AF issues with K20D

stianb · 12-18-2009, 03:58 PM

I feel that most of the portraits I take with my K20D is ever so slightly out of focus. I wonder if anyone else has experienced the same problem and if so, if there are any ways to be corrected. I'm using the 50-135 and a 100mm macro lense for portraits.

I'm not inclined to believe it's a problem with the photographer anymore, since I've experimented a lot.

Damn Brit · 12-18-2009, 04:01 PM

Welcome to the forum.

Examples please with exif data. We can't determine anything from a few words.

We're not inclined to believe it's not the photographer without visual evidence because any of us are fallible to missing something, a picture doesn't lie.

It is possible that you are getting front or back focus and you can make adjustments on your K20, you'll find details in the manual. If you look around on PentaxForums, you'll find plenty of discussions about the subject.

Raybo · 12-18-2009, 05:39 PM

I get quite a few OOF images with my K20 and it's mostly due to me.

Ash · 12-18-2009, 09:58 PM

Welcome to the forum.
Do post some examples and tell us if it's consistent back or front focusing happening with one, some or all your lenses.

Raybo · 12-18-2009, 10:10 PM

I just wish Pentax had a smooth diopter setting instead of the clicky style.
My diopter just happens to be on one of in between settings and it's really hard to get it just right.

jolee1990 · 12-19-2009, 08:04 AM

i did too, but i still don't know the reason so i am gonna post some pics up later

Marc Sabatella · 12-19-2009, 12:58 PM

As mentioned, you need examples in order to get usable advice. But I'll guess anyhow: you're shooting at f/2.8, the camera is focusing on the tip of the nose, and DOF is shallow enough to put most of the rest of the face out of focus. You need to somehow make sure focus is on the eyes. Best way is is to use MF, but if you're lucky, you might be able to get the AF system to choose the eye if you select the focus point yourself and are taking enough of a closeup that the nose isn't within range of the AF sensor.

stianb · 12-20-2009, 08:14 AM

Thanks a lot for your replies. I appreciate that you take the tiime to try to help me.

I've uploaded some examples. The main problem, is that I feel there is a slight blur on all the pictures. I try to adjust it using the sharpening filter in Photoshop, but it's annoying that I have to do that every time and they easily get too pixelated. I am always trying to focus on the eyes.

I'd be happy for any comments on the examples below. I don't know if it can easily be detected. I feel I see the "blur" when I zoom in to 60-70 percent

Flickr Photo Download:

Flickr Photo Download:

Flickr Photo Download: (The error in this photo may have been the shutter speed - 1/90 s)

Ben_Edict · 12-20-2009, 09:22 AM

Originally posted by stianb

Thanks a lot for your replies. I appreciate that you take the tiime to try to help me.

I've uploaded some examples. The main problem, is that I feel there is a slight blur on all the pictures. I try to adjust it using the sharpening filter in Photoshop, but it's annoying that I have to do that every time and they easily get too pixelated. I am always trying to focus on the eyes.

I'd be happy for any comments on the examples below. I don't know if it can easily be detected. I feel I see the "blur" when I zoom in to 60-70 percent

Flickr Photo Download:

Flickr Photo Download:

Flickr Photo Download: (The error in this photo may have been the shutter speed - 1/90 s)

I find all three images acceptably sharp. All of them would stand up to more sharpening in pp, which is a necessity with all digital images anyway.

If you notice the blur at a certain magnification step, it might well be more an issue of screen interpolation, than a real issue with the image.

Ben

kenyee · 12-20-2009, 09:51 AM

looks ok to me as well...you can see the lines on her face. How sharp did you want this? :-P

Marc Sabatella · 12-20-2009, 11:13 AM

In picture #2, it seems the camera probably choose to focus on the hat rather than the face (a perfectly legitimate choice!), and the DOF wasn't quite enough to compensate, but still, that's pretty sharp considering. I'm wondering if you're familiar with the idea of DOF, and are expecting the entire face to be in focus? That's not going to happen at large apertures - the nose and ears won't be in focus at the same time.

stianb · 12-21-2009, 08:04 PM

Thanks a lot for your feedback. Really appreciated. I'll experiment a bit more and take the comments into consideration.

stl_stadtroller · 12-24-2009, 02:21 PM

I'm going to have to go with simple DOF on this too. The beard hairs in pic #3 give a perfect point of refference. Closer ones are sharp fine lines, but hairs just beyond are slightly blurred, getting more so as you go around the face.

