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03-14-2009, 03:00 PM   #1
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AF button on K20

Does the AF button on the back of the K20 work the same way as the Ok button on the K100? Can I use it with a FA lens?

03-14-2009, 05:07 PM   #2
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Moved to DSLR discussion.

Last edited by Damn Brit; 08-27-2009 at 12:24 PM.
03-14-2009, 05:21 PM   #3
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QuoteOriginally posted by stoge Quote
Does the AF button on the back of the K20 work the same way as the Ok button on the K100? Can I use it with a FA lens?
I can't say how it differs (or doesn't) between cams. Yes, you can use it with your FA lens(es) - at least, my FA 50/1.4 and 100-300, and the FF equivalent Sigma DGL 170-500, all autofocus perfectly well when I hit the AF button.
03-14-2009, 05:35 PM   #4
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I would imagine if you have it configured to *cancel* AF, though, it wouldn't do so with an FA lens - or am I wrong about that?

03-14-2009, 11:37 PM   #5
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Yes - and with FA lenes too

QuoteOriginally posted by stoge Quote
Does the AF button on the back of the K20 work the same way as the Ok button on the K100? Can I use it with a FA lens?
The AF button on the back of the K20D (and the K10D) work just like the OK button on the pre-Kx0D cameras. (page 112 in the K20D manual) The AF button was put there to allow you greater control rather than be the slave of the point and shoot crowd.

As a side note:
I attended a National Geographic seminar on how to make your Wild life/Landscape shots Pop. The NG photographer said that de-coupling AF from the shutter button was one of two (2) settings he used by default on his camera (a series of C*non's), the other custome setting was to display the histogram on the LCD by default.

This is the forth time I have heard that NG photographers = by default = de-couple AF from the shutter button.

Edit: I use this method exclusively - even with my FA 50mm f1.4 - no problem. I Even use it with my Tokina 20-70mm macro.

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Last edited by PDL; 03-14-2009 at 11:39 PM. Reason: FA stuff
03-15-2009, 10:40 AM   #6
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I also de-couple AF from the shutter, but recently I realized that I need to half-press the shutter button earlier or shake reduction doesn't activate in time for my shot.

And yes, the AF button can also be set to disable AF.
03-15-2009, 11:46 AM   #7
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QuoteOriginally posted by Marc Sabatella Quote
I would imagine if you have it configured to *cancel* AF, though, it wouldn't do so with an FA lens - or am I wrong about that?
Actually, when set to cancel AF the AF button will do so with any lens, even with a manual lens (for instance if you've got the camera set for "catch in focus: but there's nothing in focus according to the sensor, the cancel AF button will allow you to get the shot anyway (if you think of it quick enough ), while otherwise the camera won't fire as it's waiting for an in focus indication.) I don't have an FA lens here to test it, but I'm confident it would behave the same as a DA lens.
03-15-2009, 02:47 PM   #8
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QuoteOriginally posted by heliphoto Quote
I don't have an FA lens here to test it, but I'm confident it would behave the same as a DA lens.
The reason I wonder is because with no "quick shift" clutch to allow MF while in AF mode, it might be more complicated than that. Obviously, if I had an FA lens, I'd test it myself, but I do think I recall someone having mentioned that it didn't work.

03-15-2009, 04:34 PM   #9
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QuoteOriginally posted by Marc Sabatella Quote
The reason I wonder is because with no "quick shift" clutch to allow MF while in AF mode, it might be more complicated than that. Obviously, if I had an FA lens, I'd test it myself, but I do think I recall someone having mentioned that it didn't work.
Oh, I see what you're saying... You're correct there - the focus drive train will still be engaged, and you shouldn't turn the focusing ring.

I use AF cancel often for such things as focus and recompose focusing, for instance, maybe I've let off the half press shutter, but I know the lens is still focused - I can just compose the shot, and press the AF button to cancel AF and release the shutter, no need to refocus. That's the way I was thinking of using it with an FA lens too.
03-15-2009, 04:45 PM   #10
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Exactly what I was looking for. While using a FA lens, when using the AF button, does it go to manual focus when you press the shutter release? Or does it have to be a DA lens to work properly? thanks ------ Jeff
03-15-2009, 06:04 PM   #11
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Using a M or FA lens - set the front switch to manual

When you feel the need to use the AF circuits with either a FA or M lens and you want to use only manual - use the switch on the front of the K20D to select AF-M. What that switch does is retract the screw that drives the AF function in the lens.

If you have de-coupled the AF function from the shutter button and engaged it to the AF button on the back, by switching to Manual focus on a you have set the AF lens to pure manual mode. Now here is the interesting part, when you press the AF button - you turn on the AF CIRCUIT's and the little green light will indicate when the subject is in focus.

