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04-28-2013, 12:53 PM   #1
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AF.C (Focus-prority) with the AF button

I like to focus with a dedicated AF button (and half-pressing the shutter release button doesn't make a camera focusing). It works OK.
Today I tried to shoot in the AF.C mode with the Focus-priority submode enabled. To my surprise, I found that the Focus-priority submode had been already enabled. However, it seems that this mode doesn't work with the AF button. I mean, if one is pressing the AF button and the AF isn't locked, there shouldn't be any shots after full-pressing the shutter release button. Nevertheless, it is still possible to make a shot even when the AF isn't locked. Why is that?

04-28-2013, 12:55 PM   #2
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In afc the shutter will release even if the AF isn't locked. That's just how continuous mode works.

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04-28-2013, 01:15 PM   #3
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As Adam said, as the continuous mode never locks it always allows you to shoot. In my experience focus priority means that the camera will make short pauses when shooting longer bursts to leave the mirror down enough time to allow the AF to get focus again before letting the mirror up again for the picture. If shooting in the other mode the camera will always shoot bursts at full speed but as the camera can't focus with the mirror up it can't focus between the shots.

This is one huge advantage to cameras having phase detection AF points on the sensor with a fast enough processor to focus while taking pics, they don't suffer from the AF black out.
04-28-2013, 01:58 PM   #4
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QuoteOriginally posted by Adam Quote
In afc the shutter will release even if the AF isn't locked. That's just how continuous mode works.
Adam, I suppose you're not correct here.
Even in the AF.C mode in the "C3/16. AF.C Setting" menu one can choose between Focus-priority and FPS-priority.

If I turn off autofocusing with the AF button the Focus-priority mode is working OK with the shutter release button (in the AF.C mode).
The question is - why does the Focus-priority works with the shutter release button but doesn't work with the AF button?

P.S. I found the same talk in a Nikon D800 forum. One person was complainig that when he had a Nikon D700, these modes with the AF-on button worked as they should. However, in his newer camera, D800, changing these modes does nothing. He also told that this problem decreased his keepers a lot. So I decided to check these modes in my K-5 IIs...


Last edited by skyer; 04-28-2013 at 02:08 PM.
04-28-2013, 02:19 PM   #5
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This problem drove me nuts on the weekend; Hi burst drive mode, AF-C, focus priority, rear button focus.... yet it would take over a second or 2 to begin it's burst which meant I missed a lot of moments Switching to release priority merely meant the camera made no attempt to focus at all and I'd get 15 OOF shots. I tihnk a bit has to do with the lens mounted, I had the infamous slow focuser 50-135 on at the time. When it gets it right the 50-135 is fantastic, but I've lost faith in it as a sports lens.
04-28-2013, 02:43 PM   #6
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QuoteOriginally posted by twitch Quote
This problem drove me nuts on the weekend; Hi burst drive mode, AF-C, focus priority, rear button focus.... yet it would take over a second or 2 to begin it's burst which meant I missed a lot of moments Switching to release priority merely meant the camera made no attempt to focus at all and I'd get 15 OOF shots. I tihnk a bit has to do with the lens mounted, I had the infamous slow focuser 50-135 on at the time. When it gets it right the 50-135 is fantastic, but I've lost faith in it as a sports lens.
It's strange.
1) Why did it took 2 seconds to begin a burst? During my today tests (AF.C, focus priority, rear button focus, Hi burst) I got a lot of shots rightaway.
2) Why did your camera not try to focus in the AF.C + focus priority? I also tried these modes myself today, my camera focused before each shot.

However, it's a little bit off-topic. Is there still a way to get a focus priority in the AF.C + AF button on?
04-28-2013, 03:35 PM   #7
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What lens are you using?
04-28-2013, 07:00 PM   #8
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QuoteOriginally posted by skyer Quote
Adam, I suppose you're not correct here.
Even in the AF.C mode in the "C3/16. AF.C Setting" menu one can choose between Focus-priority and FPS-priority.

If I turn off autofocusing with the AF button the Focus-priority mode is working OK with the shutter release button (in the AF.C mode).
The question is - why does the Focus-priority works with the shutter release button but doesn't work with the AF button?

P.S. I found the same talk in a Nikon D800 forum. One person was complainig that when he had a Nikon D700, these modes with the AF-on button worked as they should. However, in his newer camera, D800, changing these modes does nothing. He also told that this problem decreased his keepers a lot. So I decided to check these modes in my K-5 IIs...
Read the post I posted above. I notice a difference between the modes but only AF-S can use the "only shoot when locked".
QuoteOriginally posted by twitch Quote
This problem drove me nuts on the weekend; Hi burst drive mode, AF-C, focus priority, rear button focus.... yet it would take over a second or 2 to begin it's burst which meant I missed a lot of moments Switching to release priority merely meant the camera made no attempt to focus at all and I'd get 15 OOF shots. I tihnk a bit has to do with the lens mounted, I had the infamous slow focuser 50-135 on at the time. When it gets it right the 50-135 is fantastic, but I've lost faith in it as a sports lens.
If you're in AF-C it should shoot almost instantaneously. I use it a lot for sports and my brother tried his 50-135 one hockey game and had no problem at all. Maybe SDM issues on the way?

