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PostPosted: Thu Apr 09, 2009 8:16 pm 
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SpartanWarrior wrote:
another thing i wanted to ask you on the AF-Points it seems like with all my lenses when i only choose the center AF-point the pictures are more sharper than when you have all the AF-Points chosen why is that? this is why i always keep the center AF-point chosen;)

That's a tough question! Is anybody here to give SpartanWarrior a cue?
Myself, I'd suspect that more AF-points make the camera do some sort of "average" focussing which is perhaps better on average on all focus points but worse on the single one in the middle.
SpartanWarriors gear is: Canon 40D, Tamron 18-270 VC, Tamron 17-50, Sigma 30 1.4, Canon IXUS 850 IS, PS CS4.

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PostPosted: Thu Apr 09, 2009 8:33 pm 
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Takes the camera longer to focus all the points.
Maybe taking pic too soon while cam is still .."thinking"?

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PostPosted: Thu Apr 09, 2009 8:45 pm 
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I suspect the camera can get confused at times with multi AF points active. There might be something in scene that is more "interesting" to the AF system than the subject you think it should chose. So I find multi point works best in relatively uncluttered scenes or if you are working deep DoF, otherwise I prefer single point.

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PostPosted: Thu Apr 09, 2009 9:35 pm 
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Yeah, same with me, popo!
Using multi-point with lenses up to 50mm, but single-point Af from 50mm on. because you can never trust what the camera decides when no all AF-points can be optimally in-focus.

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PostPosted: Thu Apr 09, 2009 9:56 pm 
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Remember the centre focusing point on many DSLRs is more sensitive or sophisticated than the surrounding ones.


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PostPosted: Fri Apr 10, 2009 6:10 am 
I use just the centre focus point only.


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PostPosted: Fri Apr 10, 2009 6:43 am 
My 450D have 9 AF Point But I usually use a single center AF Point which is more accurate & flexible rather than using Multi AF Point . :)


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PostPosted: Fri Apr 10, 2009 12:57 pm 
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Thanks guys :D i too now always use the center AF point only;)

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PostPosted: Fri Apr 10, 2009 7:52 pm 
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I use center point only, or manual focus.

Not tried a 1D series for the focus selection yet, but my 350D, 40D and 5DMkII all suck and get it wrong most of the time, even when they do lock onto the right focus point, its usually out a little.

If im honest, a couple of times i've switched to manual and done a better job.


Focus and recompose is great for most things, especially if you're pretty fast at it, but for certain things its not any good for like sports, wildlife (to an extent) and macro. For those you can set it to AI Servo and track with the center point only, which is pretty good.

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PostPosted: Fri Apr 10, 2009 8:08 pm 
I switch to the specific AF point closest to my subject if I have the time. For travel photography I found the automatic focus points quite handy - you can work out pretty well how the camera thinks and which point it's most likely to use. and if it doesn't use the one you want, you can always switch to center AF or another one for that matter.

using the center point only + recomposing can lead to significant backfocus (cant be bothered to explain why at the moment, but if you think about it a little, you'll figure it out yourself).


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PostPosted: Sat Apr 11, 2009 2:33 am 
I have found that for me, the center AF point is giving me better results. I find myself locking on to my subject and then slightly panning to frame my shot.

I have been wondering though, does the camera choose exposure off of what that one AF point hits?


I always try to point it on eyes, or lately with my newborn daughter her skin. I was thinking that I want the exposure to be dialed in on her skin tone, but if I point at the eye on someone, does it take exposure off the eye and could make for a over exposed picture?


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PostPosted: Sat Apr 11, 2009 7:37 am 
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Exposure is a different setting and can be set for varying area sizes centred in the middle. If you want you can set exposure lock similar to focus lock before recompose. Doesn't have to be same place either. I very rarely use it but it certainly gives your fingers a workout.

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PostPosted: Sat Apr 11, 2009 12:30 pm 
would I be wrong to ask in this topic:

What is the difference between metering and an AF point?

I kinda thought they worked together, but I am pretty much self taught and have much to learn.


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PostPosted: Sat Apr 11, 2009 12:34 pm 
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AF: focus
metering: light
Different functions, but of course both are important to get the image you want.

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PostPosted: Mon Apr 13, 2009 11:18 pm 
Well, I guess I tend to get confused, because I thought metering takes its measurements from the point off its Auto focus point. Therefore feeling as if they are sort of related to the same exact location it locks onto.

Am I close? Or does the camera meter a different way?

So if I choose center point focus and I focus on a persons black shirt on a sunny day. Will my image be drastically overexposed? If so would a different metering mode help to avoid this?

thanks


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