Parralax Error?????

Discussion in 'Beyond the Basics' started by binglemybongle, Feb 28, 2006.

  1. binglemybongle

    binglemybongle TPF Noob!

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    Hi all,

    Firstly, I'm not sure if that's what it's called. Let me explain.

    I want to use my Rolleicord Vb with close up lenses but as it's a TLR, I know that if i get too close, the image on the film wont be the same as the focusing image.

    How close do you have to be for this to make a difference?

    Obviously a landscape will make no difference.
    Something 50 feet away wont make a difference.
    Something 5-10 feet away, I'm guessing will have a little affect.
    What about somehting 1 foot away???

    Any input will be greatly received.

    Thanks anyone.
     
  2. Hertz van Rental

    Hertz van Rental TPF Noob!

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    It tends to vary with the focal length of the lens.
    Some TLR's have parallax correction scales or guides - I have a Mamiya 330S Pro that has this feature.
    If you don't then there are several ways to deal with it.
    The easiest is to use a ruler.
    Measure the distance between the centre of the two lenses.
    Focus on the subject and do the composition.
    Then raise the height of the camera by the distance measured.
    A tripod with a crank raised centre column is best for this.
    Shoot a test roll first to make sure that you have the measurements right.

    If you are going to do close-ups at a range of distances from the lens, the parallax displacement will vary. Lens/camera manufacturers often do a parallax correction graph so it might be worth doing a search.
    You can construct your own.
    Set up a target that can be easily seen - a strip of white tape across a blackboard for example.
    Position the camera so that the white line is across the centre of the viewfinder.
    Measure the distance between film plane and target.
    Take a picture.
    Repeat the process at different distances.
    Process the negs and measure how much the line is off centre for each distance and plot displacement against distance on a graph.
    Use the graph to predict displacement at a given distance.
    Set the shot up and raise the camera by the calculated amount.
    Do a test shot and see how accurate you are.
    With a little thought and care (and a bit of time and effort) you should be able to produce a workable graph.

    I've had a look through my stuff and can find no easy formula for calculating the displacement.
    I suspect there is one so I shall keep looking.
     
  3. binglemybongle

    binglemybongle TPF Noob!

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    Is it just the difference in height no matter what difference from the subject?

    Does it not get exaggerated the further away you move?

    As in 1 x differnce at a certain distance then x 2 at twice the distance etc?
     
  4. Hertz van Rental

    Hertz van Rental TPF Noob!

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    It varies depending on the focal length of the lens.
    For telephoto lenses it starts to have an effect further away than with a wide.
    I'm looking for a formula....


    **Edit**
    After a lot of cross-checking it would appear that your assumption is quite correct.
    Raising the camera by the distance between the two lens centres does indeed compensate for parallax displacement at all distances.
     
  5. montresor

    montresor TPF Noob!

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    Mamiya made an insert thing for their TLRs, it went on the tripod. You composed your shot, then flipped a lever or something, and the camera raised exactly the height to correct the parallax. Wonder if something like this might be usable on the Rollei. It would have to be adjustable. HvR, any word on this device?
     
  6. markc

    markc TPF Noob!

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    You should be able to find a generic one. And the difference is always the same, which is the distance between the center of both lenses. It's just more noticable up close.
     
  7. Torus34

    Torus34 No longer a newbie, moving up!

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    Let's get practical, shall we?

    I assume you're taking shots from a tripod with an 'elevator' central post. No? Then get a good, cheap, heavy one and use it.

    Next, determine how many turns of the crank are required to move the taking lens into the position of the viewing/focussing lens. My good ol' Star D takes 2 1/2 turns.

    Then focus, crank the tripod and shoot.

    Problem solved.
     
  8. binglemybongle

    binglemybongle TPF Noob!

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    Thanks all.

    I woke up this morning to check TPF and everyones turned into a scientist!

    I may well invest in a sturdier tripod.
    Im going through a phase of upgrading everything and the tripod was down the list but has now been bumped up.

    In combination of this and finally getting a scanner, watch this space for results.
     

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