04-28-2013, 10:34 PM   #9
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QuoteOriginally posted by twitch Quote
What lens are you using?
Tamron 17-50/2.8. I also have a 50-135/2.8 lens. When I was shooting last time in the same modes, everything worked as intended too.
QuoteOriginally posted by VisualDarkness Quote
As Adam said, as the continuous mode never locks it always allows you to shoot. In my experience focus priority means that the camera will make short pauses when shooting longer bursts to leave the mirror down enough time to allow the AF to get focus again before letting the mirror up again for the picture.
Frankly speaking, I didn't get your point here.
I'm aware of the fact that in the focus priority mode a frame per second rate will be lower than in the shutter priority or MF. It also means (to my thinking) that if the focus priority mode is enabled and the AF is not locked, there shouldn't be any shots even if one full presses the shutter button.

I made a test.
In the (Hi + AF.C + focus priority + AF button off) mode I pointed my camera at a distant object, full pressed the shutter release button - AF locked, click! click! click! Still pressing the shutter release button (SRB), I then quickly pointed the camera at an object that was closer than a minimal focusing distance of the lens - AF was not locked, the camera didn't shoot. Then, still pressing the SRB, I pointed the camera at another more distant object - AF locked, click! click! click!
In the (Hi + AF.C + focus priority + AF button on + continious pressing the AF button) mode I did exactly the same but the camera continued to shoot even when I pointed the camera at the object that was closer than a minimal focusing distance and AF wasn't locked.
So why is there such a difference in the camera's behaviour because of the rear AF button?

Last edited by skyer; 04-29-2013 at 03:18 AM.
04-29-2013, 01:41 AM   #10
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QuoteOriginally posted by skyer Quote
I made a test.
In the (Hi + AF.C + focus priority + AF button off) mode I pointed my camera at a distant object, full pressed the shutter release button - AF locked, click! click! click! Unpressing the shutter release button (SRB), I then quickly pointed the camera at an object that was closer than a minimal focusing distance of the lens - AF was not locked, the camera didn't shoot. Then, still unpressing the SRB, I pointed the camera at another more distant object - AF locked, click! click! click!
In the (Hi + AF.C + focus priority + AF button on + continious pressing the AF button) mode I did exactly the same but the camera continued to shoot even when I pointed the camera at the object that was closer than a minimal focusing distance and AF wasn't locked.
So why is there such a difference in the camera's behaviour because of the rear AF button?
It looks like this doesn't work as would be expected. That's a bummer and life goes on.
04-29-2013, 03:23 AM   #11
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My works ok.
04-29-2013, 05:37 AM   #12
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QuoteOriginally posted by skyer Quote
Tamron 17-50/2.8. I also have a 50-135/2.8 lens. When I was shooting last time in the same modes, everything worked as intended too.
Frankly speaking, I didn't get your point here.
I'm aware of the fact that in the focus priority mode a frame per second rate will be lower than in the shutter priority or MF. It also means (to my thinking) that if the focus priority mode is enabled and the AF is not locked, there shouldn't be any shots even if one full presses the shutter button.

I made a test.
In the (Hi + AF.C + focus priority + AF button off) mode I pointed my camera at a distant object, full pressed the shutter release button - AF locked, click! click! click! Still pressing the shutter release button (SRB), I then quickly pointed the camera at an object that was closer than a minimal focusing distance of the lens - AF was not locked, the camera didn't shoot. Then, still pressing the SRB, I pointed the camera at another more distant object - AF locked, click! click! click!
In the (Hi + AF.C + focus priority + AF button on + continious pressing the AF button) mode I did exactly the same but the camera continued to shoot even when I pointed the camera at the object that was closer than a minimal focusing distance and AF wasn't locked.
So why is there such a difference in the camera's behaviour because of the rear AF button?
I see your point and as I've only used AF button on for focus for a very limited time that may be why I haven't seen this behavior.
04-29-2013, 05:51 AM   #13
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QuoteOriginally posted by skyer Quote
Tamron 17-50/2.8. I also have a 50-135/2.8 lens. When I was shooting last time in the same modes, everything worked as intended too.
Frankly speaking, I didn't get your point here.
I'm aware of the fact that in the focus priority mode a frame per second rate will be lower than in the shutter priority or MF. It also means (to my thinking) that if the focus priority mode is enabled and the AF is not locked, there shouldn't be any shots even if one full presses the shutter button.

I made a test.
In the (Hi + AF.C + focus priority + AF button off) mode I pointed my camera at a distant object, full pressed the shutter release button - AF locked, click! click! click! Still pressing the shutter release button (SRB), I then quickly pointed the camera at an object that was closer than a minimal focusing distance of the lens - AF was not locked, the camera didn't shoot. Then, still pressing the SRB, I pointed the camera at another more distant object - AF locked, click! click! click!
In the (Hi + AF.C + focus priority + AF button on + continious pressing the AF button) mode I did exactly the same but the camera continued to shoot even when I pointed the camera at the object that was closer than a minimal focusing distance and AF wasn't locked.
So why is there such a difference in the camera's behaviour because of the rear AF button?
This is exactly as I'd expect, you not pushing AF overrides focus priority. They are conflicting messages and pentax decides to trust external control than menu item.

Last edited by twitch; 04-29-2013 at 05:59 AM.
04-29-2013, 05:57 AM   #14
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Try this test, it puzzles me.

With Hi fps, rear AF button enabled and AF disabled from shutter, AF-S mode.

Test 1: push rear AF button to get lock. Release AF button. Now push and hold shutter and listen to FPS.

Test 2: same as above but do not release AF button while pushing shutter. Listen to FPS.

Why oh why is FPS much slower in test 1 than test 2
04-29-2013, 05:59 AM   #15
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QuoteOriginally posted by twitch Quote
This is exactly as I'd expect, you not pushing AF overrides focus priority.
Ah, now I read it again and I think you nailed it Twitch. The P needs to keep holding the AF button down as it came goes into some kind of MF mode when releasing it.
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