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09-03-2008, 11:58 PM   #1
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If you can't focus with your Pentax...

Have you tried 'back button focus'?

That is all I use, and I always nail like 90% of my shots....

may the thread continue!

09-04-2008, 12:05 AM   #2
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QuoteOriginally posted by MJB DIGITAL Quote
Have you tried 'back button focus'?

That is all I use, and I always nail like 90% of my shots....

may the thread continue!
I use it always. If the subject will be always at the approximate distance I just fire away and I don't have to wait for focus acquisition. Though sometimes, my k100d doesn't fire right away as I press the shutter button. It just waits a bit and then fires.
09-04-2008, 01:03 AM   #3
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I prefer back AF button. Separated AF and exposure measurement works in much more logical way and AF does not have to engage so often. Choose your focus target, press AF button, recompose, measure light/compensate and fire away! It sounds like it takes much more time than it really does. Maybe fast action/focus tracking situations could benefit from focus/exposure tied together on the same button.
09-04-2008, 01:19 AM   #4
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I have a K100D and I've bound AF to the "OK" button, and use it the same way.

09-04-2008, 01:38 AM   #5
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Cant say I even thought of this.
So you are saying, disable AF on the shutter button? And only use it on the AF or OK button?
If so, when does AE happen?
09-04-2008, 01:41 AM   #6
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QuoteOriginally posted by marlon Quote
Cant say I even thought of this.
So you are saying, disable AF on the shutter button? And only use it on the AF or OK button?
If so, when does AE happen?
I do that on my K100D. You have a dedicated AF button on your K20D, so you don't need to fiddle in the custom menu for that.


In my case AE happens both when you press the shutter button and when you press the OK button to focus.
09-04-2008, 02:00 AM   #7
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For those who are using the rear AF button, make sure you still half press the shutter button. The SR doesn't seem to work fully unless the shutter button is half pressed for about a second before the exposure (you will see the hand icon when it is ready). Does anyone know if there's a way to enable SR with the AF button?

I'm not sure what is going on with the second delay before SR is fully active, but it sounds like SR is partially active if you take a picture before the hand is active, and fully active if you wait for the hand icon. Maybe the shift sensors require time to initialize but the rotation sensor doesn't? Anyone know about this stuff?
09-04-2008, 02:06 AM   #8
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Yes, that would make sense for the SR to calibrate/initialize itself to the current situation, as it has ot get the movement state at that point, and calculate what's needed.

However, 1 second sounds long, I never thought about that, I always just half-press and shoot, and this would explain alot of my motion blurred images. Thanks for mentioning that Walter.

09-04-2008, 02:13 AM   #9
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QuoteOriginally posted by marlon Quote
Cant say I even thought of this.
So you are saying, disable AF on the shutter button? And only use it on the AF or OK button?
If so, when does AE happen?
I like having the the AF on the shutter button disabled so I can focus-recompose in AF.C mode.

I'm not sure, but I think the exposure is continuously updated until just before the picture gets taken. I don't think the AF button changes things other than it activates the metering the same way half pressing the shutter button does.
09-04-2008, 09:12 AM   #10
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QuoteOriginally posted by marlon Quote
Cant say I even thought of this.
So you are saying, disable AF on the shutter button? And only use it on the AF or OK button?
Yes, that's what they are talking about. I actually have it the other way around - it focuses on shutter press *unless* I press OK to temporarily cancel it. I actually take quite a few pictures with my thumb on the OK button, and should really consider reversing this. Especially since I use MF so often; it's not like I'm *that* accustomed to having focus be "automatic".

Anyhow, basic principle is sound - if you're asking the camera to re-focus on every shot, you're asking for trouble. Focus for the first shot of sequence, then let it ride.

QuoteQuote:
If so, when does AE happen?
That isn't affected. Meaning if you're in an auto exposure mode, it happens on shutter press or whenever you hit the AE-L button to lock it earlier. Or, in M mode, it happens on green button press (Ae-L for cameras without green button).
09-04-2008, 01:33 PM   #11
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Original Poster
QuoteOriginally posted by marlon Quote
Cant say I even thought of this.
So you are saying, disable AF on the shutter button? And only use it on the AF or OK button?
If so, when does AE happen?
Yup, that's what I'm saying. That is the first thing I did when I configured my menus in my first DSLR. I hated having my shutter release button activate my AF.

So, while I'm tracking a subject, my thumb is on the dedicated AF button on the back. Usually, I have the shutter release button pressed halfway, so that my SR is activated. Then when it is time to shoot, I just push the shutter release button. There is zero lag time.

It is much better than having a shutter release/AF/SR button all trying to work at once.

8)

Nice machine these guys have built eh?
09-04-2008, 03:18 PM   #12
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QuoteOriginally posted by MJB DIGITAL Quote
So, while I'm tracking a subject, my thumb is on the dedicated AF button on the back. Usually, I have the shutter release button pressed halfway, so that my SR is activated. Then when it is time to shoot, I just push the shutter release button. There is zero lag time.
Cool technique. What happens when you give it to someone to take a picture of you? I'd bet they're totally confused...same people that want the image to show up on the back LCD
09-04-2008, 05:06 PM   #13
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the only catch i'm finding is that i have to stretch more to reach the OK button with the D-BG3 vertical grip.

otherwise, it's how i've been using my cameras for a while...
09-04-2008, 10:56 PM   #14
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Using the AF button and de-coupling from the shutter button was the first thing I did to my K10D (the one that was stolen) when I bought it. It took me a few frustrating months to figure out how to get the OK button to do AF on my *ist DS (stolen also). Once I figured it out - never looked back.

Also the first thing I did on my new K20D is de-couple AF. I will be d*med if I will let the machine decide what to focus on - that is part of my job. Those who are dependent on AF full time should learn how to control the process rather than having the process control them.

Oh - I do not have one of the grips (yup I have do not have a grip - deal with it), if I wanted a 4lb monster to carry around I would have bought a C*non or N*kon. We have discussed the use of the AF/OK button many times here - do a search and you will see why my soapbox is worn out.

The Elitist - formerly known as PDL
09-04-2008, 11:33 PM   #15
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I'm missing something here; what is the disadvantage of leaving AF on half-pressed shutter button? Seems it can do most anything AF button can do, so for me it's more convenient than "fumbling" for the AF button
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