[fwcetus]

I'm a mostly (as in 99%) very happy recent (last two months or so) owner of a K-3 (having upgraded from a K20D).

Most of my handful of AF lenses seem to work well with the K-3, although I did quickly apply AF Fine Adjustment settings to some lenses that did not focus very well).

However, I have more recently tried applying a corrective setting for a Tokina lens, and, while the setting, once made, does persist (in the sense that the K-3 "remembers" the setting), the setting itself seems to have absolutely zero effect on the actual focus plane when using the Tokina -- that is, the lens still back focuses by the same amount, regardless of what setting I (try to) apply to the lens in the K-3.

So, should the K-3 be able to change the "focus bias" of all the various and sundry third-party lenses? Or, does it require that the lens be of a recent design?, Or, must it be a Pentax lens only? Or...? ["Inquiring minds (at least this one) want to know."] Thanks for any feedback offered.

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Last edited by fwcetus; 08-17-2015 at 12:55 PM.

[stevebrot]

So, should the K-3 be able to change the "focus bias" of all the various and sundry third-party lenses?

Yes, as long as the lens properly supports the "data" contact on the mount to provide a lens id and other information. With your Tokina, there may be a little bit of a problem. The id code (3 23) is used by at least 4 different lenses (Pentax 100-300/4.5-5.6, Sigma 28-300/3.5-6.3 DL/DG, and your Tokina). The camera will "think" that it is talking to the Pentax 100-300.

Be aware that fine focus adjust is not the same as adjusting focus bias. It is more complicated than that.


Steve

[fwcetus]

Yes, as long as the lens properly supports the "data" contact on the mount to provide a lens id.

OK, then my question(s) maybe should be "Do third-party lenses generally do so, or is it age-of-the-lens dependent, or...?".

Since the K-3 "recognizes" the lens, in that it remembers the setting I'd put in place, does that mean that the "data" contact should be working on the lens? But, if it is, then why has the setting no effect at all on focus (even when I change the setting to +10 or to -10)?

Be aware that fine focus adjust is not the same as adjusting focus bias. It is more complicated than that.

Understood. I was (mistakenly) using a generic "focus bias" terminology, without even realizing that there is a specific meaning usually intended by it. (A little knowledge is a something-or-other thing, or however that cliche goes...)

[stevebrot]

OK, then my question(s) maybe should be "Do third-party lenses generally do so, or is it age-of-the-lens dependent, or...?".

Since the K-3 "recognizes" the lens, in that it remembers the setting I'd put in place, does that mean that the "data" contact should be working on the lens? But, if it is, then why has the setting no effect at all on focus (even when I change the setting to +10 or to -10)?

Third-party AF lenses usually provide an id. Whether that id is valid, equivalent, and unequivocal is another matter. Your lens identifies as a Pentax-F 100-300. It is hard to say what happens if the run-time focal length status passed by the lens does not match the look-up table for that lens when attempting to apply the AF fine adjustment. If I were writing the software, I would have it fail-over to the global AF setting in that case.


Steve

[fwcetus]

Your lens identifies as a Pentax-F 100-300.

Huh? Why a "Pentax-F 100-300"?

It is hard to say what happens if the run-time focal length status passed by the lens does not match the look-up table for that lens when attempting to apply the AF fine adjustment. If I were writing the software, I would have it fail-over to the global AF setting in that case.

Well, "[having] it fail-over to the global AF setting in that case" [i.e., in the case that the K-3 doesn't have the correct needed info] is maybe what's happening (?) -- the K-3 seems to be treating the Tokina as if it's just "any old lens" (with no custom setting), since it is not changing its focus at all (note - I have no global AF adjustment change in effect).

I am hoping that some users of this or other 3rd-party lenses that they have applied AF adjustments to will chime in with their own experiences... [Hint, hint...]

[stevebrot]

Huh? Why a "Pentax-F 100-300"?

Ask the good folk at Tokina! The author of the exiftool utility has compiled a list of values for the LensType tag. That is where I got the information for your lens. Where more than one lens uses the same code, they add a "dot #" to the end of the code, though that construct is not what is passed to the camera.

Pentax Tags: LensType

I am not saying that is the definitive answer to your situation, but is a likely place to look.


Steve

[fwcetus]

Ask the good folk at Tokina! The author of the exiftool utility has compiled a list of values for the LensType tag. That is where I got the information for your lens. Where more than one lens uses the same code, they add a "dot #" to the end of the code, though that construct is not what is passed to the camera.

Pentax Tags: LensType

I am not saying that is the definitive answer to your situation, but is a likely place to look.Steve

Well, that's really an interesting list -- thanks, Steve, for that.

I would seem that many 3rd-party lenses (especially Sigma lenses, then some Tokina lenses, and then a few Tamron lenses, etc.) suffer from "tag collisions". Perhaps that's why my Tokina's AF adjustment setting is "remembered" by the K-3 but is then also "ignored" by it. (?)

[It does seem as if the K-3 "recognizes" the Tokina as being different from the Pentax, though.]

Thanks for all your insights, Steve.

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Last edited by fwcetus; 08-17-2015 at 12:58 PM.

[fwcetus]

Just an additional thought: The lack of ability (at least sometimes) to compensate for front- or back-focusing with at least some of the third-party lenses would tend to discourage investing in them...

Of course, Pentax is under no requirement to provide for such, nor (at least in a nearsighted business view) might it consider desiring to do so...

[aleonx3]

Just an additional thought: The lack of ability (at least sometimes) to compensate for front- or back-focusing with at least some of the third-party lenses would tend to discourage investing in them...