Great subjects BTW!

**interested_observer** · 12-26-2009, 11:32 AM

Morning,

I downloaded the first picture and used PhotoME on it to extract the exif metadata. You are using a K20, f 3.5 with a lens using a focal length of 63mm. Went to a DoF calculator at

Online Depth of Field Calculator

and entered the information, guessing the distance to the subject at 5 feet. This resulted in a depth of field of 4". If the distance was 10 feet the DOF would be 1 foot. Not a lot. It really depends on your focus point. It looks close, but its difficult to tell exactly where it is. To open up the depth of field, you would need to stop down some more, to say f5.6 (at 5 feet dof is 5"), f8 (at 5 feet dof is 7"), at f13 (at 5 feet dof is 1 foot). Either that or to back up a bit and increase the distance, but if you zoom in a bit more to say 100mm, you have achieved nothing as the dof goes back down. The best solution is to stop down to around f13 and have a bit more depth of field to get the subject in focus. If you backup some, adding distance, keep the same focal length and then crop to get the image you desire.

All in all, you have a great background and a wonderful picture. The gentleman is really well defined and pulled out (isolated) from the background.

12-18-2009, 03:58 PM	#1
stianb New Member Join Date: Dec 2009 Posts: 6	AF issues with K20D I feel that most of the portraits I take with my K20D is ever so slightly out of focus. I wonder if anyone else has experienced the same problem and if so, if there are any ways to be corrected. I'm using the 50-135 and a 100mm macro lense for portraits. I'm not inclined to believe it's a problem with the photographer anymore, since I've experimented a lot.

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12-18-2009, 04:01 PM	#2
Damn Brit Guest	Welcome to the forum. Examples please with exif data. We can't determine anything from a few words. We're not inclined to believe it's not the photographer without visual evidence because any of us are fallible to missing something, a picture doesn't lie. It is possible that you are getting front or back focus and you can make adjustments on your K20, you'll find details in the manual. If you look around on PentaxForums, you'll find plenty of discussions about the subject. Last edited by Damn Brit; 12-18-2009 at 05:29 PM.

12-18-2009, 05:39 PM	#3
Raybo Veteran Member Join Date: Dec 2007 Posts: 872	I get quite a few OOF images with my K20 and it's mostly due to me.

12-18-2009, 09:58 PM	#4
Ash Community Manager Join Date: Mar 2007 Location: Toowoomba, Queensland Photos: Gallery \| Albums Posts: 23,681	Welcome to the forum. Do post some examples and tell us if it's consistent back or front focusing happening with one, some or all your lenses.

12-18-2009, 10:10 PM	#5
Raybo Veteran Member Join Date: Dec 2007 Posts: 872	I just wish Pentax had a smooth diopter setting instead of the clicky style. My diopter just happens to be on one of in between settings and it's really hard to get it just right.

12-19-2009, 08:04 AM	#6
jolee1990 Forum Member Join Date: Aug 2009 Location: cincinnati Posts: 88	i did too, but i still don't know the reason so i am gonna post some pics up later

12-19-2009, 12:58 PM	#7
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,686	As mentioned, you need examples in order to get usable advice. But I'll guess anyhow: you're shooting at f/2.8, the camera is focusing on the tip of the nose, and DOF is shallow enough to put most of the rest of the face out of focus. You need to somehow make sure focus is on the eyes. Best way is is to use MF, but if you're lucky, you might be able to get the AF system to choose the eye if you select the focus point yourself and are taking enough of a closeup that the nose isn't within range of the AF sensor.

