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01-28-2009, 09:16 PM   #1
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tips on AF-ON usage

I know, not from a pentax source but still useful if you want to know how best to use it...

Understanding the Nikon Multi-CAM2000 Autofocus System

01-29-2009, 12:11 AM   #2
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Old Feature..

QuoteOriginally posted by kenyee Quote
I know, not from a pentax source but still useful if you want to know how best to use it...

Understanding the Nikon Multi-CAM2000 Autofocus System
We Pentaxians had that dedicated AF button back to the MZ-S days and of course if we do not press the AF button anymore, the AF will be locked "automatically". And of course x 2 that this AF button has nothing to do with the shutter release and so AF can be worked independently.

Brilliant early (original?) Pentax design?
01-29-2009, 12:51 AM   #3
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QuoteOriginally posted by kenyee Quote
I know, not from a pentax source but still useful if you want to know how best to use it...
Understanding the Nikon Multi-CAM2000 Autofocus System
You mean this passage?
QuoteQuote:
Let's face it, lots of things don't stand still long enough to lock focus and then recompose. But what about those times when you are tracking a moving subject and then it stops long enough for you to actually compose a nice shot? If you are in AF-C mode and you have the AF activation linked to the shutter, if you recompose the shot the AF system will engage and reacquire focus on whatever is in the bracket. Not good. You'd have to switch to AF-S mode, and then hope your subject doesn't start moving again. Well, if you set custom setting a5 to OFF (AF-ON only), and you have AF-C set to release priority (fps rate), then you can get the best of both worlds!

1) Follow your subject continuously by pressing the AF-ON button.

2) When your subject stops, focus on the point of interest and then RELEASE the AF-ON button.

3) Recompose and shoot.
Yes, good tip!
01-29-2009, 08:46 AM   #4
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Yep, that's the tip. I think the only thing I'd wish for is the choice of focus priority instead of release priority for AF-C.
I've been trying to get used to AF-ON again because some DPR Nikon D300 users still use it because Nikon's best AF system doesn't always read your mind ;-)

01-29-2009, 11:49 AM   #5
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Another good thread w/ AF-ON tips:
Problem with continuous focus... - NikonCafe.com
01-29-2009, 07:28 PM   #6
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ok...dumb question time:
Why would you ever use AF-S mode if you use AF-ON and focus w/ the AF button? It seems to let you blast away w/ nothing in focus, just like AF-C mode...
01-29-2009, 10:59 PM   #7
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QuoteOriginally posted by kenyee Quote
ok...dumb question time:
Why would you ever use AF-S mode if you use AF-ON and focus w/ the AF button? It seems to let you blast away w/ nothing in focus, just like AF-C mode...
No such thing as a dumb question.

One uses the [AF] button on the back of one's Pentax instead of the half press (you can turn it off in the custom settings) to avoid the time loss while the camera refocuses where you have it focused already, or instead of doing the half press + hold + recompose style of holding the AF, you press the AF button, again with half press auto focus disabled, and the camera only focuses when you press the AF button.

Also if you are using the button you can program it to cancel AF for a shot or two - helpful when AF-C goes wild, although I have never used it myself.
01-30-2009, 12:19 AM   #8
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For the K10D I can't think of any reason to have both buttons programmed as AF-ON. I therefore have the AF button set to AF-OFF.

On the K20D there is one usefulness to have the AF button on ON. When you are in Lifeview and press the AF button, it closes Lifeview for a moment and does an AF. This does not work with the shutter button.

01-30-2009, 07:54 AM   #9
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Thanks for the replies (and the interesting liveview feature I didn't know about :-)

My question was actually a bit more specific to AF-S vs AF-C mode.
If I have AF-ON enabled, if affects both AF-S and AF-C mode (I think...but blende8 seems to imply it's separate for both?)
So if I turn on AF-ON, why would I even use AF-S any more? Why not just leave the camera in AF-C? That's why I was surprised AF-S + AF-ON didn't act more like focus trap (use AF-S to set the focus at some distance, then press the shutter so it fires when something is in focus at that distance).
01-30-2009, 12:39 PM   #10
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FYI, I asked a Nikon D80 friend and this is what AF-ON does in AF-S mode on it:
---------
With AF-S, and activating the AF-ON feature, half-pressing the shutter
does nothing (the "decoupling" of focus control from the shutter
release that so may guys prefer). Pressing AF-ON and NOT releasing it
engages a continuous auto-focus. So long as I have my finger on it,
the camera keeps continuously focusing as I move around. Only when I
release the AF-ON button does it stop focusing. After releasing the
AF-ON button, if I press the shutter release while the focus point is
NOT in focus, the shutter does NOT fire. This is the "Nikon version"
of "focus trap." (I think they use another term for it -- if anything,
it is focus-priority). If I press the shutter while the focus point
is in focus (green dot), it will fire immediately. If I press and
HOLD the shutter button while the focus point is OUT of focus, it will
not fire, but as soon as I pan to a point where the focus point is in
focus, it will fire automatically, without me pressing anything.
Hence, an AF version of focus trap. Another key point -- after the
shutter is released, the AF is still "locked" into that same position
as before, so I can take another shot with focus trap.
---------

Unfortunately, on the K10D/K20D, AF-ON w/ AF-S seems to act exactly like AF-ON w/ AF-C which also matches what the D80 does in AF-C:
---------
With AF-C, and activating the AF-ON "feature", half-pressing the
shutter does nothing. When I press the AF-ON button, the camera will
continually autofocus so long as I keep the AF-ON button pressed.
Only when I let it go does it stop focusing. When I press the shutter
fully, it fires regardless of whether the focus point is in focus or
not. After the shot, focus is still locked in the previous position
and another full press fires the shutter again.
--------


Seems like Pentax should have set up the AF-ON in AF-S to work like Nikon did so it's more useful :-P
01-30-2009, 09:30 PM   #11
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The use of the AF button to de-couple AF from the shutter button has been beaten to near death here, so again, here is my put.

