Help me please, poor image quality??

Discussion in 'Digital Discussion & Q&A' started by gators12707, Mar 31, 2010.

  1. gators12707

    gators12707 TPF Noob!

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    Hey everyone, I'm having a pretty annoying problem that I've just begun to notice recently

    I have a Nikon D90 and with my 18-105 kit lens, it seems the pictures aren't coming out sharp or clear at really anywhere around the sides. I know lenses tend to lose quality around the edges, especially at wide zooms, but come on, not this bad.

    I am concerned, does this mean my af motor and/or lens is damaged??

    This was taken with an F/8 aperture (is it just not narrow enough maybe?) at 1/1250 (so the blur isn't camera shake) at ISO250 in af mode, M, with VR on.

    [​IMG]

    Please view the full size.

    Look at the entire left side of the image! including the asphalt, and everything from the left side down, especially the back wheel. Why is this happening? Is it really just that f/8 actually isn't enough? I find that hard to believe with the asphalt so close to the focus point, which is right in the center of the image.

    The most disturbing is the quality of the road to the left side of the image around the sig.
    I tried a bit of unsharp mask, but no good.
     
  2. DScience

    DScience No longer a newbie, moving up!

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    f/8 doesn't allow a great enough DOF to have the whole care in focus from the distance you are shooting at.
     
  3. Big Mike

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

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    That does look odd. :scratch:
     
  4. KmH

    KmH Helping photographers learn to fish Supporting Member

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    According to DOFMaster.com, a Nikon D90 with a lens at a 39 mm focal length (from your EXIF data) and an aperture of f/8 and with the focal point 10 feet from the camera the DOF would be:

    Depth of field
    Near limit 7.6 ft
    Far limit 14.6 ft
    Total 7.04 ft

    In front of subject 2.4 ft (34%)
    Behind subject 4.63 ft (66%)

    If you were closer than 10 feet the numbers get even smaller.

    DOF is effected by more than just the aperture. It is also effected by focal length, subject to image sensor distance and subject to background distance.

    However with all that it looks like zoom blur to me. aAs if you just barelay nudged the zoom ring during the exposure. It's also blurred on the right but it is less noticeable.
     
  5. gators12707

    gators12707 TPF Noob!

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    This is very strange.

    When I look through the viewfinder, the areas around the edges are blurred at 18mm. Even worse, the leftmost af point doesn't seem to work... the focus light just flashes rapidly and intermittently, like it can't find a focus point. But if I zoom to like 50mm and zoom out again, the problem goes away. Maybe just coincidence?

    And here, look at this for comparison from my photography site. It's a multiple exposure but the smallest original aperture was f/6.3:

    [​IMG]

    PS- Ok, this was probably a bad example, but it's the only similar picture I have on this computer
     
    Last edited: Mar 31, 2010
  6. gators12707

    gators12707 TPF Noob!

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    Wow that makes a lot of sense, so maybe that's why the last picture is better, because I was farther away. But that doesn't explain the asphalt.

    And is it even possible to nudge the zoom ring at 1/1000th of a second?
     
    Last edited: Mar 31, 2010
  7. KmH

    KmH Helping photographers learn to fish Supporting Member

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    Sure, if the zoom ring is already moving as the shutter opens and closes.

    If you want, send the lens off to Nikon and get it checked out. I send my camera bodies and lenses in at least once every 2 years for cleaning and inspection.

    How old is your lens?
     
  8. gators12707

    gators12707 TPF Noob!

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    I just got the camera and kit lens 2 months ago :(

    I'll pay extra attention to where my hands are the next couple times I take pictures. Thanks for the advice.

    Btw, how did you pull my exif info? Because I always bracket 3 exposures of my car shots to make sure I have something to work with in case I make a mistake, and the according to the image data in my camera all 3 shots of that car were taken at 26mm, all at F/8, with shutters 1/640, 1250, and 2500. Since the zoom info is 26mm for all 3 shots, and the image I used was the first, isn't it then safe to assume that the zoom ring didn't move?

    by the way, according to dof master, at 26mm, i get

    Subject distance 10 ft

    Depth of field
    Near limit 5.83 ft
    Far limit 35.1 ft
    Total 29.3 ft

    In front of subject 4.2 ft (14%)
    Behind subject 25.1 ft (86%)

    Which is more, right? lol
     
  9. KmH

    KmH Helping photographers learn to fish Supporting Member

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    I just right clicked on the image here in the forums and used my EXIF reader (Opanda) to look at the data.

    Your lens was set to 26mm but on a crop sensor camera (x1.5) it gives the FOV (Field-Of-View) a 39mm lens would give on a full frame camera.

    I should have used the 26mm focal length at DOF Master because I had already selected the D90 family of cameras.

    Your lens is under warranty, so sending it in won't cost you anything.

    Were you 10 feet from the focal point? Or 8 feet, or 11.5 feet?
     
  10. gators12707

    gators12707 TPF Noob!

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    Haha I was probably ~8 feet away.

    I could send it in, but I really don't have the time or the patience to wait, my 50mm really doesn't cover as much as it used to.

    Thank you for being so helpful

    Oh one more question... according to the online dof calculator, with 18mm at 60+ feet away you get infinite dof focus at f/1... is that right? I was always under the impression that shots like that (landscape shots, etc) require a narrow aperture. Am I misunderstanding the calculator?
     
    Last edited: Mar 31, 2010
  11. Flash Harry

    Flash Harry TPF Noob!

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    Kit lens are not reknowned for sharpness throughout the range, either aperture or zoom, they are a compromise and different lenses of the same focal length/aperture can vary greatly, if you want the best stick with primes. H
     
  12. gators12707

    gators12707 TPF Noob!

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    I'm going to try and take some more pictures in the next few days with narrower apertures and see if it helps. Thanks.
     

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