All the fuss about AF point size

Giklab · 03-04-2012, 07:27 AM

Originally posted by Giklab

Come to think about it, it's mostly professional cameras that show AF points for what they really are.

Seems I phrased this wrong, forget the professional part:

Some cameras have focus indicators that really show the size of the AF point, and they were mostly found in the higher-priced market.

I'm still all right in my head and didn't mean to troll or anything. It's just that it annoys me that people hate on the issue when the answer is (literally) in front of their noses.
It doesn't change the fact that the point is big, but it's not as huge as you'd be inclined to think if you read some posts (in other threads).

telly0050 · 03-04-2012, 08:45 AM

thanks that's really informative.

just a thought, since the center AF is larger than we need, does other AF points have a "point" focus area?
maybe we can just use 1 of the 8 points within the square to "replace" the center AF point?

kenyee · 03-04-2012, 09:36 AM

Originally posted by telly0050

just a thought, since the center AF is larger than we need, does other AF points have a "point" focus area?
maybe we can just use 1 of the 8 points within the square to "replace" the center AF point?

They're not as large, but they're still bigger than the AF point indicates. To make it worse, the AF point indicators can be slightly off center. Best thing to do is the AF point measurement exercise I mentioned before to figure out where your AF points are...

westmill · 03-04-2012, 11:37 AM

Originally posted by telly0050

thanks that's really informative.

just a thought, since the center AF is larger than we need, does other AF points have a "point" focus area?
maybe we can just use 1 of the 8 points within the square to "replace" the center AF point?

No... Im afraid they are all the same size.
If you look at the map Giklab posted you can draw pretty much imaginary lines and there would be a bit
of a gap between each point. Not all the points are
cross hair either as someone has already mentioned.
I think its better to use the centre simply because at
least you now know that its acurately lined to the semicircles !

alohadave · 03-04-2012, 12:06 PM

Originally posted by westmill

What it is, is that most cameras, the focus point is the red square itself. in the K5 the autofocus square does indeed stretch to the idicated semicircles !
This simply meens the the autofocus point is indeed quite large. Anyone beleiving the focus point is just the red square will get an awful lot of focus errors !

On most cameras the focus indicator simply tells you which AF point has grabbed focus. It doesn't specifically mean that the area inside the red square is where the exact point of focus is.

The AF sensors are below the mirror in the lightbox, and the AF indicators are projected onto the focusing screen. They don't necessarily align where you see the red box.

westmill · 03-04-2012, 01:40 PM

Thats correct but even though its not the actual indicator they are normily fairly close and Ive noticed in some cameras that the focus indicators vary in size too.
Which kind of tells me the camera companys try to get it right. I must admit that the Nikons seem to be smaller than most, but as small as they are they are
spot on. Ive only ever owned one camera that wasnt a top end job which was a minolta though, but even that seemed pretty accurate.
Other than that i think this thread has made the same point crystal clear by now.

Tommot1965 · 03-04-2012, 04:09 PM

Originally posted by westmill

Ive not downloaded it yet, so I would be intrested to see if there are anymore improvements as there was in 1.12.
It has to be physicaly imposs to make the sensors smaller with firmware though so I cant see it will solve much there

I did another model shoot today and another 300+ pics with no oophs. Lots are not as sharp on the eyes where I want but all are usable.
Ive racked my head for a workaround, but I cant see one. One thing that I have thought about is that maybe a pentax lens would have been
better than the tamron because of the ability of manual focusing in Single Shot AF.
Just a thought for you.... but in your case you could try multi point CF ! Im thinking it is more Likely to pick up on the movement
behind the mic etc. Not sure... but it sounds reasonable !

surely more DOF would get you out of jail...if your trying for really critical focusing and very shallow DOF..use either your D300 or the D3s....But I cant understand why your using anything other than the D3s anyway..its probably the best DSLR ever made up until the D4 release...!!

westmill · 03-04-2012, 05:57 PM

Originally posted by Tommot1965

surely more DOF would get you out of jail...if your trying for really critical focusing and very shallow DOF..use either your D300 or the D3s....But I cant understand why your using anything other than the D3s anyway..its probably the best DSLR ever made up until the D4 release...!!

