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AF-C mode?

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brandrx

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In AF-C mode the shutter will fire even if the subject is out of focus. Since those out of focus shots are unusable then why allow them in the first place?

What I would like to see is the shutter unable to fire unless the subject is in focus when in AF-C mode, even if it means less FPS. It would be like Catch-in-focus (focus trapping) only with autofocusing instead of your fingers turning the focusing ring.

Is there something I don't understand here? Please enlighten me.

Cheers.

--
Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'

'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

Ron ~ Retired.
 
Hi Ron

I find AF-C mode useless. I hardly ever use it, and when I do I curse it. Better to risk being a bit off with manual focussing IMHO.

Cheers,

Rod

--
All I want is a digital back for my trusty K1000 . . .
 
brandrx said:
In AF-C mode the shutter will fire even if the subject is out of focus. Since those out of focus shots are unusable then why allow them in the first place?

What I would like to see is the shutter unable to fire unless the subject is in focus when in AF-C mode, even if it means less FPS. It would be like Catch-in-focus (focus trapping) only with autofocusing instead of your fingers turning the focusing ring.

Is there something I don't understand here? Please enlighten me.
Click to expand...
Most cameras have a balance with AF-C: an in focus shot or just shoot at max frame rate regardless of focus. On some pro level cameras this balance can be tweaked through camera settings.

I believe Pentax with the K-2000 and K-7 tweaked this setting to give more priority to focus than taking the shot. I tried with my son with the K2000 riding towards me on his bike and was getting 4/5 shots in focus. With the K-7 I tried with a car and got 8/9 in focus, but the first shot that was out of focus was focused on the wrong truck. I used auto focus point selection, all focus points, and it grabbed the wrong subject initially. In continuous shooting (HI) it took the first shot (out of focus one) then it didn't take another shot for a split second as it changed focus to the truck I wanted, then fired the last 8 shots at 3 fps or higher (didn't look at time stamps to see for sure).

What I notice with both the K-7 and the K-2000 is that the frame rate drops slightly depending on if the camera can maintain focus or not. This to me indicates it is giving some extra priority to getting the focus right before taking the shot. I don't have an older camera to compare it too so I can't see if they changed anything.

Eric

--
I never saw an ugly thing in my life: for let the form of an object
be what it may - light, shade, and perspective will always make it
beautiful. - John Constable (quote)

See my Blog at: http://viking79.blogspot.com/
Flickr Photostream: http://www.flickr.com/photos/28177041@N03/ (updated daily)
See my PPG Shots: http://www.pentaxphotogallery.com/erictastad (6/5/09)
 
brandrx said:
In AF-C mode the shutter will fire even if the subject is out of focus. Since those out of focus shots are unusable then why allow them in the first place?

--
Ron -
Click to expand...
Only manual focus and firing non-stop can cure the problem provided there is a way you can finetune the focus with moving subject.

I have tons of example of using the max number of frames/second (3 for k20d) ONLY with MF and manual metering. An auto function will slow the camera down

Catch-in focus won't work for faster subject particularly in dim light

Daniel, Toronto
http://www.pbase.com/danieltong
 
brandrx said:
In AF-C mode the shutter will fire even if the subject is out of focus. Since those out of focus shots are unusable then why allow them in the first place?
Click to expand...
Because a shot slightly OOF is better than no shot at all.
brandrx said:
What I would like to see is the shutter unable to fire unless the subject is in focus when in AF-C mode, even if it means less FPS. It would be like Catch-in-focus (focus trapping) only with autofocusing instead of your fingers turning the focusing ring.
Click to expand...
As Viking79 said, there is a balance between the two. Unfortunately this balance cannot be tweaked at all on the Pentax cameras, we're left with their engineers choice. AF speed, particularly on the K-7, is not bad at all but sometimes I feel we miss some options to make the most of it.

--
Manu



http://flickr.com/photos/ensh/
Réflex Pentax: http://www.flickr.com/groups/pentaxfr/

My PPG: http://www.pentaxphotogallery.com/home#section=ARTIST&subSection=1312871&subSubSection=3929608
 
viking79 said:
brandrx said:
In AF-C mode the shutter will fire even if the subject is out of focus. Since those out of focus shots are unusable then why allow them in the first place?

What I would like to see is the shutter unable to fire unless the subject is in focus when in AF-C mode, even if it means less FPS. It would be like Catch-in-focus (focus trapping) only with autofocusing instead of your fingers turning the focusing ring.

Is there something I don't understand here? Please enlighten me.
Click to expand...
Most cameras have a balance with AF-C: an in focus shot or just shoot at max frame rate regardless of focus. On some pro level cameras this balance can be tweaked through camera settings.

I believe Pentax with the K-2000 and K-7 tweaked this setting to give more priority to focus than taking the shot. I tried with my son with the K2000 riding towards me on his bike and was getting 4/5 shots in focus. With the K-7 I tried with a car and got 8/9 in focus, but the first shot that was out of focus was focused on the wrong truck. I used auto focus point selection, all focus points, and it grabbed the wrong subject initially. In continuous shooting (HI) it took the first shot (out of focus one) then it didn't take another shot for a split second as it changed focus to the truck I wanted, then fired the last 8 shots at 3 fps or higher (didn't look at time stamps to see for sure).

