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07-12-2008, 10:41 PM   #1
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Does K20D's AF adjustment get applied to MF lenses?

Does the "Apply All" get applied to MF lenses?
I finally broke down and printed a focus test chart, mostly being curious how the adjustment works, at +-0 and -5, i seem to get the same exact amount of front focus on that chart.
Even if "Apply One" is not available for this KA mount lens, i was hoping the "Apply All" would apply, then after that is tweaked i would have gone tweak the AF lens' "Apply One" to allow all lenses to be happy.

Should it work with MF lenses, since they use the AF system's sensors for focus confirmation?
Yes, i am on a tripod, i am not using MLU, considering i take 3 shots per adjustment, they shouldn't all look the same between 0 and -5, no?

07-12-2008, 11:28 PM   #2
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Interestingly where i stopped with "Apply All" (-5) just about any focal length of the 50-135 is perfect, (i noticed some front focusing on my first day out with the lens) and on the 16-50 it's a mixed bag, at 31mm and 50mm, reasonably well focused, 16mm blows my mind it's so far back it's not even on the chart, but since i pick up the leather texture on the couch on which the chart was laying i know the lens isn't soft, just way way back focused.
I wonder if i should focus it like i used to focus the Sigma 10-20, set to 1m, stop down, shoot, good shot, seems like it would work here too.

For what it's worth, moving in closer at 16mm makes it hit that center line on the chart just as well.
In other words it's time to hit the photostore tomorrow, so i can have a bag where the 16-50, 50-135 and K20D fit in a way that allows me to use the 58/1.4 w/o unearthing it from way down below.
As nice as the DA* lenses are and as well as they perform, it's the Nokton i really want to take out, the other two will just see enough daylight to make sure my late night focus chart tomfoolery is not having any ill effects in real life.

To my original question, i may have approached the focus point from two different directions, once from infinity and once from MFD, which wide open seems to be able to influence the AF system enough to have made a +-0 look like a -5 when both use opposite approaches.

Last edited by morfic; 07-12-2008 at 11:41 PM. Reason: Just add a ton more w/o another post.
07-12-2008, 11:40 PM   #3
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QuoteOriginally posted by morfic Quote
Does the "Apply All" get applied to MF lenses?
I finally broke down and printed a focus test chart, mostly being curious how the adjustment works, at +-0 and -5, i seem to get the same exact amount of front focus on that chart.
Even if "Apply One" is not available for this KA mount lens, i was hoping the "Apply All" would apply, then after that is tweaked i would have gone tweak the AF lens' "Apply One" to allow all lenses to be happy.

Should it work with MF lenses, since they use the AF system's sensors for focus confirmation?
Yes, i am on a tripod, i am not using MLU, considering i take 3 shots per adjustment, they shouldn't all look the same between 0 and -5, no?
I have only K200d only. But in HK there was one case of a P-fans. He used K20d. His case was quite similar to yours. He adjusted +4 on one day but the other day it seemed to be -3 better etc.

I had front focus problem before. After adjustment by Pentax's service agent, it seemed that the focus now worked fine for the Kit Mk2 as well as a DA 35mm F2.8 Macro Limited up to his moment.
(Only thing still annoyed me now was the "hitting a hard stop at infinte" issue of my kit lens, see thread
https://www.pentaxforums.com/forums/pentax-dslr-discussion/31786-will-your-k2...have-like.html)
But I think it was just a matter of factory QC and insufficient margins of the body + the kit lens mixed together. My DA35mm F2.8 macro does not have the problem of "hitting a hard stop" when focus it to distant objects.

Therefore, If adjustment by within the +/-5 range on your K20d manual had failed, the AF sensor position should better be re-adjusted by service centre first. Therefore, it is suggested to send the stuff to the service centre to do the adjustment/finetune.

Noticed also that when you do the fine-tune, it's had better to chioce the largest Aperature. Also, it is supposed making a larger angle of shot towards the chart paper as well.

While waiting for other K20d users Feedback, hope these information help a little

Last edited by ckanthon; 07-12-2008 at 11:57 PM.
07-12-2008, 11:52 PM   #4
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QuoteOriginally posted by morfic Quote
Interestingly where i stopped with "Apply All" (-5) just about any focal length of the 50-135 is perfect, (i noticed some front focusing on my first day out with the lens) and on the 16-50 it's a mixed bag, at 31mm and 50mm, reasonably well focused, 16mm blows my mind it's so far back it's not even on the chart, but since i pick up the leather texture on the couch on which the chart was laying i know the lens isn't soft, just way way back focused.
I wonder if i should focus it like i used to focus the Sigma 10-20, set to 1m, stop down, shoot, good shot, seems like it would work here too.

