K-x Sharpness problem

**firefly** · 02-28-2010, 08:40 PM

Not to get too off topic, but I just came upon this while googling about k-x AF adjustment. It's a spec sheet and appears to be released by Pentax (it has all the correct part numbers on it). On page 2, under the 'Others' features sections, it mentions per lens adjustment. I wonder if there is some possible ability there, just not implemented in firmware?

dragonfly · 02-28-2010, 08:50 PM

I have found that my kit lens isn't as sharp as prime lenses that I've been able to buy to replace it.

alaskaguy · 02-28-2010, 10:02 PM

mine is in the mail...is it likely that i will have to do this, or is it a somewhat rare problem??

**firefly** · 03-01-2010, 06:04 AM

I'd say it's extremely common. However, it's usually off by such a minute amount that people generally don't even notice.

Originally posted by alaskaguy

mine is in the mail...is it likely that i will have to do this, or is it a somewhat rare problem??

Marc Sabatella · 03-01-2010, 08:50 AM

Before rushing to figure out the hacks necessary to calibrate focus, first rule out the more conventional causes of blur:

1) Camera didn't focus where you thought it. I see a circle where you wanted the camera to focus; presumably you selected the focus point manually. But are you aware the focus sensor is pretty broad, and might have focused somewhere else "near" the selected point? Any chance that this led to the camera choosing to focus a little in front of where you intended?

2) You used a tripod, but how sturdy of a tripod, and did you use the two-second timer to engage the mirror lockup? The mirror slap on a DSLR requires a pretty sturdy tripod and the use of MLU (and liveview kind of gives you that already).

Hemi345 · 03-01-2010, 09:15 AM

Try switching the LV focus mode to Phase to see if the images look similar to non-LV.

coley fillet · 03-02-2010, 02:46 AM

Originally posted by Marc Sabatella

Before rushing to figure out the hacks necessary to calibrate focus, first rule out the more conventional causes of blur:

1) Camera didn't focus where you thought it. I see a circle where you wanted the camera to focus; presumably you selected the focus point manually. But are you aware the focus sensor is pretty broad, and might have focused somewhere else "near" the selected point? Any chance that this led to the camera choosing to focus a little in front of where you intended?

2) You used a tripod, but how sturdy of a tripod, and did you use the two-second timer to engage the mirror lockup? The mirror slap on a DSLR requires a pretty sturdy tripod and the use of MLU (and liveview kind of gives you that already).

Hi Marc,

My tripod is very sturdy and I used a 2 second delay with both shots.

I just tested the camera again focussing on newspaper text at a 45 degree angle and found that the Tamron back focussed (by two lines of text) and the kit lens front focussed (by two lines of text) using the K-x's conventional phase auto focus. Both lenses focus exactly where I want when used with the Live view contrast focus and interestingly both lenses mis-focus again when using Live view phase focus. So I'm guessing that the cameras phase focus system is faulty.

sterretje · 03-02-2010, 03:04 AM

Not faulty but needs adjustment. Go back to the shop and let them fix it or let them give you a better camera. Take all your lenses with. Similar to other models, I assume that the KX can be calibrated for a number of lenses. That however can only be done by Pentax and they will usually not calibrate for 3rd party lenses.
Maybe you can ask them to do default calibration for Tamron and add offsets for other lenses; not sure if it's possible.

Good luck, whatever you decide to do.

coley fillet · 03-02-2010, 11:54 AM

I originally bought the camera from an on-line store and sent it back today, I may decide to go for body only this time as I don't think I'll be using the kit lens.

**firefly** · 03-02-2010, 12:16 PM

Originally posted by coley fillet

I just tested the camera again focussing on newspaper text at a 45 degree angle and found that the Tamron back focussed (by two lines of text) and the kit lens front focussed (by two lines of text) using the K-x's conventional phase auto focus. Both lenses focus exactly where I want when used with the Live view contrast focus and interestingly both lenses mis-focus again when using Live view phase focus. So I'm guessing that the cameras phase focus system is faulty.

I would not use a 45 degree target. Using a 45 ruler alongside a vertical target is fine, as this would give you an idea of whether you are front or back focused.

Always use high contrast target that is parallel to your cameras sensor on all axes.

