K1 spot focus doesn't always spot focus

peterh337 · 07-14-2018, 12:43 PM

I had this the other day but can't reproduce it right now.

Taking the pic of a plant; the standard sort of thing

The above worked OK, as you can see. But earlier I just could not make it focus. I took the battery out for a few secs, to reset the camera.

Is there some gotcha with the spot focus?

I did have the movable spot location in the middle of the image.

**Mikesul** · 07-14-2018, 02:18 PM

Please give us some more details about your settings and what happened. Sometimes we are too close for the focus to work. If the camera is set to focus priority it will not fire in that circumstance. I offer that as an example. There may well have been some other issue.

C_Jones · 07-14-2018, 02:33 PM

There is a "Hold AF Status" option that you could set to "Off". You can find it in the K-1 manual. It is a camera menu option for AF settings. I myself keep mine off. I do not want anything restricting my shutter release. I am not sure if that not being set to off may be influencing your shooting, but it could possibly.

I also shoot in AF.C most of the time instead of AF.S. The AF.C mode being the one which will not lock after pressing the shutter down halfway, but will adjust, as opposed to AF.S which will lock.

As was already mentioned, you could also be too close for the lens to be making focus. That depends on what the specs of the lens are referring to minimal distance that is required to make a normal focus. If your camera makes the acknowledgment beep when you make focus you will know that it is making successful focus.

**jbinpg** · 07-14-2018, 07:34 PM

I believe the Hold options only come into play in AFC when tracking is enabled. The "shutter action on first frame" options is what controls the shutter release in AFC. With AFS, there is the option which either prevents or allows shutter release if the subject is not in focus.

*MightyMike* · 07-14-2018, 07:44 PM

This is how the focus point size and area coverage actually appear as told to me by a Pentax service tech (I drew this up based on what they explained to me)

peterh337 · 07-14-2018, 10:43 PM - **1 Like**

The distance was well OK for the lens (24-70 f2.8) - distance about 1m.
The config is to not release the shutter until focus is achieved; this is occassionally irritating, indeed.

Most of my photography is landscape so I don't use spot focus; I use the 3x3 option which is the next one up from the spot. This almost totally prevents the shutter release block when there is a low contrast area in the middle (e.g. some calm water).

I have just been out in the garden and cannot make it fail

MightyMike - your diagram suggests that spot focus may not work for vertical or horizontal line objects if they are thinner than about 2x the dot width.

Dericali · 07-15-2018, 02:28 PM

Was it focusing on nothing and hunting or focusing on the background?

As @MightyMike shows in the diagramme above, the AF spots are quite big, and it may focus on the background area if it's higher contrast and in the edges of the 'spot'.

beholder3 · 07-15-2018, 02:53 PM

Originally posted by MightyMike

This is how the focus point size and area coverage actually appear as told to me by a Pentax service tech (I drew this up based on what they explained to me)

That is wrong at least with regards to the distances between vertical lines.

Those are definitely all equal. It can't be different, since the spacing of the actual lines on the sensor module is equidistant: http://www.photographyreview.com/reviews/wp-content/uploads/2013/10/pentax-K...r-1024x766.jpg

*MightyMike* · 07-15-2018, 05:44 PM

Originally posted by beholder3

That is wrong at least with regards to the distances between vertical lines.

Those are definitely all equal. It can't be different, since the spacing of the actual lines on the sensor module is equidistant: http://www.photographyreview.com/reviews/wp-content/uploads/2013/10/pentax-K...r-1024x766.jpg

That is making the assumption that the optics leading to the chip are perfectly symmetrical.

---------- Post added 07-15-18 at 08:45 PM ----------

Originally posted by peterh337

MightyMike - your diagram suggests that spot focus may not work for vertical or horizontal line objects if they are thinner than about 2x the dot width.

You never hold the camera steady or perfectly straight, this is not something to worry about.

peterh337 · 07-15-2018, 11:12 PM

It was focusing on other objects, in the background of the one intended.

With more testing it does just look like the size of the focus spot is just bigger than is shown in the viewfinder.

beholder3 · 07-15-2018, 11:59 PM

Originally posted by MightyMike

That is making the assumption that the optics leading to the chip are perfectly symmetrical.

Well, it is not making your exotic assumption that they use lenses which stretch certain bits of the image, especially in the case of AF, where two images need to be compared pixel by pixel.

Let's let the readers decide which sounds more reasonable.

---------- Post added 16th Jul 2018 at 09:09 ----------

Originally posted by peterh337

it does just look like the size of the focus spot is just bigger than is shown in the viewfinder.

This is always the case, see Canon for example: Canon DLC: Article: An inside look at Spot AF

The user Barry Pearson has a nice image of the focus points and the actual size of the center ("spot") cross, which you can use as overlay image in Lightroom.

Roughly speaking: Draw a square into the spot metering circle of the viewfinder overlay as big as possible with the four corners touching the circle. Then draw a cross sensor inside the square as big as possible.

