automatic focusing on Rebel 2000 (EOS 300)

Discussion in 'Beyond the Basics' started by ckshen, Apr 26, 2004.

  1. ckshen

    ckshen TPF Noob!

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    when i use the automatic focusing feature on the camera, it focuses. but if i zoom in some more i notice that the image is still a bit blurry so i focus again and then zooms out to my original composition.

    is this the right technique? or should i just stick to the original 'focused' image? does this happen because its supposed to happen or is it because of problems with the lens/body? i am using the cheap 28-80mm that comes with the body.
     
  2. photobug

    photobug TPF Noob!

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    Some zoom lenses have the ability to stay focused throughout the zoom range. I believe the term is "parfocal."

    I wouldn't expect a less expensive lens to have this ability. Try it both ways. If it focuses ok on its own, do it that way. Otherwise the zoom in, focus, zoom out thing, while a PITA, does seem to work.
     
  3. markc

    markc TPF Noob!

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    Thanks Jim. That's something I had wondered myself in the past but never looked up.

    It's probably not parfocal. I just looked up some lenses, and even with the Canons, it's only the fixed aperture L series pro lenses and those with non-rotating front elements. If you focus while telephoto and then put it back to wide-angle, the focus will be off once you move it back. You are best of to focus at the focal length you are going to shoot at.
     
  4. fotoadam

    fotoadam TPF Noob!

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    when it comes to zoom lens, be prepared to spend a lot. I bought a Phoenix 35-300m lens and im EXTREMELY dissapointed. You have to be atleast 6 ft from the subject in low light to get even remotely focused.. i still love my canon 35-80mm lens that came with my Rebel..

    adam
     
  5. Galaxy_Stranger

    Galaxy_Stranger TPF Noob!

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    With a Telephoto, if you zoom in all the way and properly focus on your subject you can zoom strait out and be fine - as long as you're telephoto. Just be careful you don't turn the ring any.

    Besides, your depth of field changes anyway - in fact, you should be able to do the math. Stick it on a tripod and take a couple test shots both ways.

    Am I rambling??
     
  6. markc

    markc TPF Noob!

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    I don't think it works that way. It's not like the focus goes out of whack as soon as you hit 50mm. It's a gradual shift.
     
  7. Galaxy_Stranger

    Galaxy_Stranger TPF Noob!

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    Yeah, I think you're right. But from 150 to 50mm I guarantee you're not gonna see a difference.
     

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