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02-09-2011, 02:36 PM   #1
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K-5 AF fine adjustment - does it work for non Pentax lenses?

Hi

I have been trying to calibrate my lens collection to my new K-5 with the Spyder Lenscal.

The process worked on all my Pentax lenses (DA21, FA24, FA43, DA70, FA-J 18-105, DA 18-35) but inexplicably does not seem to yield any difference on my Sigma 18-50 EX.

I still haven't finished calibrating my Pentax 100-300 and Tamron 28-300 yet. It started raining on me and I had to stop calibrating.

Has anyone successfully calibrated the K-5 to a non Pentax lens? I know there are issues with using SR on non Pentax lenses but I didn't think AF adjustment would be a problem (manual doesn't mention any limitation).

PS - my K-5 seems to have a tendency towards back focusing. Maybe this is the reason I don't have FF in low light?

02-09-2011, 02:39 PM   #2
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Yes, my Tamron 17-50/2.8 calibrated nicely.
02-09-2011, 02:52 PM   #3
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sigma lenses don't have a lens ID. emailed sigma about this and that was their reply.

it will or should work, but if you put another sigma lens, the k5 will think it's the same lens that you calibrated and will apply the lens AF offset.

i had that same issue with my sigma 17-70 and 50-150.
02-09-2011, 02:53 PM   #4
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Yes and no, quit a few sigma lenses share the same id-number so two (or more) entirely different lenses get the same adjustment as the camera can not tell them apart. I have for instance a sigma 10-20 and a sigma 17-70 and they can not be adjusted separately.

Edit, to slow...

02-09-2011, 03:01 PM   #5
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Thanks for the fast response, guys.

Yes, you are absolutely right - the Sigma 18-50 EX does not have a lens ID - Lightroom shows it as "Unknown Sigma lens" so guess that's the problem.

I'll try adjusting my Tamron and see if it works on the Tamron.
02-09-2011, 03:21 PM   #6
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QuoteOriginally posted by Christine Tham Quote
...
PS - my K-5 seems to have a tendency towards back focusing. Maybe this is the reason I don't have FF in low light?
The fuss has been about FF in low/tungsten light relative to daylight: AF works great in daylight but there is FF in low/tungsten light. Hence, if you have BF in daylight, you might very well be just fine in low/tungsten light.

As for the manual and 3rd party lenses I suppose Pentax kind of pretends that there is no such thing. I guess it is really about them not wanting to make claims of them working or not, which is reasonable: they cannot take responsibility of products from other manufacturers, but probably don't want to chase them off around the brand either.
02-09-2011, 03:47 PM   #7
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QuoteOriginally posted by opiedog Quote
sigma lenses don't have a lens ID. emailed sigma about this and that was their reply.
If they told you that, they don't know what they're talking about... Sigma lenses most definitely have an ID. You can use Exiftool or another Exif viewer to verify this.

QuoteQuote:
it will or should work, but if you put another sigma lens, the k5 will think it's the same lens that you calibrated and will apply the lens AF offset.
That's true for *some* Sigma lenses, not all of them.

QuoteQuote:
i had that same issue with my sigma 17-70 and 50-150.
Strange. I have both of these lenses, and my K-7 tells them apart and I can use a different AF adjustment values for each one.
02-10-2011, 11:18 AM   #8
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QuoteOriginally posted by jolepp Quote
The fuss has been about FF in low/tungsten light relative to daylight: AF works great in daylight but there is FF in low/tungsten light. Hence, if you have BF in daylight, you might very well be just fine in low/tungsten light.
Just to clarify.

There is actually no BF on the factory AF adjustment. All shots taken on all lenses are correctly focused.

It's just that the "focus zone" appears to be slightly shifted towards the back - ie. it extends less in front of the target focus point and more to the back of the focus point.

Does that make sense?

I have been trying to adjust the lens so that the focus zone extends equally to the front and the back.

Am I doing the right thing? Should I just have left the camera at factory setting?

I am tempted, given the camera will not adjust AF for my Sigma lens, to reset everything back to factory.