Dericali · 07-16-2018, 04:34 AM

Originally posted by beholder3

This is always the case, see Canon for example: Canon DLC: Article: An inside look at Spot AF

The user Barry Pearson has a nice image of the focus points and the actual size of the center ("spot") cross, which you can use as overlay image in Lightroom.

Roughly speaking: Draw a square into the spot metering circle of the viewfinder overlay as big as possible with the four corners touching the circle. Then draw a cross sensor inside the square as big as possible.

Is it confirmed that the 'spot' focus mode on the K1 has a different size to the single point 'select' focus mode? E.g. is there any different between spot and SEL mode with selection of the centre point?

peterh337 · 07-16-2018, 04:57 AM

That would be interesting to know too... I did wonder about that.

beholder3 · 07-16-2018, 06:13 AM

Originally posted by Dericali

Is it confirmed that the 'spot' focus mode on the K1 has a different size to the single point 'select' focus mode? E.g. is there any different between spot and SEL mode with selection of the centre point?

No. Canon calls as special small size version of the AF cross "spot", while Pentax calls a fixed center AF field "spot". But that has no impact to my statement or the link. The graphics in the link simply shows that typically the actual cross is significantly larger than the point display in the viewfinder (true for all DSLR systems).

*MightyMike* · 07-16-2018, 07:20 AM

Originally posted by beholder3

Well, it is not making your exotic assumption that they use lenses which stretch certain bits of the image, especially in the case of AF, where two images need to be compared pixel by pixel.

Let's let the readers decide which sounds more reasonable.[COLOR="Silver"]

The corner cross type points were described to me as L-shaped not T-shaped in the orientation I've provided in the image, perhaps the spacing isn't spot on but the orientation certainly is

07-14-2018, 12:43 PM	#1
peterh337 Veteran Member Join Date: Jan 2009 Location: London Posts: 573	K1 spot focus doesn't always spot focus I had this the other day but can't reproduce it right now. Taking the pic of a plant; the standard sort of thing The above worked OK, as you can see. But earlier I just could not make it focus. I took the battery out for a few secs, to reset the camera. Is there some gotcha with the spot focus? I did have the movable spot location in the middle of the image.

07-14-2018, 10:43 PM - 1 Like	#6
peterh337 Veteran Member Join Date: Jan 2009 Location: London Posts: 573 Original Poster	The distance was well OK for the lens (24-70 f2.8) - distance about 1m. The config is to not release the shutter until focus is achieved; this is occassionally irritating, indeed. Most of my photography is landscape so I don't use spot focus; I use the 3x3 option which is the next one up from the spot. This almost totally prevents the shutter release block when there is a low contrast area in the middle (e.g. some calm water). I have just been out in the garden and cannot make it fail MightyMike - your diagram suggests that spot focus may not work for vertical or horizontal line objects if they are thinner than about 2x the dot width. Last edited by peterh337; 07-14-2018 at 11:04 PM.

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07-14-2018, 02:18 PM	#2
Mikesul Loyal Site Supporter Join Date: Sep 2009 Location: Phoenix, AZ Posts: 7,594	Please give us some more details about your settings and what happened. Sometimes we are too close for the focus to work. If the camera is set to focus priority it will not fire in that circumstance. I offer that as an example. There may well have been some other issue.

07-14-2018, 02:33 PM	#3
C_Jones Pentaxian Join Date: Sep 2012 Location: NY Photos: Gallery \| Albums Posts: 6,079	There is a "Hold AF Status" option that you could set to "Off". You can find it in the K-1 manual. It is a camera menu option for AF settings. I myself keep mine off. I do not want anything restricting my shutter release. I am not sure if that not being set to off may be influencing your shooting, but it could possibly. I also shoot in AF.C most of the time instead of AF.S. The AF.C mode being the one which will not lock after pressing the shutter down halfway, but will adjust, as opposed to AF.S which will lock. As was already mentioned, you could also be too close for the lens to be making focus. That depends on what the specs of the lens are referring to minimal distance that is required to make a normal focus. If your camera makes the acknowledgment beep when you make focus you will know that it is making successful focus.

07-14-2018, 07:34 PM	#4
jbinpg Site Supporter Join Date: Mar 2008 Location: Prince George, BC Photos: Gallery \| Albums Posts: 3,546	I believe the Hold options only come into play in AFC when tracking is enabled. The "shutter action on first frame" options is what controls the shutter release in AFC. With AFS, there is the option which either prevents or allows shutter release if the subject is not in focus.

07-14-2018, 07:44 PM	#5
MightyMike Marketplace Reseller Join Date: Nov 2008 Location: Canada Posts: 9,320	This is how the focus point size and area coverage actually appear as told to me by a Pentax service tech (I drew this up based on what they explained to me)

07-15-2018, 02:28 PM	#7
Dericali Senior Member Join Date: Jul 2016 Location: Berlin Posts: 298	Was it focusing on nothing and hunting or focusing on the background? As @MightyMike shows in the diagramme above, the AF spots are quite big, and it may focus on the background area if it's higher contrast and in the edges of the 'spot'.

