AF not reliable with wide angle lenses

Paulo · 12-28-2020, 04:36 PM

Hi All,

currently I'm an owner of KP dslr. Since the beginning I've been struggling with not reliable AF (via viewfider) with WA lens. More WA the lens is more problems I have. E.g. da*11-18 set to 18mm is quite OK whereas set to 11mm starts producing ~30-40% of totally missed shots (bigger or lesser front focus). Similar situation happens with DA15 and short end of da20-40. I found that most of missed shots are made when I pointed the camera to the high contrast scenes - tree branches or street lamps with bright sky in background. Tried to mitigate the issue and calibrate BF/AF but unfortunately without bigger success. Focal lengths equal to or higher than 35mm work almost perfect. I had the same problems with my previous camera - K-3II. I use spot AF.S only.

Have you ever faced similar problems with your cameras? If so, how have you dealt with that? For me it is really frustrating, I even think of resigning from Pentax and finding system with properly working AF.

Regards,
Paulo

**robgski** · 12-28-2020, 05:02 PM

You are using a wide angle lens, what would you like it to focus on? Select the right type of AF setting.
How much of the scene do you want in focus, make sure you have the right Aperture to ensure adequate depth of field.

Paulo · 12-28-2020, 05:16 PM

I would like the camera to focus e.g. on the tree in the middle on the frame. My expectation is that in normal condition this camera will do it. More clearly - having the subject 40m away from me I want the AF to set the lens properly i.e. on ~40m distance (actually it would be almost infinity on WA lens) but the camera sets the distance, let say, on 5 meters. Right aperture has nothing to do in this case.

> Select the right type of AF setting
could you please provide more details? What AF settings do you mean?

Regards,
Paulo

MikeMcE · 12-28-2020, 05:22 PM

Is your focus area the whole screen or have you adjusted it to the center 9 squares? I set mine for the center for my wants, so I can focus on a bird not the background. A ultra wide (11mm) is seeing an awful lot .

Hang up and DRIVE!

Paulo · 12-28-2020, 05:32 PM

As mentioned in my the 1st post I use spot AF.S only. It works perfectly with da*300 for nature even with TC 1.4x. The only problem I have relates to WA lenses.

**UncleVanya** · 12-28-2020, 05:57 PM

Originally posted by Paulo

As mentioned in my the 1st post I use spot AF.S only. It works perfectly with da*300 for nature even with TC 1.4x. The only problem I have relates to WA lenses.

You mentioned centered subjects, I otherwise I might have suggested field curvature.

What happens if you try live view does the focus work more accurately?

Paulo · 12-28-2020, 06:17 PM

Apologize for confusing you!

Life view also works perfectly. Pictures are pin sharp regardless which lens is attached to the body.

**UncleVanya** · 12-28-2020, 06:20 PM

Originally posted by Paulo

Apologize for confusing you!

Life view also works perfectly. Pictures are pin sharp regardless which lens is attached to the body.

Ok. That narrows it down. I’d upload some to Flickr or another sharing site with full Exif. Both those that failed and those that worked. Maybe - not promising anything - maybe an answer can come out of this. I personally haven’t seen this in my DA 12-24 or DA 14 or DA 15 on my K-3. It’s also possible I am not as critical and may be missing something.

Paulo · 12-28-2020, 06:32 PM

Understood. I'll make some tests during incoming days (if weather allows me) and post here link to results.

BTW you would be critical if you found your pics totally soft...

Regards,
Paulo

stevebrot · 12-28-2020, 06:36 PM

Originally posted by Paulo

Have you ever faced similar problems with your cameras?

A good rule of thumb is to expect similar performance from your camera's AF as you might from manual focus.* Strangely enough, as the object field widens, the ability of the PDAF system to detect out of focus within that field decreases with resulting decrease in precision (ability to assign the same plane of focus on multiple attempts). Of course, the same is true for manual focus, even with viewfinders having a focus aid (e.g. split image). It is that last that provides a clear reason in that the PDAF sensor sites work on the same principle as the split-image.

In more simple terms, the behavior is expected. Something similar happens when attempting PDAF or manual focus on relatively distant objects with longer focal lengths (say a fence post at 200 meters with 35mm focal length using your KP).

