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FORUMS Canon Cameras, Lenses & Accessories Canon EOS Digital Cameras 
Thread started 06 Apr 2009 (Monday) 21:07
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Rebel XSi AF issue

 
Exposure101
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Apr 06, 2009 21:07 |  #1

I've searched but couldn't find a thread that answered my question so here's a new one for you guys. :D

When focusing on a point (person, face, tree, etc.) sometimes I would have to half-press the shutter button several times before the red dot would light up indicating the correct part that I want to focus on. When using the Canon 24-70mm lens I had trouble using the AF point all the way to the right. For example, when taking portraits I would like that point to focus on the face and that means pressing the button a bunch of times before the red dot lights up (10-15 times).

When using the kit lens (18-55 IS) I noticed that it was easier but I would have to move the camera so that it could "pick up where I want it to focus on." At first I thought it was the lens but it might just end up being the camera. Any thoughts/comments is appreciated!




  
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Colors
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Apr 06, 2009 21:23 |  #2

things that you might have quickly looked over:
are you in AI servo or manual focus? what kind of lighting conditions? which focus points?


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Canon ­ Guy
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Apr 06, 2009 21:57 |  #3

Are you having trouble focusing or is it simply not selecting the right focus point?


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Lazuka
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Apr 06, 2009 22:04 |  #4
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how close are you to the subject?


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Exposure101
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Apr 06, 2009 22:05 |  #5

Colors wrote in post #7681622 (external link)
things that you might have quickly looked over:
are you in AI servo or manual focus? what kind of lighting conditions? which focus points?

I used "one shot AF" and used to shoot at night. However, it's not just at night or in the shade. Is the problem because I used ONE SHOT instead of AI servo? It's usually the one all the way to the right when the camera is being held regularly (horizontally).

Canon Guy wrote in post #7681823 (external link)
Are you having trouble focusing or is it simply not selecting the right focus point?

The latter. It sometimes would not focus on the correct point(s) and I would have to keep pushing the button in order to find the correct one(s).

Lazuka wrote in post #7681863 (external link)
how close are you to the subject?

Usually about 5-10 feet. Sometimes when I take things in macro mode it would happen too.




  
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Brett
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Apr 06, 2009 22:23 |  #6

You're letting the camera select your AF point. Do it yourself. The camera has no idea that you intend a certain point to be the point-of-focus, so it guesses. It often seems to choose whatever's nearest the camera, but not always.

Manually select the point you want to use, and this issue will disappear. :)



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Canon ­ Guy
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Apr 06, 2009 22:27 |  #7

Exposure101 wrote in post #7681875 (external link)
The latter. It sometimes would not focus on the correct point(s) and I would have to keep pushing the button in order to find the correct one(s).

As long as you're not shooting in Auto, you can manually select your focus points by hitting the the button at the top right of the camera (beside the * button) and then using the scroll wheel.


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MX-ActionShots
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Apr 06, 2009 22:29 |  #8

Brett wrote in post #7681982 (external link)
You're letting the camera select your AF point. Do it yourself. The camera has no idea that you intend a certain point to be the point-of-focus, so it guesses. It often seems to choose whatever's nearest the camera, but not always.

Manually select the point you want to use, and this issue will disappear. :)

Yup! Do it manually by :
turn camera on- press the magnifying button and then select what focus point you want to use and hit set.


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Exposure101
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Apr 06, 2009 22:48 |  #9

Yeah I did use MF but sometimes I need to focus on more than one point. Is it possible to manually select more than one point?




  
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roastpuff
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Apr 07, 2009 00:18 |  #10

Exposure101 wrote in post #7682102 (external link)
Yeah I did use MF but sometimes I need to focus on more than one point. Is it possible to manually select more than one point?

Nope. Not possible with any other camera I've tried or any on the market I think, because there can only be one focus (since you only have one lens!). Use a higher f-stop in order to retain more area in focus.

Typically the object of desired focus is in the middle of the frame, that's why the camera tends to guess in the middle and from there go on to other possible focus points. You should always select the point manually using the focus point select button then using the dial to rotate through them. It's a hassle but that's how it's done.




  
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Exposure101
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Apr 07, 2009 01:09 |  #11

Thanks for the replies guys! I guess there's just no way around it. I thought since they're supposed to be more accurate that they would work better.




  
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roastpuff
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Apr 07, 2009 01:33 as a reply to  @ Exposure101's post |  #12

They are more accurate... they're just not mind-readers. ;)




  
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Brett
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Apr 07, 2009 12:17 |  #13

Exposure101 wrote in post #7682657 (external link)
Thanks for the replies guys! I guess there's just no way around it. I thought since they're supposed to be more accurate that they would work better.

They can't "work better" when the camera doesn't know what you want to focus on. On a P&S camera, the depth-of-field is usually so large that as long as the camera acquires focus on something in the scene, everything else will be in focus as well. If you want that, shoot at f/16 or so.

And by saying the focus points are "more accurate", people mean that the point that's selected more accurately focuses that point. Not that the camera is reading the user's mind concerning what they wish to focus on.



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Dick ­ Z.
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Apr 07, 2009 16:08 |  #14

Exposure101 wrote in post #7681516 (external link)
I've searched but couldn't find a thread that answered my question so here's a new one for you guys. :D

When focusing on a point (person, face, tree, etc.) sometimes I would have to half-press the shutter button several times before the red dot would light up indicating the correct part that I want to focus on. When using the Canon 24-70mm lens I had trouble using the AF point all the way to the right. For example, when taking portraits I would like that point to focus on the face and that means pressing the button a bunch of times before the red dot lights up (10-15 times).

When using the kit lens (18-55 IS) I noticed that it was easier but I would have to move the camera so that it could "pick up where I want it to focus on." At first I thought it was the lens but it might just end up being the camera. Any thoughts/comments is appreciated!

If you get to close or out of close focus range the camera will not focus and better still the shutter will not trip, at least my XSi works that way with any lens I have.:confused:




  
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Rebel XSi AF issue
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