Questions about my Rebel XT - Focusing & Metering.

Discussion in 'Beyond the Basics' started by SEPhotography, Jul 31, 2007.

  1. SEPhotography

    SEPhotography TPF Noob!

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    SO...I started off shooting in Manual mode, but I don't think I really understood the focusing options of my XT. So I guess I ought to get a handle on them now.

    I don't know why it's so hard for me to comprehend these right now, lol. But I'm having a hard time with the AF Point Selection and locking focus.

    I just don't understand why a lot of times it works and others it can't seem to focus, by going out then in then out and not shooting when it is focused..or like a 2 sec delay.

    And can someone explain back button focusing. I saw it in a thread here but now I can't seem to find it.

    Also, Metering. The XT has Partial Evaluative and Center Weighted. I'd like to try a silhoutte and backlighting, but I can't seem to grasp them.........

    **Eta - sorry I'm getting flustered and annoyed with practicing this today because it just keep slipping from me....., lol**
     
  2. Digital Matt

    Digital Matt alter ego: Analog Matt

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    Ok, lots of questions here.

    The autofocus works by locating areas of high contrast. It's not a 100% accurate technology. There will be times when it fails. In low light, obviously it will have a tough time. Also, the faster the lens you are using, the better the autofocus wil do in low light.

    Back focusing is when a camera or lens (could be a problem of either of both) focuses a tiny bit behind the intended subject. Most times having either the lens or body or both re-calibrated by the manufacturer will cure this problem.

    I don't own an XT, but if you read your manual, I'm sure it will tell you how to set up the back button to operate AF. It is a custom function.

    Understanding how each metering type works is crucial to understanding which one to use in what situation. Again, read your manual and it will explain the different types of metering. For a sillhouette, you want very bright light behind the subject (such as a sunset) and little to no foreground light. If you correctly expose for the light behind the subject you'll create a silhouette. The key is metering the light hitting the background. I would use Center Weighted myself, and pick a spot of the background to meter.
     
  3. Garbz

    Garbz No longer a newbie, moving up!

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    As far as I know that is only the way autofocusing works on P&S cameras which have the image available all the time.
    The biggest downside is it is insanely computationally intensive and thus slow. SLRs use a phase detection system whereby in the pentaprism the image is split in two. The subject is in focus when that point on an image is perfectly aligned with the other image. It works the same way as the split prism manual focusing screens, except that the images are electronically compared, instead of aligned in the viewfinder at one point only.
     
  4. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Welcome to the forum.

    I'd suggest slowing down and trying to learn one thing at a time. If you want to figure out your Auto focus system...then keep the camera in P mode and don't worry about the exposure. When you have the focus down, then start trying modes like Av & Tv. Metering can take some practice, read the manual a few times and then do some other reading (book or web search). Don't be discouraged if you don't get it right away...it often takes a bit of time and patience before things start to 'click', so to speak.
     

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