02-11-2011, 06:09 AM   #9
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QuoteOriginally posted by Christine Tham Quote
...
It's just that the "focus zone" appears to be slightly shifted towards the back - ie. it extends less in front of the target focus point and more to the back of the focus point.
...
AFAIK it is supposed to be like that in general, however, with small target distances it gets closer to being equally thick on both sides of the plane of 'absolutely correct' focus (which is infinitely thin). At any rate I'm having a similar experience with my Tamron 17-50 1:2.8: at -10 it might benefit from an additional click of two to be spot on in daylight; it used to be just fine with the k-x (currently in warranty repair) even in tungsten light so I'm annoyed, but this in itself is hardly Pentax's fault and might get better (or worse) in case my K-5 gets replaced for its sensor stains (I'm holding sending it in for now to maybe avoid another service round-trip delay and/or the camera sitting on a shelf of the repair shop while they are waiting the word from Pentax as to what to do about the AF / tungsten/low light FF).

Last edited by jolepp; 02-11-2011 at 07:56 AM.
02-11-2011, 11:37 AM   #10
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QuoteOriginally posted by jolepp Quote
AFAIK it is supposed to be like that in general, however, with small target distances it gets closer to being equally thick on both sides of the plane of 'absolutely correct' focus (which is infinitely thin). At any rate I'm having a similar experience with my Tamron 17-50 1:2.8: at -10 it might benefit from an additional click of two to be spot on in daylight; it used to be just fine with the k-x (currently in warranty repair) even in tungsten light so I'm annoyed, but this in itself is hardly Pentax's fault and might get better (or worse) in case my K-5 gets replaced for its sensor stains (I'm holding sending it in for now to maybe avoid another service round-trip delay and/or the camera sitting on a shelf of the repair shop while they are waiting the word from Pentax as to what to do about the AF / tungsten/low light FF).
two weeks ago it was rumoured there was going to be a firm ware fix in two weeks.

I'm sitting here tapping my fingers on the table and periodically refreshing ...

Latest K-5 Firmware Update : Software Downloads : PENTAX
02-11-2011, 11:38 AM   #11
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Thanks - I think I might reset my AF adjustment back to factory. To paraphrase the manual, don't adjust unless you know what you are doing. And it appears I don't.
02-11-2011, 11:45 AM   #12
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QuoteOriginally posted by Christine Tham Quote
Thanks - I think I might reset my AF adjustment back to factory. To paraphrase the manual, don't adjust unless you know what you are doing. And it appears I don't.
Download this pdf and print out page 18

http://focustestchart.com/focus21.pdf

it's a great focus test chart, and will show you the amount of FF or BF. much more accurate than 3 batteries. Shoot it at an angle of 45 degrees about 3 or 4 feet away. focus on the centre line. http://focustestchart.com/chart.html


Calibrating your lenses is EASY using this.
02-11-2011, 12:07 PM   #13
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QuoteOriginally posted by Christine Tham Quote
It's just that the "focus zone" appears to be slightly shifted towards the back - ie. it extends less in front of the target focus point and more to the back of the focus point.

Does that make sense?
Nothing to be worried about. It is just the laws of physics and perfectly ok; I'm pretty sure it has been like this since the beginning of photografic history
Just look at the DOF marks on many old manual lenses.
The factory settings seems to be just fine.
02-11-2011, 04:27 PM   #14
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QuoteOriginally posted by Smeggypants Quote
two weeks ago it was rumoured there was going to be a firm ware fix in two weeks.

I'm sitting here tapping my fingers on the table and periodically refreshing ...

Latest K-5 Firmware Update : Software Downloads : PENTAX

at least your be able to tell the rest of us if a new FW does hit the download area
02-11-2011, 04:49 PM   #15
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QuoteOriginally posted by Christine Tham Quote
Thanks - I think I might reset my AF adjustment back to factory. To paraphrase the manual, don't adjust unless you know what you are doing. And it appears I don't.
at 50mm F2.8 , distance to image 50 cm, the DOF is 1.02 cm, the near limit is 49.5 cm and the far limit is 50.5 cm......... that's a equal amount of DOF in-front and behind the subject......


if however the subject is 1000 cm away...the dof will extend further to the rear of the subject than the front...in this case ...DOF is 474 cm, near limit is 816 cm, far limit is 1291 cm........so that's 184 cm in front of the subject and 291 cm behind the subject .


so if shooting focus charts at very close distances you should be aiming for equal DOF, in front and behind the subject.......as the 1/3-2/3 rule is only at much greater distances from the focal plane
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