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05-11-2013, 06:36 PM   #1
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K-30 + Tamron 28-75, focus seems off

Something seems to be off with either my K-30 or the Tamron 28-75, or maybe my standards are too high It's probably one of the latter two but I want to ask the wiser minds. I've been using it a lot on my K-30 since I got the K-30 last week. The first day, I took a lot of off-camera-flash pics, which mostly required apertures of 5.6+, so I didn't really notice any focusing issues. However, in natural light with lower aperture values, either the lens, body, or lens+body produce some very soft images.

The image below is at f/4.0, speed 1/125, ISO 100, 75 mm. Center point AF. Distance approximately 6-8 feet. Time was noon on an overcast day, New York time. Lighting was about as you see in the pic. It seems a bit fuzzy, especially when you look at the hair. Possibly some front focusing? The area around her right hand seems like it might be slightly more in-focus than the rest.



This one was at f/4.0, speed 1/125, ISO 100, 75 mm. Center point AF. Distance approximately 4 feet, time was 6:11 PM New York Time. While the upper picture wasn't so bad, this one seems worse. It's a pretty close crop and I focused on the fungus blob. Perhaps some front focusing again, near the bottom left corner of the pic?


I've tried some focus adjustment in the K-30 but the focused subjects still seem to come out blurry from time to time. But then sometimes it also nails the focus spot on. Please help!

PS - approximately how much would it cost to have the lens serviced? I bought it used so no warranty, if it would even apply in this case.


Last edited by ChooseAName; 05-11-2013 at 06:47 PM.
05-11-2013, 07:18 PM   #2
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The first one looks more like motion blur to me.
05-12-2013, 04:48 AM   #3
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Do an autofocus test-
Using Moire' Interference Patterns to Test DSLR Auto Focus

It is fast and easy for testing. But if this test determines autofocus is off, I suggest the tool here to adjust it-
PENTAX DSLRs: Front or Back Focusing Problems? Free test (Lens Alignment) charts for Pentax, Nikon, Canon, Sony, Olympus.
05-13-2013, 06:54 AM   #4
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i have a love hate relationship with this lens.

on my K10 and K5 I like the results, also with my K7 and flash, but with the K7 and natural lighting, or on my *istD, i find the results never seem to nail the focus. in fact,on the *istD i can actually see it do the first focus, and it is sharp in the VF and then on the fine adjust it goes a little off.

SOme of this, I am sure is relitive to the activity of the SR, some of it is related to getting the ideal aperture, F4 could be part of the problem.

For the OP

Note on the first shot, and i do not know if this is cropped or not, but there is nothing in the center AF zone. so exactly what was the focus target. To me, it would seem that the fabric of the stripe at her hip/hand is dead on

I do not know if you are dealing with an issue of front/back focus, or center vs edge sharpness.

05-13-2013, 12:44 PM   #5
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I experience the similar problem with my Tamron 17-50 F/2.8 on my k-30. This lens tends to front-focus at most of the focal length, especially at large apertures. I made a request for replacement but they haven't got back to me yet.
10-22-2013, 07:51 AM   #6
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Tamron 28-75 f2.8 has front/back focus issues. They almost all do. You'll have better results shooting with live view. You can use the AF microadjustment in the settings, but it will only do so much, and at least with my copy, it will never be perfect throughout the zoom range. If you adjust it so tele focus is spot on, wide focus will be off. Best you can do is aim for the middle. This is a known, common problem with the Tamron 28-75. I just leave it on my K-01 and don't worry about it

Charles.
06-07-2014, 02:07 PM   #7
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I have sent back two of these after testing them with my K3. Horrible back focus..
06-09-2014, 01:16 PM   #8
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That being said, Tamron did repair mine (at considerable cost), and it works flawlessly now. No more focusing issues at all.

Charles.

06-13-2014, 08:32 PM   #9
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Test the lens on a tripod, shooting flat objects perpendicular to the camera, like the ISO 12233 test chart or a newspaper page about 2 or 3 metres away, and:
- use bright light,
- stick to f2.8,
- use a fast shutter speed like 1/250 or more,
- set the ISO low (eg ISO 400 or lower),
- make sure the camera JPG settings are set to defaults,
- make sure no existing AF adjustments are active,
- use centre point AF.S
- remove any UV filter or other filter from the lens
then shoot the target using various focal lengths, review the results on a computer.
Just to make sure your testing technique is not at fault.

Then, if necessary, use the same test setup to make some progressive AF adjustments (+/-) until the target comes reliably in focus, or close enough at f2.8.

My Tamron 28-75 is a nice lens, but on the K-3 needs about -10 AF adjustment. However on the K-5 it needs none. And on the K-x it seems to have no problems.

However on the K-3 shooting at f4 or thereabouts usually makes any AF problems insignificant in real world use.
06-14-2014, 05:34 AM   #10
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QuoteOriginally posted by rawr Quote
Test the lens on a tripod, shooting flat objects perpendicular to the camera, like the ISO 12233 test chart or a newspaper page about 2 or 3 metres away, and:
- use bright light,
- stick to f2.8,
- use a fast shutter speed like 1/250 or more,
- set the ISO low (eg ISO 400 or lower),
- make sure the camera JPG settings are set to defaults,
- make sure no existing AF adjustments are active,
- use centre point AF.S
- remove any UV filter or other filter from the lens
then shoot the target using various focal lengths, review the results on a computer.
Just to make sure your testing technique is not at fault.

Then, if necessary, use the same test setup to make some progressive AF adjustments (+/-) until the target comes reliably in focus, or close enough at f2.8.

My Tamron 28-75 is a nice lens, but on the K-3 needs about -10 AF adjustment. However on the K-5 it needs none. And on the K-x it seems to have no problems.

However on the K-3 shooting at f4 or thereabouts usually makes any AF problems insignificant in real world use.
Thanks for sharing these very good instructions. About the only thing I might add would be to confirm focus using focus peaking in magnified live view. That would be done by acquiring focus using the PDAF system, switching off AF, switching to live view (focus peaking turned on) and long-press OK to magnify.


Steve
06-22-2014, 07:19 AM   #11
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QuoteOriginally posted by stevebrot Quote
Thanks for sharing these very good instructions. About the only thing I might add would be to confirm focus using focus peaking in magnified live view. That would be done by acquiring focus using the PDAF system, switching off AF, switching to live view (focus peaking turned on) and long-press OK to magnify.


Steve
sorry guys but the detailed instruction can not help this lens as it is completely out of boundaries. This might work to finetune with the in-camera settings but this lens is off the chart whatever you do.
07-09-2014, 06:04 AM   #12
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You never did come back and tell us whether it works in live view. If it exhibits the same issues in live view, it may very well be a bad lens. Front/back focus issues will not show up in CDAF/live view focusing mode.

Charles.
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