Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,226   Posts: 1,532,671   Online: 810
      
Page 1 of 2 12 LastLast
Results 1 to 10 of 13
  1. #1
    Falkenberg's Avatar
    Join Date
    Sep 2007
    Location
    Denmark
    Shooter
    8x10 Format
    Posts
    469
    Blog Entries
    11
    Images
    7

    How to calculate distance from shutter to film ?

    In my planning of making a 8x10 portrait camera I have run into some roadblocks. I have found several webpages that can calculate my front and rear focus distance at any given aperture. My question is how to calculate the distance from the lens/shutter to the film/ground glass plane. I was thinking about making a cardbox camera to have something to test the distance, but since I dont have a ground glass yet, I will not be able to see any changes.

    TIA.

    Best regards
    Mikkel

  2. #2
    Ty G
    You would first need to know the focal length of the lens you are using and build the camera to that. You can figure it out without the ground glass; take a cardboard box, cut a hole in the front bigger than the lens, and cut a hole at the top so you can look inside the box. Aim to a bright object and while looking inside your box, move the lens back and forth 'til focused. Then measure that distance. You can do the same for far objects and very close objects to get the whole range.

    Ty Guillory
    www.tystintypes.com

  3. #3
    Falkenberg's Avatar
    Join Date
    Sep 2007
    Location
    Denmark
    Shooter
    8x10 Format
    Posts
    469
    Blog Entries
    11
    Images
    7

    this lens and shutter

    The Lens is a 240mm/f5.6 with a separate shutter. How would I calculate the distance with this information ?

  4. #4

    Join Date
    Jun 2007
    Location
    Portland Oregon
    Shooter
    Multi Format
    Posts
    137
    Images
    1
    Focus at infinity is 240mm from the nodal point to the film. But portrait's the person is not at infinity so the lens will be farther away from the film plain. If you have a 4x5 view camera just mount it and focus at the distance your subjects will be at and measure. Other wise a high school or first year college physics text book should have all the formulas in it.
    It's not the camera......

  5. #5
    BradS's Avatar
    Join Date
    Sep 2004
    Location
    S.F. Bay Area, California
    Shooter
    Large Format
    Posts
    3,981
    for lenses of conventional design, the formula is:

    1/f = 1/a + 1/b

    where:
    f is the focal length of the lens
    a is the distance from the film plane to the front surface of the lens board (roughly and subject to some assumptions about lens design) and,
    b is the distance from the front of the lens board to the plane of sharp focus (the subject).

  6. #6
    Falkenberg's Avatar
    Join Date
    Sep 2007
    Location
    Denmark
    Shooter
    8x10 Format
    Posts
    469
    Blog Entries
    11
    Images
    7

    Math

    Does this mean that with the 240 mm lens and a person at 3 meters (3000 mm) it would give me a distance 260,86mm from lens to film. Is this correct ? If this is true why are the dedicated portrait 8x10 cameras so huge ?

  7. #7

    Join Date
    Mar 2005
    Shooter
    Multi Format
    Posts
    3,358
    They don't use lenses that are wide angle on the format, they use lenses that are long on the format.

  8. #8
    BradS's Avatar
    Join Date
    Sep 2004
    Location
    S.F. Bay Area, California
    Shooter
    Large Format
    Posts
    3,981
    Quote Originally Posted by Falkenberg View Post
    Does this mean that with the 240 mm lens and a person at 3 meters (3000 mm) it would give me a distance 260,86mm from lens to film. Is this correct ? If this is true why are the dedicated portrait 8x10 cameras so huge ?
    Yes. Substituting the values in your example, I get...

    distance from lens to film = 1 / ((1/240) - (1/3000)) == 260.87 mm

    and as Dan has already pointed out, the 240mm focal length would not normally be considered for portraits with an 8x10 camera. It would likely be considered much too short a focal length for such a task. Also, most LF portaitist that I've encountered seem to prefer to position the camera about a meter from the subject.

  9. #9
    Falkenberg's Avatar
    Join Date
    Sep 2007
    Location
    Denmark
    Shooter
    8x10 Format
    Posts
    469
    Blog Entries
    11
    Images
    7

    wich lens

    For my project the 240mm will have to do, but wich lens should I be looking for to get the best portraits with my portrait camera ? I guess that the distance from camera to the person will be something like 1,5 to 3 meters. I want to fill the frame with the head and a little of the shoulders and neck.

  10. #10

    Join Date
    Dec 2004
    Shooter
    Multi Format
    Posts
    2,146
    Quote Originally Posted by Falkenberg View Post
    For my project the 240mm will have to do, but wich lens should I be looking for to get the best portraits with my portrait camera ? I guess that the distance from camera to the person will be something like 1,5 to 3 meters. I want to fill the frame with the head and a little of the shoulders and neck.
    To fill the frame with head and some shoulders with my appr. 440mm portrait lenses on 8x10", the lens sits less than 1 metre from the nose of my subject and have about 600mm bellows draw. (all estimations, I don't actually measure that when doing)

    I'd advise a slightly longer lens.

Page 1 of 2 12 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin