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03-18-2007, 08:10 AM   #1
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Auto-focus: how do you use it?

Ok, I have never got along with my pentax auto-focus... either from my ZX-5n or now my K100D. It seems to work ok when I play with it or practice, but in real life situations, when I am concentrating on the subject matter, I find the subjects out of focus and the back wall in focus.

Its not the speed, its the decision making...

The problem I am having is that my subject matter is getting faster. My sons basketball games are difficult to track with pre-focus as the action doesnt come in expected spots.

The auto-select focus spot guesses wrong too often, and center spot/recompose doesnt work for me for action shots I am not fast enough recomposing.

So how do you parents use the AF? How do wedding photogs use it? Do I just need MUCH more practice selecting my AF point? What if I hand the camera to my spouse? How do you get the camera to behave decently like a point and shoot?

heres some examples of a once in a lifetime event for my son. I got a few keepers, but the missed shots are haunting me... I felt like I was fighting the autofocus while I was trying to take in the event and frame shots... anything in focus needed cropping as the framing was terrible. anything composed, was focussed somewhere else.

heres a link to the keepers, I attached some trouble makers below...Picasa Web Albums - Carl - 2007_03_17 Et...

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03-18-2007, 08:53 AM   #2
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i usually just leave it on center spot, and focus on the subject. AF-S on the AF mode selector.

AF-C sometimes can get a little too aggressive. from your shots, seems like you were focusing on the wall. where you in selective focus?
03-18-2007, 09:04 AM   #3
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Where's the sin in cropping?

If you simply must focus and recompose, try setting the "OK" button to "Disable AF". Then focus, stab "OK" and reframe your shot before your subject moves too much on you.
03-18-2007, 09:10 AM   #4
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When I first got my K10D I lost a few shots because the background behind the subject was either sky or smooth color, and the AF wasn't totally on the subject - leading to hunting and missed shots. I know you said you did some testing of AF, but if you haven't yet it's worth the time to pick something like the top of a distant flagpole and testing the center AF point to make sure it's actually where you think it is.

I consciously shoot in two primary modes;

1. Thoughtfully: In M mode, MF / ME on old lenses, sometimes AF/AE, but usually with center metering and AF only. I hold, recompose, and release the shutter, but just as you mentioned, this isn't always practical.

2. Wildlife / Action: In P mode, either MTF in outdoors, or High Speed. Sometimes with AF-C, but usually just center AF. If the light is really good I'll switch to Av and try for the greatest DOF so focus is less of an issue; however this can lead to very 'point and shoot' looking shots where the subject isn't isolated at all from the surroundings.

Also, if the subject is solid colored with no texture or pattern for the AF to 'grab', then switch to MF. I read an article on how AF operates, by trying to create the maximum contrast between a small line of AF sensor elements, and you can see that smooth colors are the bane of AF. In some of your missed shots I think the AF was grabbing onto either the lady in the striped top, or as you say, the back wall.

The last thing that I've seen done, but use much myself, is setting up the shot as in #1 - with MF, so you can set the DOF you want at the ISO you need, and at a shutter speed that will still freeze the action - and then waiting for the subject to move itself into focus. With the near zero shutter lag of a dSLR you should be able to snag some shots.

As for shooting with all AF points - my experience is like yours - it's a crapshoot. If there is some magic I'd like to hear it too!

-

N

03-18-2007, 09:22 AM   #5
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QuoteOriginally posted by -=JoN=- Quote
i usually just leave it on center spot, and focus on the subject. AF-S on the AF mode selector.

AF-C sometimes can get a little too aggressive. from your shots, seems like you were focusing on the wall. where you in selective focus?
Hmmm, I was about to say no.. that I was using Auto.... but I decided to check before answering... the camera WAS in selective AF. I guess I had been trying out selective and didnt reset to AUTO or center only...

I thought it was in AUTO while I was shooting... I guess thats why I'm asking how people here use AF. I would like to find a method that works for me so I can get comfortable with it, and stop fiddling with the settings all the time.
03-18-2007, 09:50 AM   #6
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QuoteOriginally posted by kmccanta Quote
Hmmm, I was about to say no.. that I was using Auto.... but I decided to check before answering... the camera WAS in selective AF. I guess I had been trying out selective and didnt reset to AUTO or center only...