Steve

* Most people have some degree of difficulty focusing a 20mm and shorter focal length to a 24x36mm FF frame without magnification. I have a manual focus 14mm and it is a beast to do fine focus with even with magnified live view on my K-3.

**blues_hawk** · 12-28-2020, 06:38 PM

Originally posted by Paulo

I had the same problems with my previous camera - K-3II.

So it's not af settings, and not the frame. Do you have it set to force shutter by any chance?
I've had to learn to half shutter and verify focus before firing on my K-50 or use the verify focus setting that keeps it from firing oof, which I don't use due to the risk of missing something important. The setting is in the extra menu's on my cameras but I'm not sure about the new ones.

stevebrot · 12-28-2020, 06:51 PM

Originally posted by Paulo

BTW you would be critical if you found your pics totally soft...

This is starting to sound less like a beginner help request and more like a challenge. Could you share some examples to an outside download site, RAW or full size JPEG with EXIF intact? Choose a subject at center at about 2 meters distance shooting at 11mm focal length.

Steve

tibbitts · 12-28-2020, 06:55 PM

I think this is a universal problem with wide angle lenses, at least on the Pentax bodies I have. But I only have a limited number of wide angle lenses to test with, obviously.

Question: are you saying that live view is accurate? That's been my experience - except for a few difficult cases. The worst for me has been lumber - even knots in lumber, which makes no sense.

---------- Post added 12-28-2020 at 08:05 PM ----------

Originally posted by Paulo

Apologize for confusing you!

Life view also works perfectly. Pictures are pin sharp regardless which lens is attached to the body.

Live view AF or MF?

I have about 98% success with live view AF, and very limited success (50%?) with viewfinder AF. But that's only where some accuracy is required, so at f16 viewfinder AF starts looking okay. Viewfinder AF does usually get somewhere in the ballpark. So whenever I have time I use MF or live view AF. I do have one situation where I have easily reproducible live view AF failure, though, but only with one lens. In that same situation, viewfinder AF is useless with any lens I've tried.

**TwoUptons** · 12-29-2020, 08:10 AM

Did you calibrate your camera af to the lens?
My 16-50 was terrible when I first got it. Fantastic once I adjusted the af...

Weirdly, my 18-55 never had an issue... maybe it was the smaller aperture, maybe it was just in better agreement with the camera to begin with.

-Eric

house · 12-29-2020, 08:43 AM

Originally posted by Paulo

Hi All,

currently I'm an owner of KP dslr. Since the beginning I've been struggling with not reliable AF (via viewfider) with WA lens. More WA the lens is more problems I have. E.g. da*11-18 set to 18mm is quite OK whereas set to 11mm starts producing ~30-40% of totally missed shots (bigger or lesser front focus). Similar situation happens with DA15 and short end of da20-40. I found that most of missed shots are made when I pointed the camera to the high contrast scenes - tree branches or street lamps with bright sky in background. Tried to mitigate the issue and calibrate BF/AF but unfortunately without bigger success. Focal lengths equal to or higher than 35mm work almost perfect. I had the same problems with my previous camera - K-3II. I use spot AF.S only.

Have you ever faced similar problems with your cameras? If so, how have you dealt with that? For me it is really frustrating, I even think of resigning from Pentax and finding system with properly working AF.

Regards,
Paulo

I shot mainly 15-50mm (primes) on apsc and can't say i had af issues. Probably 100k images.
How do you know it's a AF issue rather than soft lenses? 40m with a UWA lens it's pretty hard to tell where focus is. Can you find in focus areas in the affected shots?

I have a hunch ibis can fail with uwa's but never got conclusive proof.