I use different cameras for different things. Horses for courses as they say lol
In the studio or low ISO there is no differance in image quality between the D3s and D300.
The K5 i bought mainly for the high ISO ability. When the K5 gets it right it produces even higher image quality than the D3s.
Well.... as good anyway lol. I genraly prefer APSC to full frame. The APSC gives you that extra DOF and more quality than I need.
Even when im covering the horse racing that 80-200 becomes a 120-300 F2.8 on the D300.
When the light drops I switch over. Also I often use more than one camera with setups using remote trigering.
The K5 is a camera that in many ways has the best of both of these cameras.
There are many reasons for using different cameras. Another strong reason for me is simple usage..... On an average wk I would say
I prob take in order of 2000 pics. The K5 sensor is superb. I agree too that the D4 is prob the best camera on the planet.... but look at that price !
You could buy 8 K5s for that money lol. Yes its good.... but not that good I could never warrant spending that kind of money.
My biggest brunt of work is in the studio. It looks like the K5 is starting to do Ok there.
Also... in the hand I prefer the K5 ! I love it.
I also admit to loving cameras in genral too ! Im seriously thinking of buying the new Fuji Prox1 along with the three current lenses.
I could argue for outdoor use or even weddings or sumit.... truth is though.... it makes me droole lol.
Poss a hang over from my beloved Bronica RF645 and its three lenses.

Tommot1965 · 03-04-2012, 08:28 PM

fair enough.....

I was using a K7 the other day...and after using my D300s I can see the attraction ...

I had two K5s...but they suffered the dreaded FF in low light..so I left the pentax camp...but if a k5 came along with a FA 77 in good light Id be well happy with it

jmg257 · 03-04-2012, 08:32 PM

Originally posted by Giklab

Everybody sais that the AF points are so much larger than indicated. In a thread (that I read recently but cannot find at the moment, would appreciate if somebody points me there) it was found that the center AF point was larger than the one in the VF. That it was about as large as the half-circles in the VF. Hello? NOT INDICATED?

I think it can be seen quite clearly that the AF points are very well indicated. Just overlay the ( ) over any point and you can see it corresponds to the square bracket pattern on the VF.

//rant mode off

If those points are 'well indicated', it is not by the ( ) semi-circle...which is stated as being the "spot metering frame". The af points shown and discussed in the manual, within the specified af frame, give the impression that the actual sensors are rather small. Good and important info to know they are not....thanks for pointing it out how big they actually are!

**MSL** · 03-05-2012, 12:54 PM

Originally posted by Winder

My second biggest complaint about Pentax AF is the golf ball sized center AF point. When shooting singers and musicians I have found the AF locked on to the microphone in front of the face even though it was outside of the center circle. When I tested it I found the center AF point was slightly bigger than the center circle and would grab high contrast objects on the edge before it would focus in the center. Now that I understand how big it is I can work around it, but it does slow me down at times.

I think a number of the mis-shots I had yesterday were due to the camera focusing on the wrong spot. For better or for worse, almost all the the shots I took were using center point focusing, and I can see where it must have been locking onto something a fair distance from the center. But even if I'm wrong, and it was all my own errors, knowing that this center spot has issues, what suggestions do you have for ways to work around it?

JinDesu · 03-05-2012, 01:02 PM

Just jumping in here to ask a question -

From what I'm reading here, it is trying to say that the center point AF sensor (and I assume the rest of them) are quite large (as large as the center circle) and hence people who were expecting to focus on an object within that circle were highly disappointed when the sensor decided to pick up something else.

Now, how does this help us (besides knowledge being power)? Is a larger AF sensor more detrimental? When I to center AF, I generally want that little cross (t) to be my guide. Having the big circle could suck, if my target is smaller than the circle, right? What techniques can be used to give us that little bit more edge when dealing with a bigger AF sensor?

Or am I talking out of my ass here, since this thread moved so fast from "the center AF point is big" to "OH MY GOD IT ALL MAKES SENSE NOW"....

westmill · 03-05-2012, 01:30 PM

Originally posted by JinDesu

Just jumping in here to ask a question -

From what I'm reading here, it is trying to say that the center point AF sensor (and I assume the rest of them) are quite large (as large as the center circle) and hence people who were expecting to focus on an object within that circle were highly disappointed when the sensor decided to pick up something else.

