K-x front-focus with DA 35mm F2.4 AL and other manual lenses

**7samurai** · 03-17-2012, 05:34 PM

I think I got a bad copy of the 35mm f/2.4 so I'm exchanging it. It front-focus all the time at all apetures.

Which got me thinking, when I shoot manual lenses at any apeture below f/2.2, I can't rely on the focus indicator because it's always front-focus.
Is this the limitation of the K-x focus indicator? I have the same issue with both my M 50mm f/1.4 and A 50mm f/1.7.

Thanks in advance for any comments

JinDesu · 03-17-2012, 05:37 PM

If all your lenses are front focusing, you can adjust them.

RiceHigh's Pentax Blog: K-x Debug Mode Tutorial - AF Adjustment

Try doing the AF adjust and see what result you get. A bit of a tip: When doing AF adjust and changing the value, you have to hit the select button afterwards to apply it. Hitting Menu will exit without saving. And subsequent changes will be additive - if you do +10um, then +10um again, it'll be a total of 20um.

Adam · 03-17-2012, 05:41 PM

FF/BF is really only applicable to AF lenses, as the confirmation feature gives you a lot of slack.

Learn more here: Fixing Front and Back Focus - Introduction - PentaxForums.com

Are you getting the same results in live view?

**7samurai** · 03-17-2012, 06:08 PM

Originally posted by Adam

Are you getting the same results in live view?

The DA 35mm f/2.4 was FF across the board. I'll need to test the focusing using live view.
All my other auto focus lenses are fine.

Last edited by 7samurai; 03-17-2012 at 06:14 PM. Reason: misunderstanding in my reply

**7samurai** · 03-17-2012, 06:11 PM

Originally posted by JinDesu

If all your lenses are front focusing, you can adjust them.

RiceHigh's Pentax Blog: K-x Debug Mode Tutorial - AF Adjustment

Try doing the AF adjust and see what result you get. A bit of a tip: When doing AF adjust and changing the value, you have to hit the select button afterwards to apply it. Hitting Menu will exit without saving. And subsequent changes will be additive - if you do +10um, then +10um again, it'll be a total of 20um.

I'll give this a try. It seem to be out of focus by a fairly large margin to my eyes.

**7samurai** · 03-17-2012, 06:39 PM

Is the k-x debug focus correction per lens or does it affect all the lenses?

JinDesu · 03-17-2012, 06:39 PM

Affects all lenses on the k-x.

**7samurai** · 03-17-2012, 06:44 PM

Originally posted by JinDesu

Affects all lenses on the k-x.

thanks for the quick reply. I'll probably not change the focus correction since it would affect all my other lenses.

**7samurai** · 03-17-2012, 10:04 PM

Originally posted by Adam

Are you getting the same results in live view?

Adam,

Live view works fine. Sharp images. Only the autofocus seems to be fuzzy.

rawr · 03-18-2012, 02:12 AM

BF/FF is of course an issue to deal with.
But are you the original owner of the camera?

If you are not the original owner, another possibility may be that a previous owner made adjustments to the AF via the debug menu, and those adjustments are still in effect.

If you are the original owner, don't worry about what I said above

My other suggestion relates to my old bugbear - use of UV or protection filters on lenses. Poor quality filters can reduce the amount of light entering the lens, interfere with the visible and IR spectrum, add extra flare and ghosting to the image, as well as simply reduce the contrast of the scene. All of which can interfere with the efficiency of the AF sensor. If you are using UV filters on your lenses that are having AF problems, remove the filters, use a hood, and see if the problem recurs.

**7samurai** · 03-18-2012, 09:13 AM

Originally posted by rawr

BF/FF is of course an issue to deal with.
But are you the original owner of the camera?

If you are not the original owner, another possibility may be that a previous owner made adjustments to the AF via the debug menu, and those adjustments are still in effect.

If you are the original owner, don't worry about what I said above

My other suggestion relates to my old bugbear - use of UV or protection filters on lenses. Poor quality filters can reduce the amount of light entering the lens, interfere with the visible and IR spectrum, add extra flare and ghosting to the image, as well as simply reduce the contrast of the scene. All of which can interfere with the efficiency of the AF sensor. If you are using UV filters on your lenses that are having AF problems, remove the filters, use a hood, and see if the problem recurs.