I thought it was in AUTO while I was shooting... I guess thats why I'm asking how people here use AF. I would like to find a method that works for me so I can get comfortable with it, and stop fiddling with the settings all the time.
i'd try out just leaving it in center only and see how that works. the auto might go out of center and focus in on something else.

aim at the face too if possible.

you have digital, keep shooting, you'll get it down soon. next thing you know your producing awesome shots.

imagine shooting a roll w/ those results. thats even more frustrating.

try out MF too when the action gets a little slow.
03-18-2007, 10:25 AM   #7
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Kmccanta, I'm a parent, and I've gone through much of the same ordeal. So far, here's what I do to chase my 4 month old:

1) Decouple the shutter from the autofocus. If the k100d allows this, then disable "AF when press halfway" and enable "AF button function" (custom menu). Use your right thumb to autofocus with the AF button and fire the shutter with your right index finger. Few things angered me more than waiting for the AF to quit hunting while I held down the shutter button, only to watch the moment slip away.

2) Often, but not always, I set the AF dial to "select" and move the red dot to where I think my daughter will be. This eliminates the "focus and recompose" step.

3) I always aim for the leading eye of the subject, using the red dot as my "sight". I NEVER use the "auto" (green) position on the AF dial. When shooting guns, as well as photographs, the axiom "aim small, miss small" will serve you well.

Please let us know if this helps.

Here's a pseudo action shot: k10d, 43mm f1.9 ltd: f2.5, 1/15 sec, ISO 400

03-18-2007, 11:15 AM   #8
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Yeah, I went and spent 20 bucks on a used AF zoom lens because I also have a 4-month-old who doesn't like to sit there patiently while Dad sorts through his various MF primes, chooses and mounts one, carefully focuses, and gingerly hits the shutter release. Even worse when it's an M42 and I have to fiddle with an adapter...

And I have absolutely been there, where there's a blurry baby smiling in front of a beautifully rendered houseplant. Ugh.

My solution is always just to take as many shots as I can given the limits of memory buffering and a baby's patience. After reading this thread, though, I think I'll try tinkering with the AF settings a little more.

03-18-2007, 11:22 AM   #9
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I am quite new to my SLR and am always learning. I set my K100D to AF-C to capture some shots of my [grown-up] kids being pulled behind a snowmachine on a toboggan. I was thrilled and amazed at the clarity of the shots. The focus "followed' them nicely and almost all shots turned out great. I can't remember tho if I had it on P or Av.

This is my first time posting pics, hope it works.



03-18-2007, 05:54 PM   #10
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Getting actions shots takes a bit of practice and a lot of patience. It looks like you were using selective focus, as others have said. In my menu, I have the option "Swtch dst msr pt" set to the second option. With the autofocus lenses, I try to use centre as much as possible by pressing ok before shooting.

What I sometimes do with the kit lens is switch to MF. I try shooting in burst while fine tuning your focus between the shots. It's taking a bit of practice. This was one of my attempts taken a while back using the FA 80-200.
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03-18-2007, 06:39 PM   #11
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This is a great teaching thread for the intricacies of AF

I have been using MF for a long time now, mainly due to the mis-focussing of the AF.

I may have to reinvestigate the AF settings for the istDS and see if I can make something out of AF rather than cowering away to MF
03-18-2007, 09:27 PM   #12
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To Mike Cash:
No sin in cropping, I did crop that first one. As long as its not blown up its viewable. Its just taht some shots like the second one, cant be cropped. If I had centered the framing on either player, I wouldnt have the shot I wanted.

Of course, since I am still bungling the AF, I still dont have that one!

more practice for me! As JoN said, at least it wasnt film I was burning! now I can just charge the batteries and go practice
03-18-2007, 10:00 PM   #13
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The first thing I did on my K10D was to de-couple the AF from the shutter button - that is what the AF button is for. I set the AF select points to center - pick the focus point - focus - compose and shoot.
Having the AF refocus everytime I press the shutter is one of the most irritating aspects of all cameras with AF built in. I de-coupled the AF on my *ist Ds too - it is now the OK button.
I do not like letting the camera computer select what it thinks my subject is - I choose - you know the 5lb protein based computer looking through the lens?
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03-19-2007, 12:11 AM   #14
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QuoteOriginally posted by PDL Quote
I de-coupled the AF on my *ist Ds too - it is now the OK button.
PDL
I am not at home at the moment to check my manual or camera for that matter, but is this an easy process to do on the *ist DS? I'd like to give it a try.
03-19-2007, 12:14 AM   #15
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QuoteOriginally posted by troywhite Quote
I am not at home at the moment to check my manual or camera for that matter, but is this an easy process to do on the *ist DS? I'd like to give it a try.
I think it is the same way I use AF as I posted earlier. Menu > Swtch Dst Msr Pt > (Second option). This way you choose the AF point. The camera doesn't do this for you.
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