12-20-2009, 08:14 AM	#8
stianb New Member Join Date: Dec 2009 Posts: 6 Original Poster	Thanks a lot for your replies. I appreciate that you take the tiime to try to help me. I've uploaded some examples. The main problem, is that I feel there is a slight blur on all the pictures. I try to adjust it using the sharpening filter in Photoshop, but it's annoying that I have to do that every time and they easily get too pixelated. I am always trying to focus on the eyes. I'd be happy for any comments on the examples below. I don't know if it can easily be detected. I feel I see the "blur" when I zoom in to 60-70 percent Flickr Photo Download: Flickr Photo Download: Flickr Photo Download: (The error in this photo may have been the shutter speed - 1/90 s)

12-20-2009, 09:22 AM	#9
Ben_Edict Veteran Member Join Date: Jul 2007 Location: SouthWest "Regio" Photos: Albums Posts: 3,309	Originally posted by stianb Thanks a lot for your replies. I appreciate that you take the tiime to try to help me. I've uploaded some examples. The main problem, is that I feel there is a slight blur on all the pictures. I try to adjust it using the sharpening filter in Photoshop, but it's annoying that I have to do that every time and they easily get too pixelated. I am always trying to focus on the eyes. I'd be happy for any comments on the examples below. I don't know if it can easily be detected. I feel I see the "blur" when I zoom in to 60-70 percent Flickr Photo Download: Flickr Photo Download: Flickr Photo Download: (The error in this photo may have been the shutter speed - 1/90 s) I find all three images acceptably sharp. All of them would stand up to more sharpening in pp, which is a necessity with all digital images anyway. If you notice the blur at a certain magnification step, it might well be more an issue of screen interpolation, than a real issue with the image. Ben

12-20-2009, 09:51 AM	#10
kenyee Veteran Member Join Date: Mar 2007 Location: Boston, PRofMA Photos: Albums Posts: 3,027	looks ok to me as well...you can see the lines on her face. How sharp did you want this? :-P

12-20-2009, 11:13 AM	#11
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,686	In picture #2, it seems the camera probably choose to focus on the hat rather than the face (a perfectly legitimate choice!), and the DOF wasn't quite enough to compensate, but still, that's pretty sharp considering. I'm wondering if you're familiar with the idea of DOF, and are expecting the entire face to be in focus? That's not going to happen at large apertures - the nose and ears won't be in focus at the same time.

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12-21-2009, 08:04 PM	#12
stianb New Member Join Date: Dec 2009 Posts: 6 Original Poster	Thanks a lot for your feedback. Really appreciated. I'll experiment a bit more and take the comments into consideration.

12-24-2009, 02:21 PM	#13
stl_stadtroller New Member Join Date: Jun 2009 Location: St. Louis MO Posts: 23	I'm going to have to go with simple DOF on this too. The beard hairs in pic #3 give a perfect point of refference. Closer ones are sharp fine lines, but hairs just beyond are slightly blurred, getting more so as you go around the face. Great subjects BTW!

12-26-2009, 11:32 AM	#14
interested_observer Loyal Site Supporter Join Date: Jun 2009 Location: Tumbleweed, Arizona Photos: Gallery \| Albums Posts: 5,536	Morning, I downloaded the first picture and used PhotoME on it to extract the exif metadata. You are using a K20, f 3.5 with a lens using a focal length of 63mm. Went to a DoF calculator at Online Depth of Field Calculator and entered the information, guessing the distance to the subject at 5 feet. This resulted in a depth of field of 4". If the distance was 10 feet the DOF would be 1 foot. Not a lot. It really depends on your focus point. It looks close, but its difficult to tell exactly where it is. To open up the depth of field, you would need to stop down some more, to say f5.6 (at 5 feet dof is 5"), f8 (at 5 feet dof is 7"), at f13 (at 5 feet dof is 1 foot). Either that or to back up a bit and increase the distance, but if you zoom in a bit more to say 100mm, you have achieved nothing as the dof goes back down. The best solution is to stop down to around f13 and have a bit more depth of field to get the subject in focus. If you backup some, adding distance, keep the same focal length and then crop to get the image you desire. All in all, you have a great background and a wonderful picture. The gentleman is really well defined and pulled out (isolated) from the background.