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11-12-2009, 01:58 PM   #1
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Manual vs AF

As Ive been taking more and more pics, seems that sometimes, and maybe its me not doing something right, that the AF lens sometimes doesnt do so well sometimes. Seems like its off slightly.

This isnt the majority of time so I would guess its me or limitations of the AF or both?

I also notice that when I use my other MF lens, I get it focused more than not.


So is it better to MF or AF or is it something Im not doing correctly sometimes that gets the AF off

11-12-2009, 02:16 PM   #2
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It could be anything.

Are you using a single focus point? Are you in incandescent lighting (causes front focus on all but K-7)?

You can try out a focus chart:

https://www.pentaxforums.com/forums/pentax-dslr-articles/61385-autofocus-adjustment-hints.html
11-12-2009, 02:31 PM   #3
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Go through your AF technique and scrutinise it before giving up on AF.
Get the theory of AF use and see if your results stack up in more controlled conditions.
11-12-2009, 03:23 PM   #4
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By far the most common cause of AF problems is not doing an adequate job of telling the camera where to focus - either one makes no effort at all, orone tries to select a focus pointnear where one wants, but the actual focus sensor is far too broad to pinpoint that precisely, so the camera uses that focus "point" but focuses somewhere "near" it instead of where you expected. Feel free to post a sample of two, desribing how you tried to tell the camera where to focus (eg, by selecting the focus point, or by using the center point and focus-recompose).

11-12-2009, 03:37 PM   #5
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I dont have a AF "technique" so i will have to research that more.

As for a single focus point, well havent really been keeping detail of what I did to get it to happen and I noticed it both in and outdoors, so i will have to closely monitor what I am doing more as Im taking the pics and havent gotten to using a focus chart yet, but I will now!

and Marc, yes, that seems about right, since looking back, seems I was maybe to broad in my focus points and not giving it much effort since I didnt realize it took that much effort with AF, and with my MF, I gave it much more effort and maybe thats why I got better results.


So what im hearing is that AF does just as well as MF and AF takes as much effort to focus properly as MF and I need to get a focus chart and read over AF theory!
11-12-2009, 04:02 PM   #6
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I wouldn't go that far. You do need to tell the camera which AF point to use if you expect to get the focus to be anywhere even remotely near where you want it - it can't read your mind. In "many" cases, that's good enough - just select the focus point (or use center point and make sure your subject is at center when you focus) and you're good to go. But there are sistuations when that's not quite good enough if your subejct is smaller than the area covered by the AF sensor, or if you you are shooting a very fast lens and DOF is very shallow, so even the slgihtest discrepancy would affect the results. you don't need to mess with focus charts unless you actually suspect a defective camera, but at this point, there is absoluely no reason to be suspecting that - you haven't described anything that sounds even the slightest bit out of the oridnary. If you haven't thought about where the camera is focusing, no surprise it isn't focusing where you wanted.
11-12-2009, 06:44 PM   #7
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gotcha, ill be more aware of that now.
11-13-2009, 05:57 AM   #8
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Here is a classical example of what Marc is talking about. There was no way that I could get camera to focus on the Deer's head eye area with af. I set my camera's at center point, get close with af then switch to mf.


jim

11-13-2009, 06:54 AM   #9
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Pentax uses fairly large AF points, so even if you pick the right one, the sensor may focus on the wrong thing (the shot of the deer could be a poster boy for this).
Also, I honestly don't find Pentax's AF to be especially accurate. It's fine when the lens is stopped down because depth of field maskes the error, but shooting close to wide open with my DA*55/1.4 tends to show up focus inaccuracy.
It's quite annoying, but it's what we are given to work with.
11-13-2009, 06:58 AM   #10
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I have seen a few different user initiated AF errors.

With long lenses, the camera shake causes the AF lock to be on other than what you think you focused on.

with any lens, and stationary objects, some times I have seen AF-C snap in on focus then re-adjust out of focus. I suspect that AF C is much more appropriate for moving subjects and AF-S is for stationary. The issue is that in AF-S moce the shutter is interlocked with focus confirmation, so mopst people use AF-C so the shutter can trigger without AF confirmation.

I wish there was an override for this,
11-13-2009, 07:13 AM   #11
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If there are any contrasting lines near the focus point, forget AF, even with center focus.
This is why a have a split screen in the K200D.

Last edited by wildlifephotog; 09-27-2013 at 07:25 AM.
11-13-2009, 10:28 AM   #12
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QuoteOriginally posted by Lowell Goudge Quote
with any lens, and stationary objects, some times I have seen AF-C snap in on focus then re-adjust out of focus. I suspect that AF C is much more appropriate for moving subjects and AF-S is for stationary. The issue is that in AF-S moce the shutter is interlocked with focus confirmation, so mopst people use AF-C so the shutter can trigger without AF confirmation.

I wish there was an override for this,
I don't use AF-C, but I have my OK button set to to cancel AF (other cameras have a AF button that can be used in this way). I use this to temporarily disassociate AF from shutter half-press, but I wonder if this wouldn't perhaps also work in AF-C mode to do what you are suggesting?
11-13-2009, 10:47 PM   #13
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QuoteOriginally posted by Marc Sabatella Quote
I don't use AF-C, but I have my OK button set to to cancel AF (other cameras have a AF button that can be used in this way). I use this to temporarily disassociate AF from shutter half-press, but I wonder if this wouldn't perhaps also work in AF-C mode to do what you are suggesting?
That's a great idea. Thanks.

michael mckee
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