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F-Stop and Image Resolution

  1. Oct 17, 2012 #1
    This is a very simple question.

    Does a larger f-stop lead to an image with a higher resolution?

    The reason why I think so is that with a larger f-stop (f-stop=f/D), the focal length will be greater, and because the image height is proportional to the focal length when the object is at infinity, a greater focal length will lead to a larger image. A larger image on the sensor will give a result with higher resolution.

    I'm surprised that I cannot google for a relationship between f-stop and image resolution. Did I make any error in my reasoning?

    Edit: I just found this, and it seemed to confirm my conclusion.
    http://www.marietta.edu/~mcshaffd/macro/terms.html [Broken]
    (See definition for exposure.)
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Oct 17, 2012 #2

    russ_watters

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    Staff: Mentor

    Changing f stop changes aperture, not focal length. And the larger the aperture, the higher the resolution.
     
  4. Oct 17, 2012 #3
    Hmm... I'd argue that the resolution is uniquely defined by the number of CCD pixels. The actual image quality depends on a number of factors. If you're assuming the primary error is due to diffraction, then a larger aperture should give you a better image quality. If it's because the photographer sucks as focusing then you're better off with a smaller aperture.
     
  5. Oct 17, 2012 #4

    russ_watters

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    Staff: Mentor

    Digital and optical resolution are such different things, it doesn't make much sense to mix them together in such a question. Similarly, magnification and resolution aren't the same thing either, so while increased magnification can provide increased digital resolution, it doesn't change optical resolution and the smaller field of view makes the results not directly comparable.
     
  6. Oct 17, 2012 #5

    turbo

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    Gold Member

    Higher f-stop=smaller aperture=increased resolution. Smaller f-stop=larger aperture=lower resolution. Note that DOF (depth of field) decreases with smaller f-stop/larger aperture.
     
  7. Oct 17, 2012 #6

    jbriggs444

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    Science Advisor

    Seems to me that this assumes that the dominant problem with resolution is with focus errors, spherical aberration and chromatic aberration. A smaller aperture can mitigate those problems, making the lens act as a pinhole camera in the small aperture limit.

    If the limit on resolution is due to diffraction or light gathering ability, a larger aperture will do better.
     
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