I'm the original owner and I checked the setting and it was 0.
All the testing I did was without filters.

I played around with my debug and the camera seems to like +60 with the kit lenses. That setting also seems to work better with my M 50mm f/1.4 at f/1.4. The focus confirmation beep seems to be more accurate.
I think the 35mm f/2.4 likes +90 or +100. That's not good....=(

Laurentiu Cristofor · 03-18-2012, 01:51 PM

Originally posted by Adam

FF/BF is really only applicable to AF lenses, as the confirmation feature gives you a lot of slack.

I thought so too, but it's a bit more complex. If you use the AF confirmation, you are really depending on the AF system (that slack is probably affecting AF too). But furthermore, if the mirror is not properly calibrated, you can run into issues even if you ignore AF confirmation - you can focus the scene in the viewfinder, but it won't be in focus on the sensor, because of the different optical paths. And with optical confirmation, the diopter adjustment can also play a role - you can knock it out a bit and then you'll focus all wrong.

Focusing in LiveView will work better, because the optical path used for focusing is the same path used for recording. But in a DSLR, they are different, so issues can arise from that. This why I keep saying that once users move to using mirrorless cameras instead of DSLRs, we will have much fewer threads like these.

sterretje · 03-19-2012, 07:19 AM

Originally posted by 7samurai

Which got me thinking, when I shoot manual lenses at any apeture below f/2.2, I can't rely on the focus indicator because it's always front-focus.
Is this the limitation of the K-x focus indicator? I have the same issue with both my M 50mm f/1.4 and A 50mm f/1.7.

You will find that once you have 'locked' focus with those fast manual lenses, you can still turn the focus ring a little and not loose focus 'lock'. So there is a range; similar, you will find a small difference coming from infinity or from nearby. The perfect focus might be somewhere in between.

One solution is to get a split prism screen and rely on that.

Marc Sabatella · 03-19-2012, 02:30 PM

Unless you have other AF lenses that are as fast as f/2.4, then you really don't know they wouldn't exhibit FF if they were capable of f/2.4. FF errors are only visible at large enou apertures to show them.

But I've said this before, and i!ll say it again. There is absolutely nothing that could possibly be physically wrong with a lens to cause it to front focus. The camera does the focusing and the checking to see if the result is actually in focus. Nothing you could possibly do to a lens will cause it to FF. Same with BF.

That means that all FF and BF problems ever reported are either the *camera* being misadjusted, or testing error. There is no other possible explanation.

Yes, I know, this is an extrmely unpopular minority opinipn. But until someone shows me how it physiclly possible for a lens to consistently FF or BF, I maintain that it cannot.

Laurentiu Cristofor · 03-19-2012, 11:07 PM

Originally posted by Marc Sabatella

There is absolutely nothing that could possibly be physically wrong with a lens to cause it to front focus.

Focus shift is one design issue that is lens specific and can cause misfocus. Cameras focus wide open, then stop down to take a shot. A lens with focus shift would focus in the wrong place once it's stopped down, even if the camera correctly focused it wide open.

There could also be other aspects related to the AF implementation, where the camera tells the lens to focus a certain amount, but the lens changes focus more or less than it was asked to do it - if the camera doesn't double check (I know Pentax AF is supposed to, but maybe it avoids that in certain situations), then it will misfocus.