Marc Sabatella · 03-02-2010, 01:51 PM

Originally posted by coley fillet

I just tested the camera again focussing on newspaper text at a 45 degree angle and found that the Tamron back focussed (by two lines of text) and the kit lens front focussed (by two lines of text) using the K-x's conventional phase auto focus

You can't test focus using a newspaper in this way - the focus sensors used in traditional phase-detect AF are much larger than a single line of text. So you might aim the selected focus point at one line of text, but the camera might legitimately choose to focus a couple of lines in front or in back because those are still within range of the focus sensor. That's why focus test charts exist - to provide an unambiguous target.

coley fillet · 03-05-2010, 02:43 AM

Just had a call from the online camera store I bought my K-x from and they have comfirmed that the camera had an auto-focus problem and they will be sending it, along with other faulty K-x's back to Pentax. He said that they had a faulty batch and Pentax had recalled them. I am now waiting for a body only (black) replacement which I should get by Monday.

**firefly** · 03-05-2010, 07:23 AM

Interesting that Pentax had recalled a batch. Could be that many made in to the wild, and could account for a good deal of k-x issues we are hearing about.

GeneV · 03-05-2010, 07:52 AM

That should get us all furiously checking our K-x bodies.

twokatmew · 03-05-2010, 08:13 AM

Originally posted by GeneV

That should get us all furiously checking our K-x bodies.

It would be nice if Pentax would post the serial numbers on their support site. Who knows if B&H (or other online vendors) will notify us if our cameras are affected. I suppose though, that if any online vendors do, B&H will be one of them.

I guess I won't worry though, because even at F1.4, my K-x seems to be focusing just fine.

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02-28-2010, 08:40 PM	#16
firefly Site Supporter Join Date: Mar 2008 Location: New Brunswick Photos: Albums Posts: 200	Not to get too off topic, but I just came upon this while googling about k-x AF adjustment. It's a spec sheet and appears to be released by Pentax (it has all the correct part numbers on it). On page 2, under the 'Others' features sections, it mentions per lens adjustment. I wonder if there is some possible ability there, just not implemented in firmware?

02-28-2010, 08:50 PM	#17
dragonfly Veteran Member Join Date: Jun 2009 Location: on the wall Photos: Gallery Posts: 715	I have found that my kit lens isn't as sharp as prime lenses that I've been able to buy to replace it.

02-28-2010, 10:02 PM	#18
alaskaguy Inactive Account Join Date: Feb 2010 Location: Anchorage,AK Posts: 21	mine is in the mail...is it likely that i will have to do this, or is it a somewhat rare problem??

03-01-2010, 06:04 AM	#19
firefly Site Supporter Join Date: Mar 2008 Location: New Brunswick Photos: Albums Posts: 200	I'd say it's extremely common. However, it's usually off by such a minute amount that people generally don't even notice. Originally posted by alaskaguy mine is in the mail...is it likely that i will have to do this, or is it a somewhat rare problem??

03-01-2010, 08:50 AM	#20
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,685	Before rushing to figure out the hacks necessary to calibrate focus, first rule out the more conventional causes of blur: 1) Camera didn't focus where you thought it. I see a circle where you wanted the camera to focus; presumably you selected the focus point manually. But are you aware the focus sensor is pretty broad, and might have focused somewhere else "near" the selected point? Any chance that this led to the camera choosing to focus a little in front of where you intended? 2) You used a tripod, but how sturdy of a tripod, and did you use the two-second timer to engage the mirror lockup? The mirror slap on a DSLR requires a pretty sturdy tripod and the use of MLU (and liveview kind of gives you that already).

03-01-2010, 09:15 AM	#21
Hemi345 Senior Member Join Date: Jan 2010 Location: Colorado Posts: 127	Try switching the LV focus mode to Phase to see if the images look similar to non-LV.

