Site Sponsors
Results 1 to 3 of 3

Thread: Alpa Cameras: Image circle and focus

  1. #1
    Member
    Join Date
    Jul 2009
    Posts
    206
    Post Thanks / Like

    Alpa Cameras: Image circle and focus

    I'm wondering how the image circle of a lens relates to where the lens is focused in the scene. For example, a lens might have an image circle of 189 at F22 and focused at infinity. But what kind of image circle might that same lens have when focused at moderate distances or close focus distances? Thanks for any insight

  2. #2
    Workshop Member
    Join Date
    May 2008
    Location
    NYC
    Posts
    3,275
    Post Thanks / Like
    Images
    7

    Re: Alpa Cameras: Image circle and focus

    Quote Originally Posted by Mike M View Post
    I'm wondering how the image circle of a lens relates to where the lens is focused in the scene. For example, a lens might have an image circle of 189 at F22 and focused at infinity. But what kind of image circle might that same lens have when focused at moderate distances or close focus distances? Thanks for any insight
    Image circle (as seen by the sensor) increases in size at closer distances, though you won't notice a large difference until you get towards macro.

    Think of the lens as a fixed element* in the universe - it doesn't move and the the cone of light it projects doesn't change. However when focusing closer than infinity the sensor is further away from the lens and therefore further away from the "tip" of the cone of light and therefore sees a larger image circle.

    *no pun intended

    Doug Peterson (e-mail Me)
    __________________
    Head of Technical Services, Capture Integration
    Phase One, Leaf, Cambo, Canon, Apple, Profoto, Eizo & More
    National: 877.217.9870 *| *Cell: 740.707.2183
    Newsletter: Read Latest or Sign Up
    RSS Feed: Subscribe
    Buy Capture One at 10% off
    Personal Work

  3. #3
    Member
    Join Date
    Jul 2009
    Posts
    206
    Post Thanks / Like

    Re: Alpa Cameras: Image circle and focus

    Thanks Doug, that's similar to what I was thinking but just wanted to make sure....thanks again

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •