Checking of the calibration of my R3a

Discussion in 'Rangefinder Forum' started by Rom, Nov 1, 2012.

  1. Rom

    Rom Member

    Messages:
    133
    Joined:
    Sep 27, 2010
    Location:
    Lyon - Franc
    Shooter:
    Multi Format
    Dear All,

    I just calibrate this morning my rangefinder on my bessa R3a. I followed the well known article of Arran Salerno .

    To be sure of what i have done, i calibrated the infinity focus on the moon.

    Now, i just check the close focus and:
    - scale focus is at one meter on my lens
    - i have one meter from the point that i focus up to the front of the body's camera (where it's written R3a)
    - and so, i have approximately 103cm up to the film mark

    My worries are i was thinking that the scale focus will give me the exact distance between the subject and the film because, when we focus, we focus on the film.

    If you could drive me, perhaps i am wrong somewhere.

    Thanks in advance
     
  2. nanthor

    nanthor Member

    Messages:
    653
    Joined:
    May 30, 2008
    Location:
    Michigan
    Shooter:
    Multi Format
    I don't think it's possible to be that precise using the markings on the lens, you might be spot on in your close focus. Best way to tell is to take some pictures and see if the camera is close focusing or far focusing. If it's off, and probably not by much, then try to adjust it again to make it spot on for close focus. You can put a ground glass on the film rails or some wax paper to act as a GG, keep the back open and focus on something about 1 meter away with the RF, then check the GG to see if it's in focus. Adjust until you get this spot on. After you get it right, double check your infinity focus. There's a screw that adjusts the difference between infinity focus and close up focus but it is not easy to get to. You have to take the top plate off the camera to get to it. It usually does not need to be adjusted and if it does it's best to leave it to the experts. Good luck, Bob.
     
  3. Rom

    Rom Member

    Messages:
    133
    Joined:
    Sep 27, 2010
    Location:
    Lyon - Franc
    Shooter:
    Multi Format
    Dear Bob,

    Thanks for the input. Indeed i will try within the next roll.

    Thanks

    Rom
     
  4. ic-racer

    ic-racer Member

    Messages:
    7,513
    Joined:
    Feb 25, 2007
    Location:
    Midwest USA
    Shooter:
    Multi Format
    You are checking focus at the film plane right? In that case, you are thinking the lens is engraved wrong?
     
  5. Rom

    Rom Member

    Messages:
    133
    Joined:
    Sep 27, 2010
    Location:
    Lyon - Franc
    Shooter:
    Multi Format
    I am trying to figure if the scale is ok and if my calibration is good or not.

    Anyway i will have to test to be sure.

    What do you know about the scale on the Lens ? Can it be false ?
     
  6. summicron1

    summicron1 Subscriber

    Messages:
    1,992
    Joined:
    Jul 28, 2010
    Location:
    Ogden, Utah
    Shooter:
    Multi Format
    engraving on the lens is not meant to be that precise...look at how thick the lines on the lens scare are -- to precisely indicate the difference between 100 cm and 103 cm they'd have to be a lot finer, the arrow to point to the lines would need to be a lot sharper, and you'd need a magnifying glass to make sure they were properly aligned.
     
  7. rjbuzzclick

    rjbuzzclick Member

    Messages:
    312
    Joined:
    Jan 30, 2010
    Location:
    Minneapolis
    Shooter:
    Multi Format
    Some cameras have a mark on the top plate that shows where the film plane is. It's a flat line with a circle in the middle of it. It's probably 2cm behind the front of the body, so you're probably at least closer than 3cm out. As mentioned above, the best to check alignment is to put a ground glass or frosted tape on the film plane, and check focus there against the rangefinder.
     
  8. ic-racer

    ic-racer Member

    Messages:
    7,513
    Joined:
    Feb 25, 2007
    Location:
    Midwest USA
    Shooter:
    Multi Format
    Yes, you have to check focus at the film plane with a microscope slide and translucent tape or something similar.