What I notice with both the K-7 and the K-2000 is that the frame rate drops slightly depending on if the camera can maintain focus or not. This to me indicates it is giving some extra priority to getting the focus right before taking the shot. I don't have an older camera to compare it too so I can't see if they changed anything.
Click to expand...
Hi Eric,

My question is: Why not give 100% priority to in focus?

If I have a manul focus lens and using Catch-in-focus, I can press the shutter and hold it pressed. The shutter will not fire unless the subject is in focus. If I keep the shutter pressed fully, as I am following a moving subject, and focusing the ring, again the shutter will not fire unless the subject is in focus. If I were able to track that moving subject while focusing the ring and while holding the shutter pressed fully, and if I were able to do it all fast enough and smooth enough then every shot would be in focus every time and I could do it in the machine gun mode. So, why can't they do the same thing with AF-C and autofocusing?

Cheers.

--
Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'

'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

Ron ~ Retired.
 
brandrx said:
In AF-C mode the shutter will fire even if the subject is out of focus. Since those out of focus shots are unusable then why allow them in the first place?
Click to expand...
I used AF-C as a sort of workaround whenever my K10D would not lock focus due to low contrast in dim lighting. I know the subject would be in focus because the DOF is deep enough at the selected aperture and I see in the viewfinder that the focus is good enough. But the camera won't fire and I'm losing shots because of it. I would quickly flip the AF switch from AF-S to AF-C and that solves the problem. It may not be what it was intended for, but it was too easy to fix that way.
 
Chris Brace said:
The way i use it is to allow me to half press to focus on a moving target and then choose my time to take the picture, if you press fully first time the image will be out of focus but AFC allows prefocus on a moving target, unlike AFS.
Click to expand...
I understand how AF-C works, I just don't understand why it will allow an out of focus image to be taken. If you do the half-press and then take your first shot, it will probably be in focus, however, if you keep the shutter pressed then any subsequent shots may or may not be in focus because the sutter will fire even if the subject is OOF. Which makes no sense to me. Why allow it to fire if it is OOF?

--
Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'

'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

Ron ~ Retired.
 
D TONG said:
brandrx said:
My question is: Why not give 100% priority to in focus?

Ron ~ Retired.
Click to expand...
I think Corolla has a max speed of 120 MPH. Your question is like asking Corolla to actually give you 120 mph on the road. That is not going to happen
Click to expand...
I think that is a ridiculous analogy. Sorry.

--
Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'

'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

Ron ~ Retired.
 
brandrx said:
What I would like to see is the shutter unable to fire unless the subject is in focus when in AF-C mode, even if it means less FPS. It would be like Catch-in-focus (focus trapping) only with autofocusing instead of your fingers turning the focusing ring.
Click to expand...
Cameras with good autofocus systems have the option to set AF-C to either focus friority or shutter priority.

Anyway, solution for you is very simple:
1) set drive mode to continuous
2) set AF to AF-S
3) press the shutter button.

I'll get exactly what you want.

--
Edvinas
 
brandrx said:
brandrx said:
I think Corolla has a max speed of 120 MPH. Your question is like asking Corolla to actually give you 120 mph on the road. That is not going to happen
Click to expand...
I think that is a ridiculous analogy. Sorry.

--

Ron ~ Retired.
Click to expand...
For K20D , you can only achieve 3fps (AF-C & auto metering) if you do a fixed subject with consistent light. In real life particularly with fast subject, no.

In the case of Corolla which has a 120 mph limit on the speedometer, the speed can be achieved with no road friction and no adverse wind. In real life driving, there is zero way you can do 120 mph with a Corrolla. So you see 3fps and 120mph are theoretical best under controlled environment.

Try look at the exif of your best AF-C ( &Av or Tv) images. You can easily see how many fps you can do. I bet that you cannot find any doing 3pf (with moving subject and changing lighting condiiton) ?????

This challenge is offered to any forum members

Daniel, Toronto
http://www.pbase.com/danieltong
 
brandrx said:
Chris Brace said:
The way i use it is to allow me to half press to focus on a moving target and then choose my time to take the picture, if you press fully first time the image will be out of focus but AFC allows prefocus on a moving target, unlike AFS.
Click to expand...
I understand how AF-C works, I just don't understand why it will allow an out of focus image to be taken. If you do the half-press and then take your first shot, it will probably be in focus, however, if you keep the shutter pressed then any subsequent shots may or may not be in focus because the sutter will fire even if the subject is OOF. Which makes no sense to me. Why allow it to fire if it is OOF?
Click to expand...
The problem is that if you only rely on measuring and confirming the focus on moving subjects then you will probably get only a few shots (or shots that OOF because the subject moved slightly in the delay to get the shot). See it like this

if you gone throw a ball to someone and he is in motion, you are predicting he is at some point when the ball arrives there. You don't know if this gonne happen but expecting this. If the catcher falls then no luck, but most of the times he doesn't fall :)

So more sport cams are doing just this, predicting the subjects place in time and shooting at that focus distance and hope for the best. And most of the time you get excellent results. And that's why we need the FPS flowing for one reason. Only pentax is not very good a predicting hence the slow down.