12-28-2020, 04:36 PM	#1
Paulo Forum Member Join Date: Jan 2012 Posts: 74	AF not reliable with wide angle lenses Hi All, currently I'm an owner of KP dslr. Since the beginning I've been struggling with not reliable AF (via viewfider) with WA lens. More WA the lens is more problems I have. E.g. da*11-18 set to 18mm is quite OK whereas set to 11mm starts producing ~30-40% of totally missed shots (bigger or lesser front focus). Similar situation happens with DA15 and short end of da20-40. I found that most of missed shots are made when I pointed the camera to the high contrast scenes - tree branches or street lamps with bright sky in background. Tried to mitigate the issue and calibrate BF/AF but unfortunately without bigger success. Focal lengths equal to or higher than 35mm work almost perfect. I had the same problems with my previous camera - K-3II. I use spot AF.S only. Have you ever faced similar problems with your cameras? If so, how have you dealt with that? For me it is really frustrating, I even think of resigning from Pentax and finding system with properly working AF. Regards, Paulo

12-28-2020, 06:36 PM	#10
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Paulo Have you ever faced similar problems with your cameras? A good rule of thumb is to expect similar performance from your camera's AF as you might from manual focus.* Strangely enough, as the object field widens, the ability of the PDAF system to detect out of focus within that field decreases with resulting decrease in precision (ability to assign the same plane of focus on multiple attempts). Of course, the same is true for manual focus, even with viewfinders having a focus aid (e.g. split image). It is that last that provides a clear reason in that the PDAF sensor sites work on the same principle as the split-image. In more simple terms, the behavior is expected. Something similar happens when attempting PDAF or manual focus on relatively distant objects with longer focal lengths (say a fence post at 200 meters with 35mm focal length using your KP). Steve * Most people have some degree of difficulty focusing a 20mm and shorter focal length to a 24x36mm FF frame without magnification. I have a manual focus 14mm and it is a beast to do fine focus with even with magnified live view on my K-3. Last edited by stevebrot; 12-28-2020 at 06:42 PM.

12-28-2020, 06:51 PM	#12
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Paulo BTW you would be critical if you found your pics totally soft... This is starting to sound less like a beginner help request and more like a challenge. Could you share some examples to an outside download site, RAW or full size JPEG with EXIF intact? Choose a subject at center at about 2 meters distance shooting at 11mm focal length. Steve Last edited by stevebrot; 12-28-2020 at 07:04 PM.

12-28-2020, 06:55 PM	#13
tibbitts Pentaxian Join Date: Apr 2007 Location: Oklahoma USA Posts: 2,193	I think this is a universal problem with wide angle lenses, at least on the Pentax bodies I have. But I only have a limited number of wide angle lenses to test with, obviously. Question: are you saying that live view is accurate? That's been my experience - except for a few difficult cases. The worst for me has been lumber - even knots in lumber, which makes no sense. ---------- Post added 12-28-2020 at 08:05 PM ---------- Originally posted by Paulo Apologize for confusing you! Life view also works perfectly. Pictures are pin sharp regardless which lens is attached to the body. Live view AF or MF? I have about 98% success with live view AF, and very limited success (50%?) with viewfinder AF. But that's only where some accuracy is required, so at f16 viewfinder AF starts looking okay. Viewfinder AF does usually get somewhere in the ballpark. So whenever I have time I use MF or live view AF. I do have one situation where I have easily reproducible live view AF failure, though, but only with one lens. In that same situation, viewfinder AF is useless with any lens I've tried. Last edited by tibbitts; 12-28-2020 at 07:06 PM.

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12-28-2020, 05:02 PM	#2
robgski Loyal Site Supporter Join Date: Nov 2012 Location: Shenandoah Valley, Virginia Photos: Gallery \| Albums Posts: 8,796	You are using a wide angle lens, what would you like it to focus on? Select the right type of AF setting. How much of the scene do you want in focus, make sure you have the right Aperture to ensure adequate depth of field.

12-28-2020, 05:16 PM	#3
Paulo Forum Member Join Date: Jan 2012 Posts: 74 Original Poster	I would like the camera to focus e.g. on the tree in the middle on the frame. My expectation is that in normal condition this camera will do it. More clearly - having the subject 40m away from me I want the AF to set the lens properly i.e. on ~40m distance (actually it would be almost infinity on WA lens) but the camera sets the distance, let say, on 5 meters. Right aperture has nothing to do in this case. > Select the right type of AF setting could you please provide more details? What AF settings do you mean? Regards, Paulo

12-28-2020, 05:22 PM	#4
MikeMcE Pentaxian Join Date: Jun 2020 Photos: Albums Posts: 1,093	Is your focus area the whole screen or have you adjusted it to the center 9 squares? I set mine for the center for my wants, so I can focus on a bird not the background. A ultra wide (11mm) is seeing an awful lot . Hang up and DRIVE!