For what it's worth, moving in closer at 16mm makes it hit that center line on the chart just as well.
In other words it's time to hit the photostore tomorrow, so i can have a bag where the 16-50, 50-135 and K20D fit in a way that allows me to use the 58/1.4 w/o unearthing it from way down below.
As nice as the DA* lenses are and as well as they perform, it's the Nokton i really want to take out, the other two will just see enough daylight to make sure my late night focus chart tomfoolery is not having any ill effects in real life.

To my original question, i may have approached the focus point from two different directions, once from infinity and once from MFD, which wide open seems to be able to influence the AF system enough to have made a +-0 look like a -5 when both use opposite approaches.
When you adjust the focus at 16mm and wide open Aparture (such as f2.8), you might have the problem complicated by the sensor's limited capability. As suggested by Rice, the sensor is not perfectly doing its job as a "f2.8" sensor can do. Then, your focus setting could already be adjusted OK. But the sensor simply moved away (because it behaves imperfectly when it saw a f2.8 imperfect focus)!!
Could these be one of the reason that you could focus OK at 31m, 50m while not OK at 16mm ?!?


Noticed also that in TW, one K10d user reported that the AF SDM of DA*16-50, in fact, it "overshot" a little. It did not stop as quick as it should be. Then it could also led to a back-focusing. This overshot can be verified by trying the Manual Focus.


Last edited by ckanthon; 07-13-2008 at 12:02 AM.
07-13-2008, 12:11 AM   #5
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I am reasonably happy with all tested focal lengths and their hitting the mark.
I am not sure if overshooting due to SDM is possible, doesn't Pentax kind of ritsch ratsch click around the focus point, like a rough and a fine movement. Neither SDM lens is all that quick.

I think what i saw is results of improper use, if i focus to infinity with a 16mm lens, likely i have it well stopped down, not at f/2.8 and what i saw will not show in a picture. (Plus during day light shots, where i would use it at infinity, i have better contrast due to better light.)
When i shoot something close up at 16mm then i know even at f/2.8 it really nails focus. (My guess is the better local contrast at closer range is what allowed it to hit the mark afterall indoors at this light)

And back to my manual focused lens, that one too seems to nail focus if i approach it always from the same direction, even if it is not the direction i would have expected, approaching it from MFD, i have LESS front focus, while i would have expected more (my thinking here would be that the sensor gives me a range where the hex focus indicator stays lit, approaching it from the MFD i would get the closest end of the focus range and approaching it from infinity would give me the farther end of the focus range. First time i thought i made a msitake when i got results opposite to my expectations, so i repeated it again,and again those shots taken when approaching focus point from MFD are those better focused)

The Nokton now: http://www.zerorealm.org/infocus.jpg (The alignment went south when i had to move everything to accomodate the 50-135's distant MFD :/)

I see no reason to send this camera anywhere at this point.

Not sure what the sensor is not doing as a f/2.8 sensor? Got any link what you are refering to?
07-13-2008, 12:27 AM   #6
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QuoteOriginally posted by morfic Quote
I think what i saw is results of improper use, if i focus to infinity with a 16mm lens, likely i have it well stopped down, not at f/2.8 and what i saw will not show in a picture. (Plus during day light shots, where i would use it at infinity, i have better contrast due to better light.)
When i shoot something close up at 16mm then i know even at f/2.8 it really nails focus. (My guess is the better local contrast at closer range is what allowed it to hit the mark afterall indoors at this light)

Not sure what the sensor is not doing as a f/2.8 sensor? Got any link what you are refering to?
Hi, Thanks for your suggestion in this regard. whereas when I said "hitting a hard stop when I used wide angle at f2.8 to shot distant object". What I also meant was that it already hitted the stop-end when I focused to objects 8m away. Therefore, I think using f2.8 and wide angle to shot like this is not 100% my "mis-use". Now I carefully select my F-number at wide angle shot. F8 would be fine. Anyway, it is not suppose to hit that end

I also not sure, but the AF sensor of K200d seemed reacted a little differently when it saw wide angle f3.5 focus of my kit mk2.

Last edited by ckanthon; 07-13-2008 at 01:07 AM.
07-13-2008, 12:34 AM   #7
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QuoteOriginally posted by morfic Quote
I am not sure if overshooting due to SDM is possible, doesn't Pentax kind of ritsch ratsch click around the focus point, like a rough and a fine movement. Neither SDM lens is all that quick.
It was just what a saw from a blog in tw that a guy tested DA*16-50 and DA*50-135. He said the earlier lenses with SDM seemed "run overshot a little" when he compared then with a sigma lens.
When taken shots with the same settings, the sigma lens was sharper whereas there was a little bit blurr seen on the DA*50-135. Test the DA*55-135 using MF seemed OK. He posted several pictures. I did not test these but just saw his review.