Once I learned how to de-couple AF from the shutter button on my *ist Ds - I never looked back. This was the first thing I did on both the K10D and K20D that I have now. Default setups are for newbies (it works and works well, but I prefer to have control over what happens - the camera will not "decide" what is in focus, I will).

When using the AF button and AF-S - the system will find focus and stop. Just like the manual days. I also only use the center AF point.

When using the AF button and AF-C (something I rarely do) as long as you keep the AF button pushed it will track. When you release the button - it will stop ------ DUH!

As for whether the shutter button will actually take an image - in AF-S the shutter button acts - like a shutter button - push it and it takes an image. Just as it is supposed to - again the photographer is in control.
With AF-C - I can not comment, since I do not use it - I have tried a few times, but again I want to be in control, not the camera.

As for N*kon's method --- I don't care - I do not have a N*kon, I have a Pentax.

The Elitist - formerly known as PDL
01-31-2009, 09:55 AM   #12
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QuoteOriginally posted by PDL Quote
T
When using the AF button and AF-S - the system will find focus and stop. Just like the manual days. I also only use the center AF point.
When using the AF button and AF-C (something I rarely do) as long as you keep the AF button pushed it will track. When you release the button - it will stop ------ DUH!
Thanks PDL. I didn't notice AF-S only uses the center AF point.
But your usage only seems to emphasize what I found...you could just leave yours on AF-C when using the AF button and not ever need to use AF-S, so that mode seems redundant. Thanks for confirming.

Also, if you turn on AF button usage, it stays on in AF-S and AF-C mode...you can't turn it on only for AF-C mode.

Back to practicing AF-ON usage and leaving it set to AF-C now that I've confirmed there's no real reason to leave it in AF-S mode...
02-01-2009, 11:28 PM   #13
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Not Quite

QuoteOriginally posted by kenyee Quote
Thanks PDL. I didn't notice AF-S only uses the center AF point.
But your usage only seems to emphasize what I found...you could just leave yours on AF-C when using the AF button and not ever need to use AF-S, so that mode seems redundant. Thanks for confirming.

Also, if you turn on AF button usage, it stays on in AF-S and AF-C mode...you can't turn it on only for AF-C mode.

Back to practicing AF-ON usage and leaving it set to AF-C now that I've confirmed there's no real reason to leave it in AF-S mode...
Just to verify -
AF de-coupled from shutter button.

Selected AF-S and switched to use all focus points (K20D switch pointed to Auto on back of camera) Point camera at an object - camera uses ALL focus points and stops when the CAMERA decides what object is in focus. Point camera in another direction - no focus until YOU push the button and ALL focus points are used. In my mind bad scenario - I want to decide what is in focus - the selection is one switch away. I use, and prefer, to use the center focus point - due to age and habit, also I decide what object is to be in focus - not the CAMERA (bad bad bad)

Selected AF-C and switched to use all focus points (K20D switch pointed to Auto on back of camera) Point camera at an object - camera uses ALL focus points and stops when YOU release the AF button. Point camera in another direction - no focus until YOU push the button and ALL focus points are used. When holding down the AF button - focus changes as camera is moved. Again in my mind bad scenario - I want to decide what is in focus.

If you set the camera to AF-M, it retracts the screw drive and effectively removes functional AF from the lens/camera. However, if you have AF de-coupled from the shutter button, you can press the AF button and manuall focus the lens, the AF circuits will be turned on and the hexagon "Focus Assist" will activate and light up when the CAMERA determines that the subject is in focus - depending on what focus spot YOU have selected.

Also note - if you are using an A lens and manually focus - turning the focus ring and thereby mechanically turning the AF motor - you can DAMAGE the camera - do not do this. Turn the front switch to manual and use manual focus.

The really nice thing about Pentax Lenses is that with the quick-shift focus - you have the ability to use the Mark-I eye-ball without swiching anything. Unless you are using AF-C and half shutter button - where the camera thinks it is in charge. Needless to say; My cameras are never "in charge" -- I am.

The Elitist - formerly known as PDL

Last edited by PDL; 02-01-2009 at 11:34 PM. Reason: editing and ephasis
02-02-2009, 08:56 AM   #14
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thanks PDL. I did notice that I could select the focus point in AF-S and AF-C with AF-ON; if you use a single AF point, I still wouldn't use AF-S. I'd just use AF-C all the time and rotate the AF dial from single to Auto if there's only one thing moving in the scene.

Tried it out this weekend and found I kept making mistakes like forgetting to use the AF button and forgetting to hold the shutter down for .5sec to kick in SR. I also wish the exp comp and AF buttons were swapped...guess my thumb is a bit too long
Need more practice...

Also found that 1/180s is *not* fast enough to freeze motion for lion dances
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