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06-01-2017, 10:50 PM   #1
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Tamron 17-50 Lens AF Fine Tune Question

My Tamron 17-50 F2.8 lens needs -10 AF adjustment @ 50mm on my K3 when used wide open.

Do I need to set it for every focal length or does the camera apply through out the zoom range?

Thanks.

06-01-2017, 10:55 PM   #2
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How do you know it needs -10? What test did you run to get that and how did you conduct such test? Also under what kind of lighting conditions?
06-01-2017, 11:03 PM   #3
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From what I have understood you should make the adjustment at the focal length you feel you will be using the most.

In my opinion this sucks. I mean the reason for buying a zoom lens at all focal length.

Now to highjack your thread

Like you, I have a tamron 28-75 that is front focusing on my K-30. I am yet to decide what to do.

To make things worse, which might be my own misunderstanding at this point, the focus points are sensitive compared to others.
For example the center focusing point is sensitive to about 2.8. The others less so. So does this mean that if you are shooting at f2.8 but using the top most focusing point, you could get at little out of focus shoots?

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06-01-2017, 11:07 PM   #4
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QuoteOriginally posted by Culture Quote
So does this mean that if you are shooting at f2.8 but using the top most focusing point, you could get at little out of focus shoots?
Well, yeah, they're rated to say, f5.6.

06-02-2017, 12:27 AM   #5
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QuoteOriginally posted by alamo5000 Quote
How do you know it needs -10? What test did you run to get that and how did you conduct such test? Also under what kind of lighting conditions?
Didn't do tests using a focus scale but general shooting and adjustments gives me comparatively sharp pics with -10 adjustment.

I noticed the same when I did tests with my K50 and focus scale, but didn't go with fine tuning.

Several of my recent shots turned out softer even tho the camera confirmed focus. Hence this fine tuning venture.

I will do some more testing using the scale and see how it behaves.

Yeah it's indoor lighting but used 540fgz flash to bounce of ceiling.
06-02-2017, 03:25 AM   #6
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Front and back focusing is common problem with K30 and various lenses. I have it on 17-50 and 100mm Marco WR with my K30. Focusing in live view is perfect, the problem persists only via the viewfinder. If you fine tune at 17mm you'll get good results, but at 50mm you stuck with front or back focus. If you fine tune at 50mm you'll... get the idea. So, what i did was... using live view...
06-02-2017, 04:40 AM   #7
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QuoteOriginally posted by Markovo Quote
Front and back focusing is common problem with K30 and various lenses..
I have never seen this statement anywhere on the forums.
06-02-2017, 05:50 AM   #8
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QuoteOriginally posted by Culture Quote
I have never seen this statement anywhere on the forums.
Well, I have seen it couple of times. Not sure that it was here or in other forums. But i sure have a problem with the two lenses i mentioned...

06-02-2017, 06:17 AM   #9
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QuoteOriginally posted by Markovo Quote
Well, I have seen it couple of times. Not sure that it was here or in other forums. But i sure have a problem with the two lenses i mentioned...
But it's a lens problem, not something specific to the K-30. The 17-50 often have front/back focus issues, with any cameras from all manufacturers.

QuoteOriginally posted by suraswami Quote
Do I need to set it for every focal length or does the camera apply through out the zoom range?
You can only set one adjustment per lens. Thus, you can only set it for one FL. But you should check all FL once the adjustment is done to be sure it didn't screw up focusing at other FL.

Fine adjusting zoom can often be a pain, since the perfect adjustment can vary depending on FL and focusing distance. these variations often make difficult, if not impossible, to perfectly calibrate the lens for all situation. From there, there are some strategies:

1) Calibrate for the worst case (usually longest FL, largest aperture, close focusing) and hope that things will be good enough in other conditions.

2) Calibrate for your most used FL, aperture, and focusing distance. But this means the lens migth be soft in extreme conditions.

3) Calibrate for good-for-all-but-not-perfect-for-anything. Usually done after step 1) or 2) if the results aren't acceptable for other FL than the one use for calibration. The adjustemnt is bring back a bit to get some kind of middle adjustment that is better than no adjustment, at all FL, but not as good as one specific to a FL when used at this FL, but still better at other FL.
06-02-2017, 07:00 AM   #10
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QuoteOriginally posted by suraswami Quote
Do I need to set it for every focal length or does the camera apply through out the zoom range?
You can only apply one adjustment per lens. This one adjustment is applied throughout the whole zoom range of a lens like the 17-50.

I'd test and adjust the AF based on the focal length you tend to use the most.

Note that on the Tamron, 17mm isn't likely to give you too many visible front/back focus issues since the depth of field is going to be very deep, even wide open. If there are any issues, you would be more likely to see them at 50mm. So I'd base any AF adjustments on the results of testing at 50mm.
06-04-2017, 07:46 PM   #11
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All the AF lenses I've checked on my new K-1 (diffraction patterns on monitor AND GhettoCAL self made target) were spot on.
Only my Tamron 2.8/70-200mm backfocuses so badly at the longest focal that even a +10 adjustment is not enough.
I didn't notice the problem in practice, cause I've used it on APS-C cameras in the past, and rarely fully extended.
On the K-1 the adjustment makes very little difference, if any.
Is there a way to make sure the correction is actually applied?
I have no other lens that needs adjustment, so I can't see if it's really going from one setting to the other, exchanging the lens.
Of course the general setting is left at zero, cause everything else works ok, including focus confirmation with MF lenses.
Any suggestion?

Cheers

P

07-07-2017, 11:23 AM   #12
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Even after -10 AF adjustment some of the photos are not sharp at F 2.8, depends on how much distance is my subject. Is there a way I can set my K3 to shoot from F3.2 on wards? I used the P mode to take pics at a family event, the camera sometimes went all the way to 2.8 even when there is enough light or ISO range and using an external mounted flash too.

The lens is very sharp from F3.2 and above.
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