Sigma 170-500mm f/5-6.3 DG APO concerns

Discussion in 'Photography Beginners' Forum' started by davebmck, Mar 10, 2008.

  1. davebmck

    davebmck TPF Noob!

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    I bought this lens this weekend to use on my Rebel XTi. I want to use this lens mostly for photographing wildlife. I took about 60 shots with it this weekend to see what kind of pictures I can get out of it. The problem I am having is that I can’t seem to get good sharp images at anywhere near the full zoom. I do get good sharp, well focused images at 170mm, but that is not why I bought the lens.

    I’m not a pro photographer and this is my first telephoto lens over 200mm, so I am not sure if the problem is me or the lens. I was shooting in good daylight at iso 400, F8 (which is supposed to be the sweet spot for this lens), distances from 25 to 100 feet, using a tripod and remote shutter release. Shutter speeds ranged from 1/250 to 1/1000.

    When I open the images in Camera Raw they look OK at the default 21% zoom ratio, not perfectly sharp, but respectable. However, when I zoom to 100% the image is not sharp and seems not perfectly focused. Sharpening the image doesn’t completely fix the problem.

    Am I expecting too much from a telephoto zoomed to 500mm or is this lens just not capable of taking sharp images at this setting? I have 10 days to return this lens, and I am currently disappointed enough with it to return it. I just want to make sure it is not what I am doing or that I have expectations that are beyond what is capable with a 500mm lens.
     
  2. GTHill

    GTHill TPF Noob!

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    Are you on a tripod? I would try it on a tripod and use the timer to make sure it isn't camera shake that you are seeing.

    Gene
     
  3. Big Mike

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

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    Also, it's a good idea to use MLU (mirror lock up) when shooting a long telephoto on a tripod.

    Does that lens have OS (stabilization)? If so, you will want to turn it off when using it on a tripod.
     
  4. Mav

    Mav TPF Noob!

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    Yeah what Mike said. You need a camera with a MLU or at least a shot delay after the mirror opens before it starts taking the photo. Otherwise you're probably getting mirror vibrations into your shot.
     
  5. Mystwalker

    Mystwalker TPF Noob!

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    Can IR (OS for Sigma?) help with the mirror vibration if hand holding?

    Maybe my 70-200 isn't considered long enough because I'm not seeing this problem.
     
  6. davebmck

    davebmck TPF Noob!

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    Yes, as mentioned above I am using a tripod and a remote shutter release.
     
  7. davebmck

    davebmck TPF Noob!

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    Good suggestion. I will try it with the MLU the first chance I get. No, it does not have OS. Do you thing manual focusing would help?

    Thanks, Dave.
     
  8. davebmck

    davebmck TPF Noob!

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    My other lens is the Sigma 18-200mm with OS. I get very sharp images with it when hand holding at all focal lengths.
     
  9. Mav

    Mav TPF Noob!

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    Not for this, no. OS/VR/IS/VC (<-- Tamron) only stabilizes the lens, not the camera body. And the support system stabilizes the body/lens combo as a whole. The MLU allows vibrations within the body itself to stabilize before the picture is snapped. You only need to worry about this once you start getting to pretty serious tele lengths and at relatively slow shutter speeds.
     
  10. davebmck

    davebmck TPF Noob!

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    Update. This afternoon I tried manual focus and activating the mirror lock. I didn't see much difference with the manual focus, but the mirror lock up seems to have helped some. My tripod is definitely not up to the job. There was a slight breeze blowing and I could see it causing the camera to shake at 500mm. I had to wait for breaks in the breeze to take shots. Anybody got a suggestion for a solid, stable tripod that doesn't weigh a ton?
     
  11. DSLR noob

    DSLR noob TPF Noob!

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    focusing at the fully zoomed in length isnm't possible. Canon EOS bodies are designed to focus at apertures of 5.6 or larger. A canon EOS 1 series body can manage f/8 or larger, but simply put, if you know the specs of your camera, you know why it doesn't autofocus at 500mm (because it maxes out at 6.3)
     
  12. davebmck

    davebmck TPF Noob!

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    I don't understand what your telling me. I know that the maximum aperture is 6.3 when the lens is zoomed to 500mm, but why wouldn't it be able to focus at smaller apertures, ie F8? Maybe you can explain this differently so that I can understand what you are saying.
     

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