Re: Field of view - need help with the math

Discussion in 'Digital Photography' started by David Dyer-Bennet, Nov 15, 2011.

  1. Signet <> writes:

    > I respectfully beg to differ. Using the diagonal of the frame
    > size for the normal focal length was conceived of as a rule-of-
    > thumb, not really scientifically. My first camera was a Pony 135
    > and it had an f/3.5 44mm lens. It was decidedly moderately wide-
    > angle. A later precision camera, a Minolta SR-1 featured a
    > correct 55mm f/2. Minolta wisely chose that focal length because
    > it provided a 1:1 image in the viewfinder. In other words, if
    > you viewfind the focused subject with your left eye and
    > simultaneously sighted the same subject with your naked right
    > eye, the two images are coincident. Thus, the field of view of
    > the camera and eye are the same to the limits of the frame,
    > which is the real definition of a "normal" focal length. Sadly,
    > fixed 55s are next to impossible to find these days.


    But that's not field of view you're comparing; that's magnification.
     
    David Dyer-Bennet, Nov 15, 2011
    #1
    1. Advertising

  2. David Dyer-Bennet

    Peabody Guest

    David Dyer-Bennet says...

    > But that's not field of view you're comparing; that's
    > magnification.


    To be clear, I want to take "the same picture" with my T2i
    as with the Medalist. So I'm looking for the same field of
    view.

    I think my 26.4mm number was right. It's kinda hard to tell
    by looking through the Medialist viewfinder because I don't
    know what percentage of the actual field shows up in the
    viewfinder. But it does look pretty close.

    Well, I bought a roll of film today, so I'll know soon
    enough, assuming the respooling goes ok.
     
    Peabody, Nov 16, 2011
    #2
    1. Advertising

  3. In article <>, Peabody
    <> writes
    >David Dyer-Bennet says...
    >
    > > But that's not field of view you're comparing; that's
    > > magnification.

    >
    >To be clear, I want to take "the same picture" with my T2i
    >as with the Medalist. So I'm looking for the same field of
    >view.
    >
    >I think my 26.4mm number was right. It's kinda hard to tell
    >by looking through the Medialist viewfinder because I don't
    >know what percentage of the actual field shows up in the
    >viewfinder. But it does look pretty close.
    >

    Fortunately both the sensors are 3:2 aspect ratio so it doesn't matter
    what dimension you use, provided you use the same on both. The posts
    about image diagonal are just irrelevant in this case.

    Your Medalist has sensor width of W1, sensor height of H1, sensor
    diagonal D1 and focal length F1. Your T2i has sensor width of W2,
    sensor height of H2, sensor diagonal D2. You are trying to find focal
    length F2.

    F2 = F1 x W2 / W1 = F1 x H2 / H1 = F1 x D2 / D1 = approx. 26.4mm
    as you first estimated.

    If the aspect ratio of the sensors was different then you would need to
    decide which FoV you wanted to be the same - horizontal, vertical or
    diagonal - they would all be different.

    However, you may well find that the focal length of the lens on your
    Medalist is only nominally 100mm, and could have a tolerance of as much
    as +/-10% which might even change with ambient temperature. Your
    required focal length will have the same tolerance.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Nov 16, 2011
    #3
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. mary wei

    - Need math help on toner coverage

    mary wei, Aug 28, 2003, in forum: Computer Support
    Replies:
    33
    Views:
    5,072
    Mr. Smiley
    Sep 7, 2003
  2. Alan F Cross
    Replies:
    5
    Views:
    401
    Bernhard Mayer
    Aug 13, 2003
  3. Doug Mitton

    View Finder vs. Image Field-Of-View!

    Doug Mitton, Dec 13, 2004, in forum: Digital Photography
    Replies:
    6
    Views:
    437
    Matt Ion
    Dec 14, 2004
  4. Chris
    Replies:
    3
    Views:
    402
    Chris
    Nov 30, 2007
  5. Peabody

    Field of view - need help with the math

    Peabody, Nov 13, 2011, in forum: Digital Photography
    Replies:
    3
    Views:
    307
    Kennedy McEwen
    Nov 16, 2011
Loading...

Share This Page