Close
Close
  1. #1
    SixTwoImages is offline I'm new here!
    Join Date
    Sep 2009
    Posts
    8

    Default How Far Is 50mm, 200mm, 400mm, Etc??

    If I know how far away I will be from a given subject and know what framing I am looking for... How do I convert that to lens length?

    I usually shoot with a Nikon 18-200 which has great range for most of my shots, but recently I was at the local aquarium and was on the opposite side of the sea ray display from my wife and baby... This was maybe 60 feet... and the 200mm was just not enough for a tight shot of my wife and baby's reactions

    I would like to plan ahead and bring the correct lens for what I will be shooting.


    This would also be helpful when I know how far away I will be from the subject at concerts, sporting events, and the like.

    Any help on this would be very appreciated.

    Thanks

    SixTwoImages
    Atlanta GA

    EDIT

    I'm thinking I asked the question incorrectly... or maybe I made it to complicated.

    IF I have a subject framed with a 50mm lens 10' from the camera, and I was to move to 100' away from the subject... What lens focal length would I need to accomplish the same framing?
    Last edited by SixTwoImages; 01-20-2010 at 01:44 AM.

  2. #2
    firebox40dash5 is offline dPS Forum Member
    Join Date
    Nov 2009
    Location
    OR
    Posts
    143

    Default

    The only easy way that comes to my mind would be to do the math with your distance from a subject (the radius of a circle with the camera as the center and the subject as the perimeter) and the angular field of view. For example, 60' from your subject, a 360 degree FOV would have a circumference of ~377'. Nikon states the FOV of your lens @ 200mm as 8 degrees. So your FOV would be 377*(8/360), or roughly 8.5' You'd have to make sure to use the DX field of view, as FX/film is wider- the 200mm f/2 tele has a stated FOV of 12 degrees, 20 minutes.

    Edit: Now I'm doubting myself whether it's the arc of that circle, or a flat plane. If it's a flat plane, you can either calculate the chord of that arc, or take half the angle and use tan(angle of view)=((1/2 the width)/(distance)). That works out to about 8.4'. It won't be precise (due to your subject being calculated on the perimeter, not the chord), but gives you a rough idea.
    Last edited by firebox40dash5; 01-19-2010 at 06:03 AM.

  3. #3
    RichardTaylor is offline dPS +1000 Club
    Join Date
    Nov 2009
    Location
    Sydney, Australia
    Posts
    7,829

    Default

    This will help. Just scroll down to the Dimensional Field of View Calculator

    http://www.tawbaware.com/maxlyons/calc.htm

  4. #4
    SixTwoImages is offline I'm new here!
    Join Date
    Sep 2009
    Posts
    8

    Default

    I just blew a blood vessel on that one...

  5. #5
    RichardTaylor is offline dPS +1000 Club
    Join Date
    Nov 2009
    Location
    Sydney, Australia
    Posts
    7,829

    Default

    Glad to help out!

  6. #6
    OsmosisStudios's Avatar
    OsmosisStudios is offline Don't Panic
    Join Date
    Sep 2008
    Location
    Toronto / Ottawa
    Posts
    12,948

    Default

    Quote Originally Posted by SixTwoImages View Post
    I just blew a blood vessel on that one...
    As long as it wasn't anything more... personal.
    I am responsible for what I say; not what you understand.
    adammontpetit.com
    Gear List
    500PX | Graphic Design

  7. #7
    sk66's Avatar
    sk66 is offline Lovable Contrarian
    Join Date
    Apr 2008
    Location
    Harrisburg, PA
    Posts
    14,972

  8. #8
    firebox40dash5 is offline dPS Forum Member
    Join Date
    Nov 2009
    Location
    OR
    Posts
    143

    Default

    I like Richard's way a lot better than mine! A quick google of "focal length conversion" didn't turn up anything useful for me, though.

    Quote Originally Posted by sk66 View Post
    This is why they make zoom lenses!
    My first thought was "Why do you need to calculate field of view when you're using the lens with the 3rd widest zoom range available?"

  9. #9
    SixTwoImages is offline I'm new here!
    Join Date
    Sep 2009
    Posts
    8

    Default Hmmm..

    I'm not really interested in calculating field of view, or maybe I am and I don't know it...

    I am simply looking for a rule of thumb to decide lens choice when I know distance to subject.

    Thanks everyone..

    RJ

Posting Permissions

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

Log in

Log in