03-02-2010, 02:46 AM	#22
coley fillet New Member Join Date: Feb 2010 Posts: 8 Original Poster	Originally posted by Marc Sabatella Before rushing to figure out the hacks necessary to calibrate focus, first rule out the more conventional causes of blur: 1) Camera didn't focus where you thought it. I see a circle where you wanted the camera to focus; presumably you selected the focus point manually. But are you aware the focus sensor is pretty broad, and might have focused somewhere else "near" the selected point? Any chance that this led to the camera choosing to focus a little in front of where you intended? 2) You used a tripod, but how sturdy of a tripod, and did you use the two-second timer to engage the mirror lockup? The mirror slap on a DSLR requires a pretty sturdy tripod and the use of MLU (and liveview kind of gives you that already). Hi Marc, My tripod is very sturdy and I used a 2 second delay with both shots. I just tested the camera again focussing on newspaper text at a 45 degree angle and found that the Tamron back focussed (by two lines of text) and the kit lens front focussed (by two lines of text) using the K-x's conventional phase auto focus. Both lenses focus exactly where I want when used with the Live view contrast focus and interestingly both lenses mis-focus again when using Live view phase focus. So I'm guessing that the cameras phase focus system is faulty.

03-02-2010, 03:04 AM	#23
sterretje Veteran Member Join Date: Dec 2008 Location: Roodepoort, South Africa Photos: Gallery \| Albums Posts: 3,561	Not faulty but needs adjustment. Go back to the shop and let them fix it or let them give you a better camera. Take all your lenses with. Similar to other models, I assume that the KX can be calibrated for a number of lenses. That however can only be done by Pentax and they will usually not calibrate for 3rd party lenses. Maybe you can ask them to do default calibration for Tamron and add offsets for other lenses; not sure if it's possible. Good luck, whatever you decide to do.

03-02-2010, 11:54 AM	#24
coley fillet New Member Join Date: Feb 2010 Posts: 8 Original Poster	I originally bought the camera from an on-line store and sent it back today, I may decide to go for body only this time as I don't think I'll be using the kit lens.

03-02-2010, 12:16 PM	#25
firefly Site Supporter Join Date: Mar 2008 Location: New Brunswick Photos: Albums Posts: 200	Originally posted by coley fillet I just tested the camera again focussing on newspaper text at a 45 degree angle and found that the Tamron back focussed (by two lines of text) and the kit lens front focussed (by two lines of text) using the K-x's conventional phase auto focus. Both lenses focus exactly where I want when used with the Live view contrast focus and interestingly both lenses mis-focus again when using Live view phase focus. So I'm guessing that the cameras phase focus system is faulty. I would not use a 45 degree target. Using a 45 ruler alongside a vertical target is fine, as this would give you an idea of whether you are front or back focused. Always use high contrast target that is parallel to your cameras sensor on all axes.

03-02-2010, 01:51 PM	#26
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,685	Originally posted by coley fillet I just tested the camera again focussing on newspaper text at a 45 degree angle and found that the Tamron back focussed (by two lines of text) and the kit lens front focussed (by two lines of text) using the K-x's conventional phase auto focus You can't test focus using a newspaper in this way - the focus sensors used in traditional phase-detect AF are much larger than a single line of text. So you might aim the selected focus point at one line of text, but the camera might legitimately choose to focus a couple of lines in front or in back because those are still within range of the focus sensor. That's why focus test charts exist - to provide an unambiguous target.

03-05-2010, 02:43 AM	#27
coley fillet New Member Join Date: Feb 2010 Posts: 8 Original Poster	Just had a call from the online camera store I bought my K-x from and they have comfirmed that the camera had an auto-focus problem and they will be sending it, along with other faulty K-x's back to Pentax. He said that they had a faulty batch and Pentax had recalled them. I am now waiting for a body only (black) replacement which I should get by Monday.

03-05-2010, 07:23 AM	#28
firefly Site Supporter Join Date: Mar 2008 Location: New Brunswick Photos: Albums Posts: 200	Interesting that Pentax had recalled a batch. Could be that many made in to the wild, and could account for a good deal of k-x issues we are hearing about.

03-05-2010, 07:52 AM	#29
GeneV Veteran Member Join Date: Oct 2008 Location: Albuquerque NM Photos: Albums Posts: 9,830	That should get us all furiously checking our K-x bodies.

03-05-2010, 08:13 AM	#30
twokatmew Veteran Member Join Date: Jan 2010 Location: Lansing, MI Photos: Albums Posts: 509	Originally posted by GeneV That should get us all furiously checking our K-x bodies. It would be nice if Pentax would post the serial numbers on their support site. Who knows if B&H (or other online vendors) will notify us if our cameras are affected. I suppose though, that if any online vendors do, B&H will be one of them. I guess I won't worry though, because even at F1.4, my K-x seems to be focusing just fine.