All the front switch does is retract the screw and disable the motor. The AF circuits still work ---- if ----- you have de-coupled. If you have not de-coupled, then AF does not work at all. (I could be wrong here) Yet another reason to de-couple AF from the shutter button.

Never have the front switch set to AF.s or AF.c and twist the focus ring - on a FA (or AF) lens de-coupled or not. By twisting the focus ring you can/will damage the gears/motor of the AF mechanism. In fact my SF-1 manual explicitly said not to manual focus with any AF lens unless you have set the switch to manual focus. My Tokina AF 28-70mm macro that I got with the SF-1 has a thin non rubber/slick metal focus ring that is maybe 4mm wide. That thing is a real PITA to manual focus with.

Personally - I love the way the DA lenses work with quick shift. I press the AF button with my thumb, release it and have my finger on the focus ring to use my MkI eye-ball to get what I want in focus. The camera does not "choose" what I want in focus.

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Last edited by PDL; 03-15-2009 at 06:07 PM. Reason: can't even spell my own tag
08-27-2009, 06:12 AM   #12
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I apologize if this is a silly question. But can someone describe for me the advantage of using the AF button rather than using the shutter/focus function? I see people mention it allows you to focus and recompose---but you can do that with the focus/shutter coupled by using focus lock.
08-27-2009, 03:49 PM   #13
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QuoteOriginally posted by T_MB Quote
I apologize if this is a silly question. But can someone describe for me the advantage of using the AF button rather than using the shutter/focus function? I see people mention it allows you to focus and recompose---but you can do that with the focus/shutter coupled by using focus lock.
Not a silly question - but one that has been discussed at length here.

From my perspective -
De-coupling AF from the shutter button simply allows for more control over your camera, it also puts the photographer into the same situation that we had for all those years before AF was introduced. Meaning - the act focus/compose/set exposure are separate acts - independent of each other. Where with the "default" mode the focus/compose/set exposure is set to where every time you press the shutter button - focus is forced. If you shoot like I do where I spend most of my time composing the shot rather than focusing.

For instance - I have said this before - shooting a Baseball game.
You are on the first base side shooting what you think will be a play at third. So, you warm up the camera (run finger over the shutter button to turn the electronics on) and focus (push the AF button until focus is achieved) on third base - where the "action" will take place. (Assuming you understand Baseball and the given situation). You meter off of the chest of the third baseman and lock the exposure.
The play commences - you fire off three quick shots, but the runner slides beyond third base - after you have your three shots. You have removed your finger from the shutter button. You fire off three more shots as the runner is tagged out.

Now if you had NOT de-coupled - those last three shots would have been most likely missed while the CAMERA decided what to focus on. The third baseman, the runner or someone in the crowd 100 feet behind the bag.

Could you have done this by using the AF button to turn off AF? Yes, but I prefer to tell the camera what to do and when to do it. I do not want the camera to do the thinking for me. If you do not de-couple AF, then the CAMERA is making the decisions - not the photographer.

For me, it basically comes down to who is in control. Now AF will focus faster than I would/could back in the manual days. That is why I use AF most of the time - but the camera focuses on what I tell it to when I tell it to.

Most of the images I miss are because I get lazy and let the camera do the thinking.

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08-27-2009, 03:57 PM   #14
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Ok. That makes sense. I have had that happen for night shots ( I mostly do landscape and architecture), where I am shooting a building or scene. Sometimes when I recompose the camera tries to focus on another object (like an errant passerby), but can't quite get a focus and so I spend 30 seconds watching and listening to the drive motor go back and forth.

You are saying that by using the AF button in conjunction with the shutter decoupled, that I only need to focus once, and then can recompose as many shots as I want of the building without having to worry about the camera trying to refocus.

I suppose that is also useful if you want to focus first and then meter off of something other than what you are focusing on.


Thanks.
08-27-2009, 09:35 PM   #15
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QuoteOriginally posted by PDL Quote
Could you have done this by using the AF button to turn off AF? Yes, but [
What re-starts AF after it has been cancelled? Does it need to be turned off again in between the two series of shots described above?

Another thing to consider is which control dial is primarily being used. AF button doesn't work well for me if I'm using the rear e-dial -- I often end up on the EV-comp button. I run into a far more serious problem if I re-program the front e-dial to be the primary control wheel -- I have a tendency to mistake the power on/off button as the front e-dial sometimes, when moving back from the shutter, thereby shutting the camera down. Then there is the grip, which doesn't have its own AF button.

On the other hand, holding the shutter half-pressed feels like riding the clutch. Sometime it seems to me -- correct me if I'm wrong here -- that if the shutter is held half-pressed too long, it can come out of lock and restart AF, or starts to micro-adjust focus continously (you can hear the motor grinding away). This may be more damaging than anything else.

In any case, and despite the fact that I have not yet done so, my impression is that decoupling AF from the shutter is the way to go. It's just a matter of getting used to it, eventually.
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