07-15-2018, 02:53 PM	#8
beholder3 Pentaxian Join Date: Dec 2011 Posts: 3,112	Originally posted by MightyMike This is how the focus point size and area coverage actually appear as told to me by a Pentax service tech (I drew this up based on what they explained to me) That is wrong at least with regards to the distances between vertical lines. Those are definitely all equal. It can't be different, since the spacing of the actual lines on the sensor module is equidistant: http://www.photographyreview.com/reviews/wp-content/uploads/2013/10/pentax-K...r-1024x766.jpg

07-15-2018, 05:44 PM	#9
MightyMike Marketplace Reseller Join Date: Nov 2008 Location: Canada Posts: 9,320	Originally posted by beholder3 That is wrong at least with regards to the distances between vertical lines. Those are definitely all equal. It can't be different, since the spacing of the actual lines on the sensor module is equidistant: http://www.photographyreview.com/reviews/wp-content/uploads/2013/10/pentax-K...r-1024x766.jpg That is making the assumption that the optics leading to the chip are perfectly symmetrical. ---------- Post added 07-15-18 at 08:45 PM ---------- Originally posted by peterh337 MightyMike - your diagram suggests that spot focus may not work for vertical or horizontal line objects if they are thinner than about 2x the dot width. You never hold the camera steady or perfectly straight, this is not something to worry about.

07-15-2018, 11:12 PM	#10
peterh337 Veteran Member Join Date: Jan 2009 Location: London Posts: 573 Original Poster	It was focusing on other objects, in the background of the one intended. With more testing it does just look like the size of the focus spot is just bigger than is shown in the viewfinder.

07-15-2018, 11:59 PM	#11
beholder3 Pentaxian Join Date: Dec 2011 Posts: 3,112	Originally posted by MightyMike That is making the assumption that the optics leading to the chip are perfectly symmetrical. Well, it is not making your exotic assumption that they use lenses which stretch certain bits of the image, especially in the case of AF, where two images need to be compared pixel by pixel. Let's let the readers decide which sounds more reasonable. ---------- Post added 16th Jul 2018 at 09:09 ---------- Originally posted by peterh337 it does just look like the size of the focus spot is just bigger than is shown in the viewfinder. This is always the case, see Canon for example: Canon DLC: Article: An inside look at Spot AF The user Barry Pearson has a nice image of the focus points and the actual size of the center ("spot") cross, which you can use as overlay image in Lightroom. Roughly speaking: Draw a square into the spot metering circle of the viewfinder overlay as big as possible with the four corners touching the circle. Then draw a cross sensor inside the square as big as possible.

07-16-2018, 04:34 AM	#12
Dericali Senior Member Join Date: Jul 2016 Location: Berlin Posts: 298	Originally posted by beholder3 This is always the case, see Canon for example: Canon DLC: Article: An inside look at Spot AF The user Barry Pearson has a nice image of the focus points and the actual size of the center ("spot") cross, which you can use as overlay image in Lightroom. Roughly speaking: Draw a square into the spot metering circle of the viewfinder overlay as big as possible with the four corners touching the circle. Then draw a cross sensor inside the square as big as possible. Is it confirmed that the 'spot' focus mode on the K1 has a different size to the single point 'select' focus mode? E.g. is there any different between spot and SEL mode with selection of the centre point?

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07-16-2018, 04:57 AM	#13
peterh337 Veteran Member Join Date: Jan 2009 Location: London Posts: 573 Original Poster	That would be interesting to know too... I did wonder about that.

07-16-2018, 06:13 AM	#14
beholder3 Pentaxian Join Date: Dec 2011 Posts: 3,112	Originally posted by Dericali Is it confirmed that the 'spot' focus mode on the K1 has a different size to the single point 'select' focus mode? E.g. is there any different between spot and SEL mode with selection of the centre point? No. Canon calls as special small size version of the AF cross "spot", while Pentax calls a fixed center AF field "spot". But that has no impact to my statement or the link. The graphics in the link simply shows that typically the actual cross is significantly larger than the point display in the viewfinder (true for all DSLR systems).

07-16-2018, 07:20 AM	#15
MightyMike Marketplace Reseller Join Date: Nov 2008 Location: Canada Posts: 9,320	Originally posted by beholder3 Well, it is not making your exotic assumption that they use lenses which stretch certain bits of the image, especially in the case of AF, where two images need to be compared pixel by pixel. Let's let the readers decide which sounds more reasonable.[COLOR="Silver"] The corner cross type points were described to me as L-shaped not T-shaped in the orientation I've provided in the image, perhaps the spacing isn't spot on but the orientation certainly is