12-28-2020, 05:32 PM	#5
Paulo Forum Member Join Date: Jan 2012 Posts: 74 Original Poster	As mentioned in my the 1st post I use spot AF.S only. It works perfectly with da*300 for nature even with TC 1.4x. The only problem I have relates to WA lenses.

12-28-2020, 05:57 PM	#6
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,401	Originally posted by Paulo As mentioned in my the 1st post I use spot AF.S only. It works perfectly with da*300 for nature even with TC 1.4x. The only problem I have relates to WA lenses. You mentioned centered subjects, I otherwise I might have suggested field curvature. What happens if you try live view does the focus work more accurately?

12-28-2020, 06:17 PM	#7
Paulo Forum Member Join Date: Jan 2012 Posts: 74 Original Poster	Apologize for confusing you! Life view also works perfectly. Pictures are pin sharp regardless which lens is attached to the body.

12-28-2020, 06:20 PM	#8
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,401	Originally posted by Paulo Apologize for confusing you! Life view also works perfectly. Pictures are pin sharp regardless which lens is attached to the body. Ok. That narrows it down. I’d upload some to Flickr or another sharing site with full Exif. Both those that failed and those that worked. Maybe - not promising anything - maybe an answer can come out of this. I personally haven’t seen this in my DA 12-24 or DA 14 or DA 15 on my K-3. It’s also possible I am not as critical and may be missing something.

12-28-2020, 06:32 PM	#9
Paulo Forum Member Join Date: Jan 2012 Posts: 74 Original Poster	Understood. I'll make some tests during incoming days (if weather allows me) and post here link to results. BTW you would be critical if you found your pics totally soft... Regards, Paulo

12-28-2020, 06:38 PM	#11
blues_hawk Site Supporter Join Date: Jul 2016 Location: Patrick Co. Virginia Photos: Gallery \| Albums Posts: 1,534	Originally posted by Paulo I had the same problems with my previous camera - K-3II. So it's not af settings, and not the frame. Do you have it set to force shutter by any chance? I've had to learn to half shutter and verify focus before firing on my K-50 or use the verify focus setting that keeps it from firing oof, which I don't use due to the risk of missing something important. The setting is in the extra menu's on my cameras but I'm not sure about the new ones.

12-29-2020, 08:10 AM	#14
TwoUptons Loyal Site Supporter Join Date: Nov 2015 Photos: Albums Posts: 4,213	Did you calibrate your camera af to the lens? My 16-50 was terrible when I first got it. Fantastic once I adjusted the af... Weirdly, my 18-55 never had an issue... maybe it was the smaller aperture, maybe it was just in better agreement with the camera to begin with. -Eric

12-29-2020, 08:43 AM	#15
house Pentaxian Join Date: May 2015 Photos: Albums Posts: 3,306	Originally posted by Paulo Hi All, currently I'm an owner of KP dslr. Since the beginning I've been struggling with not reliable AF (via viewfider) with WA lens. More WA the lens is more problems I have. E.g. da*11-18 set to 18mm is quite OK whereas set to 11mm starts producing ~30-40% of totally missed shots (bigger or lesser front focus). Similar situation happens with DA15 and short end of da20-40. I found that most of missed shots are made when I pointed the camera to the high contrast scenes - tree branches or street lamps with bright sky in background. Tried to mitigate the issue and calibrate BF/AF but unfortunately without bigger success. Focal lengths equal to or higher than 35mm work almost perfect. I had the same problems with my previous camera - K-3II. I use spot AF.S only. Have you ever faced similar problems with your cameras? If so, how have you dealt with that? For me it is really frustrating, I even think of resigning from Pentax and finding system with properly working AF. Regards, Paulo I shot mainly 15-50mm (primes) on apsc and can't say i had af issues. Probably 100k images. How do you know it's a AF issue rather than soft lenses? 40m with a UWA lens it's pretty hard to tell where focus is. Can you find in focus areas in the affected shots? I have a hunch ibis can fail with uwa's but never got conclusive proof.