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08-09-2012, 07:17 AM   #1
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Front / Back Focus Tuning

I know there are lots of different ways of calibrating your lenses to your K5, but thought I'd share the technique that I just found & used successfully. My wife has a bunch of paintings that her mother had painted prior to her death a couple of years ago. She wanted some pictures taken of some of them, as she's sending them out to relatives. The only lens that I've really had front / back focusing issues with has been my Tamron 17-50 2.8. I've tried different tuning techniques, but always got varied results. For my setup, I needed this focal length, as it was best suited for most of the paintings. Of course the first couple of shots revealed that they were not that sharp. My mind started thinking, and this is what I ended up doing. I first took a controlled shot of the first painting using Live View, and this shot was dead sharp. Next shot was without live view, and as expected, was not as sharp as it was with LV. Just as a note, camera was on a tripod pointing straight down on the painting. (on the floor) I went into the fine tuning for the focus, and after a few go's at it, got it adjusted to be as sharp as the LV. The nice thing with using a painting vs just using some regular printed item is that you can see all the texture of the paint as well as the texture of the canvas, so this just make it so easy without having to guess if it was close or not. I've been struggling with this lens and getting it to where I want it, but now I expect I should be happy with the results.

08-09-2012, 07:35 AM   #2
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Thank you for sharing by your technic.
Here it is my trial with SMC Pentax 50mm 1/1.7 at F/1.7 no tripod...
The painting was on the wall...natural light...
08-09-2012, 07:43 AM   #3
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I shot my iphone until the home button was sharp and there was minimal CA where the black screen meets the white body
08-09-2012, 07:58 AM   #4
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QuoteOriginally posted by eccs19 Quote
front / back focusing issues with has been my Tamron 17-50 2.8.
Have in mind that you have adjusted only for one focal length.

After multiple testing procedures, my Tamron 17-50 was perfect at 50mm with -5 adjustment but needed +8 at 17mm so if I adjusted at 50mm with -5 it was +13 off at 17mm.

It is now in for service and calibration.

Seems there are lots of focusing issues with this lens.

08-09-2012, 08:12 AM   #5
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Original Poster
QuoteOriginally posted by Patajac Quote
Have in mind that you have adjusted only for one focal length.

After multiple testing procedures, my Tamron 17-50 was perfect at 50mm with -5 adjustment but needed +8 at 17mm so if I adjusted at 50mm with -5 it was +13 off at 17mm.

It is now in for service and calibration.

Seems there are lots of focusing issues with this lens.
Actually, I did it at a few different focal lengths, as there were different sized paintings. Mind you, they were probably all between 35mm and 50mm. Nothing on the short end. It is a good point, and I do agree about there being focusing issues generally with this lens. I think it's one of the more problematic lenses I've seen reported. Now I'm going to have to set it up again and try it at the wide end. Thanks. (not sure if that's a good thanks or sarcastic thanks.)

Also as a note, I've got it at -5 as well.
08-09-2012, 08:43 AM   #6
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After reading Patajac's info, I tested again. From about 35 to 50mm, -5 seems to work well. Once it gets to around (i tested at 28mm), it starts to go. I have to bring it back to around 0 to be accurate. Funny thing is that I then went to 17mm, and it started going back into the negative. About -2 to -3 seemed best. Definitely not as bad as Patajac's, but it does vary for sure.
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