Of course, Pentax is under no requirement to provide for such, nor (at least in a nearsighted business view) might it consider desiring to do so...

That is exactly what I am thinking.... I would stay with Pentax lenses unless there is a cheaper/better option to go with off-brand lenses. Front or back focus issues can be problematic sometimes unless you have a Pentax lens. I once took all my Pentax lenses and camera to the Pentax repair center and they calibrate all my lenses to the spec with the camera (k-5).

OTOH, there is still one control on the camera that allow AF fine adjustment for "all" lenses (seems to work on manual focus lens). The "apply all" adjustment parameter appears to work quite well for all my K/M and m42 lenses.

[stevebrot]

Just an additional thought: The lack of ability (at least sometimes) to compensate for front- or back-focusing with at least some of the third-party lenses would tend to discourage investing in them...

Remembering, of course, that your lens is claiming to be a Pentax product. Any blame for the ruse failing should be taking up with Tokina.

Steve

[CJC]

My practical experience with this issue is that there are certain lenses that I could never get acceptable sharpness with when testing at maximum aperture e.g. I had to send back 2 Sigma 18-35 Art series lenses until I received one that is sharp at all focal lengths. It seems that as the cameras (K3) have gotten more sophisticated the more demanding they are of lenses thus requiring higher quality and more expensive lenses. N.B. I am a photographer not a technician. I learn these technical details and take the steps I must to achieve the results I must get in situations that cannot be redone (e.g. weddings, corporate events, etc.). Some such as a Tamron 28-75 2.8 have been spot on requiring zero adjustment in K5's and K3; that may not be true for all 28-75's or for all K5's or K3's. The world did not seem quite so complex in the days of film - perhaps someone more technical could opine on such a topic.

[fwcetus]

My practical experience with this issue is that there are certain lenses that I could never get acceptable sharpness with when testing at maximum aperture e.g. I had to send back 2 Sigma 18-35 Art series lenses until I received one that is sharp at all focal lengths. It seems that as the cameras (K3) have gotten more sophisticated the more demanding they are of lenses thus requiring higher quality and more expensive lenses. N.B. I am a photographer not a technician. I learn these technical details and take the steps I must to achieve the results I must get in situations that cannot be redone (e.g. weddings, corporate events, etc.). Some such as a Tamron 28-75 2.8 have been spot on requiring zero adjustment in K5's and K3; that may not be true for all 28-75's or for all K5's or K3's. The world did not seem quite so complex in the days of film - perhaps someone more technical could opine on such a topic.

Well, first, I should point out that this reply is not likely coming from someone "more technical" than you.

I would just add two points:

1. I eventually sold the lens that I started this thread about, due to the fact that my K-3 could not easily remember (or could too easily forget) the AF adjustment setting for it. Too bad...

2. It certainly does seem more complex nowadays -- "Back in Ye Olde Film Days of Yore" such problems were less common or at least less obvious.

Finally, I do see your point about "situations that cannot be redone" -- fortunately for me I no longer have many of those situations to fret over anymore, and, if I do happen to trash a good photo op, it's usually a "cockpit error" that is to be blamed. Oh well...

[CJC]

To prevent having to redo the tedious task of re-calibrating lenses, I made a spreadsheet with the settings for every lens and body combination that I own. I store a copy in every camera bag I own.

[fwcetus]

To prevent having to redo the tedious task of re-calibrating lenses, I made a spreadsheet with the settings for every lens and body combination that I own. I store a copy in every camera bag I own.

Good idea.

I have done about half of that -- I have a small text file with my less-than-handful of settings on it on my laptop and desktop. But, I think I should do the "other half" -- I should have a copy of it in each camera bag (and at other strategic places, too), just so that, in the field, I could quickly reset a lens-body combo, without having to realize that my list happens to be miles away...

Thanks for the tip.

[nomadkng]

Well, first, I should point out that this reply is not likely coming from someone "more technical" than you.

I would just add two points:

1. I eventually sold the lens that I started this thread about, due to the fact that my K-3 could not easily remember (or could too easily forget) the AF adjustment setting for it. Too bad...

2. It certainly does seem more complex nowadays -- "Back in Ye Olde Film Days of Yore" such problems were less common or at least less obvious.

Finally, I do see your point about "situations that cannot be redone" -- fortunately for me I no longer have many of those situations to fret over anymore, and, if I do happen to trash a good photo op, it's usually a "cockpit error" that is to be blamed. Oh well...

I'll chime in here with my personal experiences. Your K-3 IS remembering the lens, the problem most likely is that the lens combined with your K3 just did not play well together. I had an FA50 1.7 and FA28 that I could not calibrate with MY K3. The FA50 was off so badly I never did figure out if it was front or back focus. My FA28 was back focused, but I could not use the GLOBAL adjustment for help because I have a couple lenses that are close to front focus correction max.

The AF adjustments "stack", so if you are lucky to get all back focused lenses, you essentially have 20 levels of correction. However a global adjust of +10 (for back focus)would eliminate any ability to correct for front focus.

I have a bag full of Sigma lenses, plus a couple Pentax lenses and my camera remembers them all. Lens ID in EXIF is influenced, if not wholly determined, by the post processing software, so it may be Photoshop/Lightroom etc "mis-identifying" the lens. Photoshop 5.5 thinks my Sigma 50-150 is a Sigma 70-200 f2.8 and my Sigma 10-20 is a Sigma 12-24.

From a camera perspective, my K-3 can actually tell the difference between my (2) Sigma 100-300 f4 lenses, maintaining the micro AF adjustments for each, so there's obviously a lot more information being communicated than just a generic lens type.