03-17-2012, 05:34 PM	#1
7samurai Site Supporter Join Date: Apr 2010 Location: Rancho Cucamonga, CA Photos: Albums Posts: 474	K-x front-focus with DA 35mm F2.4 AL and other manual lenses I think I got a bad copy of the 35mm f/2.4 so I'm exchanging it. It front-focus all the time at all apetures. Which got me thinking, when I shoot manual lenses at any apeture below f/2.2, I can't rely on the focus indicator because it's always front-focus. Is this the limitation of the K-x focus indicator? I have the same issue with both my M 50mm f/1.4 and A 50mm f/1.7. Thanks in advance for any comments

03-17-2012, 05:41 PM	#3
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,594	FF/BF is really only applicable to AF lenses, as the confirmation feature gives you a lot of slack. Learn more here: Fixing Front and Back Focus - Introduction - PentaxForums.com Are you getting the same results in live view? Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

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03-17-2012, 05:37 PM	#2
JinDesu Veteran Member Join Date: Jun 2011 Location: New York City Photos: Gallery Posts: 5,638	If all your lenses are front focusing, you can adjust them. RiceHigh's Pentax Blog: K-x Debug Mode Tutorial - AF Adjustment Try doing the AF adjust and see what result you get. A bit of a tip: When doing AF adjust and changing the value, you have to hit the select button afterwards to apply it. Hitting Menu will exit without saving. And subsequent changes will be additive - if you do +10um, then +10um again, it'll be a total of 20um.

03-17-2012, 06:08 PM	#4
7samurai Site Supporter Join Date: Apr 2010 Location: Rancho Cucamonga, CA Photos: Albums Posts: 474 Original Poster	Originally posted by Adam Are you getting the same results in live view? The DA 35mm f/2.4 was FF across the board. I'll need to test the focusing using live view. All my other auto focus lenses are fine. Last edited by 7samurai; 03-17-2012 at 06:14 PM. Reason: misunderstanding in my reply

03-17-2012, 06:11 PM	#5
7samurai Site Supporter Join Date: Apr 2010 Location: Rancho Cucamonga, CA Photos: Albums Posts: 474 Original Poster	Originally posted by JinDesu If all your lenses are front focusing, you can adjust them. RiceHigh's Pentax Blog: K-x Debug Mode Tutorial - AF Adjustment Try doing the AF adjust and see what result you get. A bit of a tip: When doing AF adjust and changing the value, you have to hit the select button afterwards to apply it. Hitting Menu will exit without saving. And subsequent changes will be additive - if you do +10um, then +10um again, it'll be a total of 20um. I'll give this a try. It seem to be out of focus by a fairly large margin to my eyes.

03-17-2012, 06:39 PM	#6
7samurai Site Supporter Join Date: Apr 2010 Location: Rancho Cucamonga, CA Photos: Albums Posts: 474 Original Poster	Is the k-x debug focus correction per lens or does it affect all the lenses?

03-17-2012, 06:44 PM	#8
7samurai Site Supporter Join Date: Apr 2010 Location: Rancho Cucamonga, CA Photos: Albums Posts: 474 Original Poster	Originally posted by JinDesu Affects all lenses on the k-x. thanks for the quick reply. I'll probably not change the focus correction since it would affect all my other lenses.

03-17-2012, 10:04 PM	#9
7samurai Site Supporter Join Date: Apr 2010 Location: Rancho Cucamonga, CA Photos: Albums Posts: 474 Original Poster	Originally posted by Adam Are you getting the same results in live view? Adam, Live view works fine. Sharp images. Only the autofocus seems to be fuzzy.

03-18-2012, 02:12 AM	#10
rawr Veteran Member Join Date: Jun 2009 Posts: 11,913	BF/FF is of course an issue to deal with. But are you the original owner of the camera? If you are not the original owner, another possibility may be that a previous owner made adjustments to the AF via the debug menu, and those adjustments are still in effect. If you are the original owner, don't worry about what I said above My other suggestion relates to my old bugbear - use of UV or protection filters on lenses. Poor quality filters can reduce the amount of light entering the lens, interfere with the visible and IR spectrum, add extra flare and ghosting to the image, as well as simply reduce the contrast of the scene. All of which can interfere with the efficiency of the AF sensor. If you are using UV filters on your lenses that are having AF problems, remove the filters, use a hood, and see if the problem recurs.