Last edited by ckanthon; 07-13-2008 at 01:14 PM.
07-13-2008, 12:37 AM   #8
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"Misuse", i was entirely refering to myself.
My 16-50 isn't hitting anything, AF lenses should find infinity focus before the hard stop, i agree there, AF lenses are allowed to go past infinity for that reason.

07-13-2008, 12:46 AM   #9
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HaHa...My misunderstand then... very kindly of you to re-assurance me...

But I am still did not get a full picture about your concerns stated...

Did you got problem(s) on MF lens Nokton 58/1.4 only (when approaching from different directions: from "inifity" side or from "MFD" side?

Or else,. What adjustment setting 0 or 5 affected your picture shot?

Just intereted to know...

Last edited by ckanthon; 07-13-2008 at 01:11 AM.
07-13-2008, 08:16 AM   #10
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While testing the MF lens, i saw no difference going from 0 to -5, since i did not notice i had changed approach direction it seems.
Approaching it from MFD i now get a well focused test chart.
Before adjusting it to -5 it was way front focused (similar to the 50-135 front focus)
Now, after approaching focus always from the same side on the MF lens, and checking the 2 AF lenses, focus seems to be always on with the -5 setting.
What's lacking is testing them in the field instead of on a test chart.
07-13-2008, 08:46 AM   #11
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Hi morfic,

Thanks for your clarification. I think it is a good reference scheme for the K20d fous fine-tune.

This also help me to understand more about the AF senoring behaviour.. Thank you.

BTW, Pentax should had better have such scheme on the manual for K20d user to refer to!!

I think "apply all" is "applied all"
07-13-2008, 09:23 AM   #12
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QuoteOriginally posted by morfic Quote

Not sure what the sensor is not doing as a f/2.8 sensor? Got any link what you are refering to?
Canon cameras use 2 different types of sensors as in this diagram for 1D, 1DS camera:


Canon EOS-1D Mark III Digital Camera Optics - Hands-On Preview - The Imaging Resource!

There are a bunch of different sensors due to lens characteristics. Some will focus w/ fast lenses better than others.
Some will focus in dimmer light than the others ect.
Canon's fast lens sensors use a different baseline for AF detect w/ fast lenses. I'll have to find you the reference for it but fast lenses need different AF point configurations.
07-13-2008, 10:55 AM   #13
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MFD to subject improves focus accuracy

QuoteOriginally posted by morfic Quote
And back to my manual focused lens, that one too seems to nail focus if i approach it always from the same direction, even if it is not the direction i would have expected, approaching it from MFD, i have LESS front focus, while i would have expected more
i've noticed this on my k10d also. when i focus on my hand (MFD) then the subject, it seems to acquire the focus i want more accurately. when i don't think about it, it seems to back-focus w/ some regularity (this refers mainly to my FA35-2, but the 55 and 135 also, i think).
07-13-2008, 11:08 AM   #14
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QuoteOriginally posted by jeffkrol Quote
Canon cameras use 2 different types of sensors as in this diagram for 1D, 1DS camera:


Canon EOS-1D Mark III Digital Camera Optics - Hands-On Preview - The Imaging Resource!

There are a bunch of different sensors due to lens characteristics. Some will focus w/ fast lenses better than others.
Some will focus in dimmer light than the others ect.
Canon's fast lens sensors use a different baseline for AF detect w/ fast lenses. I'll have to find you the reference for it but fast lenses need different AF point configurations.
I guess what i meant is, how going to a faster lens would make things less accurate, a f/2.8 sensor needs at least f/2.8 or larger.
Now if Mr RiceHigh meant to say it's more a f/2.5 or f/2.2 sensor, ok, going from a kit lens at f/3.5 to a f/2.8 lens should still make things better not worse, so i am not sure what he means, that said he was only quoted, and has not said anything to this thread at all. So my question was more regarding what it is he said, not how the max lens aperture affects sensor accuracy in general (thanks though, it was interesting the 1D3 has still "only" a f/4 center AF cross type sensor, just like the EOS3 had, i was thinking they improved on this since the EOS3)
07-13-2008, 11:09 AM   #15
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QuoteOriginally posted by architorture Quote
i've noticed this on my k10d also. when i focus on my hand (MFD) then the subject, it seems to acquire the focus i want more accurately. when i don't think about it, it seems to back-focus w/ some regularity (this refers mainly to my FA35-2, but the 55 and 135 also, i think).
Good to know i am not the only one to notice it.
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