW

Adam
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11-09-2011, 02:40 PM   #4
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Thanks Adam.
Unfortuneatley it is a long way out of warranty. To date the lens spent its life on the K200D with no noticeable issues....thats why it is all a little puzzling.
Cheers
Grant

11-09-2011, 03:50 PM   #5
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QuoteOriginally posted by Mallee Boy Quote
Thanks Adam.
Unfortuneatley it is a long way out of warranty. To date the lens spent its life on the K200D with no noticeable issues....thats why it is all a little puzzling.
Cheers
Grant
Read an interesting article some time ago about focusing issues (can't find it to link) which basically said there's no such thing as a back/front focussing lens it's the camera & lens combo that back/front focus. The reasoning was all manufactured items will have some variation due to the nature of the manufacturing process but will still be within the manufacturer's tolerances; so camera A might match well with a given lens but if camera B is at the other end of the manufacturer's tolerance you could get focusing issues with that same lens.
11-09-2011, 04:23 PM   #6
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Unfortunately, in the case of zoom lenses, one pretty much has to send the camera and lens to service so they can be calibrated to each other if things aren't working according to plan.
The other option is to shoot at a higher ISO and use the headroom that gives to shoot a smaller aperture, which will give more depth of field. Unfortunately, this is not a desirable outcome most of the time.
11-10-2011, 02:23 PM   #7
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Thanks gentlemen....sensor need a clean anyway so a service call is probably the smart option here.
Thanks for sharing your knowledge.
Grant
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