Another reason is that slightly OOF has good value. When i shoot sports, the clients are mostly trilled with a full sequence, like the run and jump with athletics. And sometimes things are happening not foreseen, like a collision or a fall : then capturing that moment is more important then absolute focus.

Just my view on things based on AF-c experience.

--
Bye4now



http://www.indots.nl

I have the deepest respect for all those people who like me.
 
Edvinas said:
brandrx said:
What I would like to see is the shutter unable to fire unless the subject is in focus when in AF-C mode, even if it means less FPS. It would be like Catch-in-focus (focus trapping) only with autofocusing instead of your fingers turning the focusing ring.
Click to expand...
Cameras with good autofocus systems have the option to set AF-C to either focus friority or shutter priority.

Anyway, solution for you is very simple:
1) set drive mode to continuous
2) set AF to AF-S
3) press the shutter button.

I'll get exactly what you want.
Click to expand...
Sorry but it won't.

The first image will not be taken until the subject is in focus. If the shutter is held pressed fully, then any susequent images will be taken even if the image is not in focus when using AF-S.

--
Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'

'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

Ron ~ Retired.
 
Richard Smals said:
brandrx said:
Chris Brace said:
The way i use it is to allow me to half press to focus on a moving target and then choose my time to take the picture, if you press fully first time the image will be out of focus but AFC allows prefocus on a moving target, unlike AFS.
Click to expand...
I understand how AF-C works, I just don't understand why it will allow an out of focus image to be taken. If you do the half-press and then take your first shot, it will probably be in focus, however, if you keep the shutter pressed then any subsequent shots may or may not be in focus because the sutter will fire even if the subject is OOF. Which makes no sense to me. Why allow it to fire if it is OOF?
Click to expand...
The problem is that if you only rely on measuring and confirming the focus on moving subjects then you will probably get only a few shots (or shots that OOF because the subject moved slightly in the delay to get the shot). See it like this

if you gone throw a ball to someone and he is in motion, you are predicting he is at some point when the ball arrives there. You don't know if this gonne happen but expecting this. If the catcher falls then no luck, but most of the times he doesn't fall :)

So more sport cams are doing just this, predicting the subjects place in time and shooting at that focus distance and hope for the best. And most of the time you get excellent results. And that's why we need the FPS flowing for one reason. Only pentax is not very good a predicting hence the slow down.

Another reason is that slightly OOF has good value. When i shoot sports, the clients are mostly trilled with a full sequence, like the run and jump with athletics. And sometimes things are happening not foreseen, like a collision or a fall : then capturing that moment is more important then absolute focus.

Just my view on things based on AF-c experience.
Click to expand...
You're telling me how AF-C works and I am telling you how I would like to see AF-C work.

Perhaps we need to AF-C modes. (AF-C1) the way it is now and (AF-C2) the way I would like to see it.

--
Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'

'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

Ron ~ Retired.
 
D TONG said:
brandrx said:
I understand how AF-C works, I just don't understand why it will allow an out of focus image to be taken.
Click to expand...
D TONG said:
Ron ~ Retired.
Click to expand...
The camera actually decides that the subject is not OOF in this case. Actually it is backfocusing.

Basically the camera is too slow to react.
Click to expand...
The camera reacts extremely fast if doing Catch-in-focus. So if I were able to move that focus ring fast enough and smothly enough using Catch-in-focus, I could probably get 5 FPS easily and they would all be in focus.
D TONG said:
AF-C definitely works IF the subject is not moving . And all will be in focus
Click to expand...
Why would I even want to use AF-C in this case? Makes no sense.

--
Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'

'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

Ron ~ Retired.
 
D TONG said:
brandrx said:
I understand how AF-C works, I just don't understand why it will allow an out of focus image to be taken.
Click to expand...
D TONG said:
Ron ~ Retired.
Click to expand...
The camera actually decides that the subject is not OOF in this case. Actually it is backfocusing.

Basically the camera is too slow to react.

AF-C definitely works IF the subject is not moving . And all will be in focus
Click to expand...
AF-C works better than you give it credit. The few trials I have done with my K2000 have been about 80% in focus for a subject moving straight at the camera, and the one test with the K-7 was about 90% in focus with a subject moving straight at the camera. Some of those shots could have been a bit sharper, but definitely in the range of acceptable.

Eric

--
I never saw an ugly thing in my life: for let the form of an object
be what it may - light, shade, and perspective will always make it
beautiful. - John Constable (quote)

See my Blog at: http://viking79.blogspot.com/
Flickr Photostream: http://www.flickr.com/photos/28177041@N03/ (updated daily)
See my PPG Shots: http://www.pentaxphotogallery.com/erictastad (6/5/09)
 
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