Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,908   Posts: 1,556,009   Online: 1128
      
Page 2 of 2 FirstFirst 12
Results 11 to 16 of 16
  1. #11

    Join Date
    Jul 2007
    Location
    Netherlands
    Shooter
    Medium Format
    Posts
    5,686
    The "aperture plane"? You mean the one the exit pupil is in? Or the one the entrance pupil is in? Or where the physical diaphragm is?
    None of the three is the correct thing to measure from.

    You need to measure from the rear principal plane. Where that is located (and where the entrance and exit pupils are) depends on the lens design. When data are provided by the manufacturer, they usually state the position relative to other bits of the lens, like the last lens vertex. So you need to do some calculations (involving the exact focal length, not just the nominal focal length) to find a number you can use.

    But that's all too technical. Not practical.
    Cameras have a groundglass screen. Use your eyes.
    Reduce the lens to film distance/bellows draw, until everything starts getting out of focus. Go back a bit, "et voila"! Infinity focus!

  2. #12
    Steve Smith's Avatar
    Join Date
    May 2006
    Location
    Ryde, Isle of Wight
    Shooter
    Medium Format
    Posts
    8,609
    Images
    122
    [QUOTE=CPorter;736422]
    Quote Originally Posted by Gary892 View Post
    155 divided by 25.4 mm/inch = 6 inches-----------locate the aperture plane 6 inches from the film plane and you will have infinity.
    I like imperial measurements as much as most people of my age and over who didn't have the metric system drummed into them at school.

    However, why do a conversion? Why not just use the metric measurement?

    Your conversion has already put it 0.1" out as 155mm is 6.102". 6" is 152.4mm.

    I find that I use imperial for large things like building/restoring houses and metric for smaller engineering work.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  3. #13
    CPorter's Avatar
    Join Date
    Feb 2004
    Location
    West KY
    Shooter
    4x5 Format
    Posts
    1,662
    Images
    24
    Quote Originally Posted by Q.G. View Post
    The "aperture plane"? You mean the one the exit pupil is in? Or the one the entrance pupil is in? Or where the physical diaphragm is?
    None of the three is the correct thing to measure from.
    Well, I'm not going to pretend to know the ends and outs of lens construction and lingo--it's more than I care to think about. I can only tell you that I measure from where the aperture is and it works beautifully.

  4. #14
    CPorter's Avatar
    Join Date
    Feb 2004
    Location
    West KY
    Shooter
    4x5 Format
    Posts
    1,662
    Images
    24
    [QUOTE=Steve Smith;736541]
    Quote Originally Posted by CPorter View Post
    Why not just use the metric measurement?
    IDK, I get there just the same and without delay.

  5. #15
    EASmithV's Avatar
    Join Date
    Aug 2008
    Location
    Maryland
    Shooter
    Multi Format
    Posts
    1,877
    Blog Entries
    4
    Images
    123
    When I wanted to find out where my lens was when focused at infinity, I took it outside at night and focused on some stars...

  6. #16
    CPorter's Avatar
    Join Date
    Feb 2004
    Location
    West KY
    Shooter
    4x5 Format
    Posts
    1,662
    Images
    24
    Quote Originally Posted by EASmithV View Post
    When I wanted to find out where my lens was when focused at infinity, I took it outside at night and focused on some stars...
    I simply found the distance from lens to film plane by measuring with a ruler just once, then noted the distance in mm from inside to inside of the front and back standards. Anytime I want infinity, I simply separate the standards by 126mm inside to inside on the monorail------very quick.

Page 2 of 2 FirstFirst 12


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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