Now, how does this help us (besides knowledge being power)? Is a larger AF sensor more detrimental? When I to center AF, I generally want that little cross (t) to be my guide. Having the big circle could suck, if my target is smaller than the circle, right? What techniques can be used to give us that little bit more edge when dealing with a bigger AF sensor?

Or am I talking out of my ass here, since this thread moved so fast from "the center AF point is big" to "OH MY GOD IT ALL MAKES SENSE NOW"....

Errrrrrr Nope... you got it wrong lol

JinDesu · 03-05-2012, 01:32 PM

Originally posted by westmill

Errrrrrr Nope... you got it wrong lol

oof! Well I sort of figured, but it was a start to get more explanation!

So bigger AF points = better? Or what is it?

westmill · 03-05-2012, 01:39 PM

Originally posted by JinDesu

oof! Well I sort of figured, but it was a start to get more explanation!

So bigger AF points = better? Or what is it?

It would be easier for you to read the first page that explains it quite well.
rather than me or anyone going through it all over again lol. Certainly not better and prob worth reading matey

03-04-2012, 08:32 PM	#40
jmg257 Inactive Account Join Date: Jan 2012 Posts: 202	Originally posted by Giklab Everybody sais that the AF points are so much larger than indicated. In a thread (that I read recently but cannot find at the moment, would appreciate if somebody points me there) it was found that the center AF point was larger than the one in the VF. That it was about as large as the half-circles in the VF. Hello? NOT INDICATED? I think it can be seen quite clearly that the AF points are very well indicated. Just overlay the ( ) over any point and you can see it corresponds to the square bracket pattern on the VF. //rant mode off If those points are 'well indicated', it is not by the ( ) semi-circle...which is stated as being the "spot metering frame". The af points shown and discussed in the manual, within the specified af frame, give the impression that the actual sensors are rather small. Good and important info to know they are not....thanks for pointing it out how big they actually are! Last edited by jmg257; 03-04-2012 at 08:40 PM.

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03-04-2012, 07:27 AM	#31
Giklab Veteran Member Join Date: Jan 2012 Location: Slovenia Photos: Gallery Posts: 2,182 Original Poster	Originally posted by Giklab Come to think about it, it's mostly professional cameras that show AF points for what they really are. Seems I phrased this wrong, forget the professional part: Some cameras have focus indicators that really show the size of the AF point, and they were mostly found in the higher-priced market. I'm still all right in my head and didn't mean to troll or anything. It's just that it annoys me that people hate on the issue when the answer is (literally) in front of their noses. It doesn't change the fact that the point is big, but it's not as huge as you'd be inclined to think if you read some posts (in other threads).

03-04-2012, 08:45 AM	#32
telly0050 Senior Member Join Date: May 2011 Posts: 233	thanks that's really informative. just a thought, since the center AF is larger than we need, does other AF points have a "point" focus area? maybe we can just use 1 of the 8 points within the square to "replace" the center AF point?

03-04-2012, 09:36 AM	#33
kenyee Veteran Member Join Date: Mar 2007 Location: Boston, PRofMA Photos: Albums Posts: 3,026	Originally posted by telly0050 just a thought, since the center AF is larger than we need, does other AF points have a "point" focus area? maybe we can just use 1 of the 8 points within the square to "replace" the center AF point? They're not as large, but they're still bigger than the AF point indicates. To make it worse, the AF point indicators can be slightly off center. Best thing to do is the AF point measurement exercise I mentioned before to figure out where your AF points are...

03-04-2012, 11:37 AM	#34
westmill Veteran Member Join Date: Jan 2012 Location: Stoke on Trent Photos: Gallery \| Albums Posts: 1,146	Originally posted by telly0050 thanks that's really informative. just a thought, since the center AF is larger than we need, does other AF points have a "point" focus area? maybe we can just use 1 of the 8 points within the square to "replace" the center AF point? No... Im afraid they are all the same size. If you look at the map Giklab posted you can draw pretty much imaginary lines and there would be a bit of a gap between each point. Not all the points are cross hair either as someone has already mentioned. I think its better to use the centre simply because at least you now know that its acurately lined to the semicircles !

03-04-2012, 12:06 PM	#35
alohadave Veteran Member Join Date: Jan 2008 Location: Quincy, MA Photos: Gallery \| Albums Posts: 2,024	Originally posted by westmill What it is, is that most cameras, the focus point is the red square itself. in the K5 the autofocus square does indeed stretch to the idicated semicircles ! This simply meens the the autofocus point is indeed quite large. Anyone beleiving the focus point is just the red square will get an awful lot of focus errors ! On most cameras the focus indicator simply tells you which AF point has grabbed focus. It doesn't specifically mean that the area inside the red square is where the exact point of focus is. The AF sensors are below the mirror in the lightbox, and the AF indicators are projected onto the focusing screen. They don't necessarily align where you see the red box.

03-04-2012, 01:40 PM	#36
westmill Veteran Member Join Date: Jan 2012 Location: Stoke on Trent Photos: Gallery \| Albums Posts: 1,146	Thats correct but even though its not the actual indicator they are normily fairly close and Ive noticed in some cameras that the focus indicators vary in size too. Which kind of tells me the camera companys try to get it right. I must admit that the Nikons seem to be smaller than most, but as small as they are they are spot on. Ive only ever owned one camera that wasnt a top end job which was a minolta though, but even that seemed pretty accurate. Other than that i think this thread has made the same point crystal clear by now.

03-04-2012, 04:09 PM	#37
Tommot1965 Veteran Member Join Date: Sep 2010 Location: Perth Western Australia Photos: Gallery \| Albums Posts: 1,026	Originally posted by westmill Ive not downloaded it yet, so I would be intrested to see if there are anymore improvements as there was in 1.12. It has to be physicaly imposs to make the sensors smaller with firmware though so I cant see it will solve much there I did another model shoot today and another 300+ pics with no oophs. Lots are not as sharp on the eyes where I want but all are usable. Ive racked my head for a workaround, but I cant see one. One thing that I have thought about is that maybe a pentax lens would have been better than the tamron because of the ability of manual focusing in Single Shot AF. Just a thought for you.... but in your case you could try multi point CF ! Im thinking it is more Likely to pick up on the movement behind the mic etc. Not sure... but it sounds reasonable ! surely more DOF would get you out of jail...if your trying for really critical focusing and very shallow DOF..use either your D300 or the D3s....But I cant understand why your using anything other than the D3s anyway..its probably the best DSLR ever made up until the D4 release...!!

03-04-2012, 05:57 PM	#38
westmill Veteran Member Join Date: Jan 2012 Location: Stoke on Trent Photos: Gallery \| Albums Posts: 1,146	Originally posted by Tommot1965 surely more DOF would get you out of jail...if your trying for really critical focusing and very shallow DOF..use either your D300 or the D3s....But I cant understand why your using anything other than the D3s anyway..its probably the best DSLR ever made up until the D4 release...!! I use different cameras for different things. Horses for courses as they say lol In the studio or low ISO there is no differance in image quality between the D3s and D300. The K5 i bought mainly for the high ISO ability. When the K5 gets it right it produces even higher image quality than the D3s. Well.... as good anyway lol. I genraly prefer APSC to full frame. The APSC gives you that extra DOF and more quality than I need. Even when im covering the horse racing that 80-200 becomes a 120-300 F2.8 on the D300. When the light drops I switch over. Also I often use more than one camera with setups using remote trigering. The K5 is a camera that in many ways has the best of both of these cameras. There are many reasons for using different cameras. Another strong reason for me is simple usage..... On an average wk I would say I prob take in order of 2000 pics. The K5 sensor is superb. I agree too that the D4 is prob the best camera on the planet.... but look at that price ! You could buy 8 K5s for that money lol. Yes its good.... but not that good I could never warrant spending that kind of money. My biggest brunt of work is in the studio. It looks like the K5 is starting to do Ok there. Also... in the hand I prefer the K5 ! I love it. I also admit to loving cameras in genral too ! Im seriously thinking of buying the new Fuji Prox1 along with the three current lenses. I could argue for outdoor use or even weddings or sumit.... truth is though.... it makes me droole lol. Poss a hang over from my beloved Bronica RF645 and its three lenses.