03-18-2012, 09:13 AM	#11
7samurai Site Supporter Join Date: Apr 2010 Location: Rancho Cucamonga, CA Photos: Albums Posts: 474 Original Poster	Originally posted by rawr BF/FF is of course an issue to deal with. But are you the original owner of the camera? If you are not the original owner, another possibility may be that a previous owner made adjustments to the AF via the debug menu, and those adjustments are still in effect. If you are the original owner, don't worry about what I said above My other suggestion relates to my old bugbear - use of UV or protection filters on lenses. Poor quality filters can reduce the amount of light entering the lens, interfere with the visible and IR spectrum, add extra flare and ghosting to the image, as well as simply reduce the contrast of the scene. All of which can interfere with the efficiency of the AF sensor. If you are using UV filters on your lenses that are having AF problems, remove the filters, use a hood, and see if the problem recurs. I'm the original owner and I checked the setting and it was 0. All the testing I did was without filters. I played around with my debug and the camera seems to like +60 with the kit lenses. That setting also seems to work better with my M 50mm f/1.4 at f/1.4. The focus confirmation beep seems to be more accurate. I think the 35mm f/2.4 likes +90 or +100. That's not good....=(

03-18-2012, 01:51 PM	#12
Laurentiu Cristofor Banned Join Date: Nov 2009 Location: WA Photos: Albums Posts: 3,055	Originally posted by Adam FF/BF is really only applicable to AF lenses, as the confirmation feature gives you a lot of slack. I thought so too, but it's a bit more complex. If you use the AF confirmation, you are really depending on the AF system (that slack is probably affecting AF too). But furthermore, if the mirror is not properly calibrated, you can run into issues even if you ignore AF confirmation - you can focus the scene in the viewfinder, but it won't be in focus on the sensor, because of the different optical paths. And with optical confirmation, the diopter adjustment can also play a role - you can knock it out a bit and then you'll focus all wrong. Focusing in LiveView will work better, because the optical path used for focusing is the same path used for recording. But in a DSLR, they are different, so issues can arise from that. This why I keep saying that once users move to using mirrorless cameras instead of DSLRs, we will have much fewer threads like these.

03-19-2012, 07:19 AM	#13
sterretje Veteran Member Join Date: Dec 2008 Location: Roodepoort, South Africa Photos: Gallery \| Albums Posts: 3,561	Originally posted by 7samurai Which got me thinking, when I shoot manual lenses at any apeture below f/2.2, I can't rely on the focus indicator because it's always front-focus. Is this the limitation of the K-x focus indicator? I have the same issue with both my M 50mm f/1.4 and A 50mm f/1.7. You will find that once you have 'locked' focus with those fast manual lenses, you can still turn the focus ring a little and not loose focus 'lock'. So there is a range; similar, you will find a small difference coming from infinity or from nearby. The perfect focus might be somewhere in between. One solution is to get a split prism screen and rely on that.

03-19-2012, 02:30 PM	#14
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,685	Unless you have other AF lenses that are as fast as f/2.4, then you really don't know they wouldn't exhibit FF if they were capable of f/2.4. FF errors are only visible at large enou apertures to show them. But I've said this before, and i!ll say it again. There is absolutely nothing that could possibly be physically wrong with a lens to cause it to front focus. The camera does the focusing and the checking to see if the result is actually in focus. Nothing you could possibly do to a lens will cause it to FF. Same with BF. That means that all FF and BF problems ever reported are either the camera being misadjusted, or testing error. There is no other possible explanation. Yes, I know, this is an extrmely unpopular minority opinipn. But until someone shows me how it physiclly possible for a lens to consistently FF or BF, I maintain that it cannot.

03-19-2012, 11:07 PM	#15
Laurentiu Cristofor Banned Join Date: Nov 2009 Location: WA Photos: Albums Posts: 3,055	Originally posted by Marc Sabatella There is absolutely nothing that could possibly be physically wrong with a lens to cause it to front focus. Focus shift is one design issue that is lens specific and can cause misfocus. Cameras focus wide open, then stop down to take a shot. A lens with focus shift would focus in the wrong place once it's stopped down, even if the camera correctly focused it wide open. There could also be other aspects related to the AF implementation, where the camera tells the lens to focus a certain amount, but the lens changes focus more or less than it was asked to do it - if the camera doesn't double check (I know Pentax AF is supposed to, but maybe it avoids that in certain situations), then it will misfocus.