03-04-2012, 08:28 PM	#39
Tommot1965 Veteran Member Join Date: Sep 2010 Location: Perth Western Australia Photos: Gallery \| Albums Posts: 1,026	fair enough..... I was using a K7 the other day...and after using my D300s I can see the attraction ... I had two K5s...but they suffered the dreaded FF in low light..so I left the pentax camp...but if a k5 came along with a FA 77 in good light Id be well happy with it

03-05-2012, 12:54 PM	#41
MSL Site Supporter Join Date: Feb 2012 Location: Greater Toronto Area Photos: Gallery \| Albums Posts: 4,749	Originally posted by Winder My second biggest complaint about Pentax AF is the golf ball sized center AF point. When shooting singers and musicians I have found the AF locked on to the microphone in front of the face even though it was outside of the center circle. When I tested it I found the center AF point was slightly bigger than the center circle and would grab high contrast objects on the edge before it would focus in the center. Now that I understand how big it is I can work around it, but it does slow me down at times. I think a number of the mis-shots I had yesterday were due to the camera focusing on the wrong spot. For better or for worse, almost all the the shots I took were using center point focusing, and I can see where it must have been locking onto something a fair distance from the center. But even if I'm wrong, and it was all my own errors, knowing that this center spot has issues, what suggestions do you have for ways to work around it?

03-05-2012, 01:02 PM	#42
JinDesu Veteran Member Join Date: Jun 2011 Location: New York City Photos: Gallery Posts: 5,638	Just jumping in here to ask a question - From what I'm reading here, it is trying to say that the center point AF sensor (and I assume the rest of them) are quite large (as large as the center circle) and hence people who were expecting to focus on an object within that circle were highly disappointed when the sensor decided to pick up something else. Now, how does this help us (besides knowledge being power)? Is a larger AF sensor more detrimental? When I to center AF, I generally want that little cross (t) to be my guide. Having the big circle could suck, if my target is smaller than the circle, right? What techniques can be used to give us that little bit more edge when dealing with a bigger AF sensor? Or am I talking out of my ass here, since this thread moved so fast from "the center AF point is big" to "OH MY GOD IT ALL MAKES SENSE NOW"....

03-05-2012, 01:30 PM	#43
westmill Veteran Member Join Date: Jan 2012 Location: Stoke on Trent Photos: Gallery \| Albums Posts: 1,146	Originally posted by JinDesu Just jumping in here to ask a question - From what I'm reading here, it is trying to say that the center point AF sensor (and I assume the rest of them) are quite large (as large as the center circle) and hence people who were expecting to focus on an object within that circle were highly disappointed when the sensor decided to pick up something else. Now, how does this help us (besides knowledge being power)? Is a larger AF sensor more detrimental? When I to center AF, I generally want that little cross (t) to be my guide. Having the big circle could suck, if my target is smaller than the circle, right? What techniques can be used to give us that little bit more edge when dealing with a bigger AF sensor? Or am I talking out of my ass here, since this thread moved so fast from "the center AF point is big" to "OH MY GOD IT ALL MAKES SENSE NOW".... Errrrrrr Nope... you got it wrong lol

03-05-2012, 01:32 PM	#44
JinDesu Veteran Member Join Date: Jun 2011 Location: New York City Photos: Gallery Posts: 5,638	Originally posted by westmill Errrrrrr Nope... you got it wrong lol oof! Well I sort of figured, but it was a start to get more explanation! So bigger AF points = better? Or what is it?

03-05-2012, 01:39 PM	#45
westmill Veteran Member Join Date: Jan 2012 Location: Stoke on Trent Photos: Gallery \| Albums Posts: 1,146	Originally posted by JinDesu oof! Well I sort of figured, but it was a start to get more explanation! So bigger AF points = better? Or what is it? It would be easier for you to read the first page that explains it quite well. rather than me or anyone going through it all over again lol. Certainly not better and prob worth reading matey