Protar VII mismatched cells

Discussion in 'Large Format Cameras and Accessories' started by Frank R, Oct 6, 2009.

  1. Frank R

    Frank R Subscriber

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    I have shutter that has a Protar VII 14 inch front element and a Protar VII 9 inch rear element.

    Is that correct? I thought the front and rear elements have to match.
     
  2. sanking

    sanking Member

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    Thee front and rear elements of Protar VII convertibles have different focal lengths. This gives three possible focal lengths, of each of the cells when used by itself, and combined.

    Sandy King
     
  3. BrianShaw

    BrianShaw Member

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    I don't know that lens as well as I wish I did, but isn't it a convertable... in which case the front and rear cell are expected to be different. What does the aperture scale look like -- one set of numbers or three sets?
     
  4. David Lindquist

    David Lindquist Subscriber

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    Both Bausch & Lomb and Zeiss made Protars could be bought with the front and back cells the same focal length or with the two cells of two different focal lengths. On the Zeiss made Protars I've seen with the front and back cells the same focal length, the cells had consecutive serial numbers. Based on some information on Zeiss made Protars I have, the equivalent two focal lengths of the two cells you have (22 and 35 cm) combined give a focal length of 15.5 cm.
    David
     
  5. colrehogan

    colrehogan Member

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    I have seen threads like this on the LF forum. I have a CZJ Protar VII in which both elements are 69 cm. However, the serial numbers on each element are different (but sequential- I think).
     
  6. Frank R

    Frank R Subscriber

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    I expected it to be a convertible but it has only one aperture scale on it.
     
  7. Frank R

    Frank R Subscriber

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    This is a B&L lens with a Century (CCC) shutter.

    The front number is 78342

    The front number is 81381



    Thanks, I was going to ask that question next.


    Now, if my shutter has one aperture scale, how do I use these lenses?
     
  8. Frank R

    Frank R Subscriber

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    This leads me to wonder about the coverage. I thought this would cover 8x10, maybe even 11x14 but that 22 cm and 15.5 cm have me thinking it won't cover with those elements.
     
  9. Frank R

    Frank R Subscriber

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    Thanks for the feedback. Any answers to the follow-up questions?
     
  10. roodpe

    roodpe Member

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    Frank,

    Does your aperture scale show fstops? If so, the widest aperture for the combined set would be 7.7. It would be 12.5 for a single element.

    For protar lenses, the manufacturers occasionally also supplied a single scale that gives the diameter of the iris opening. They did this because you can easily calculate the needed iris opening for a given fstop for any combination of these lenses. To do so, you focus the camera, then measure the distance from the center of the lens (iris location with both elements) to the inside face of the ground glass (film plane). Divide this measurement by the desired fstop and you will have the size of the iris opening needed for that fstop. Bellows factor correction is automatic with this method.

    I have attached a file that shows the various iris openings for desired fstops for the zeiss protar VII's. The iris opening shown corresponds to infinity focus.

    To use the single elements, just place them in back of the shutter/iris.

    Pete
     

    Attached Files:

    Last edited by a moderator: Oct 7, 2009
  11. Frank R

    Frank R Subscriber

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    Thanks Pete.

    It shows a single row of f stops. I think I will take a picture today and post it.

    Thanks for posting the list. I will have to study it.
     
  12. Frank R

    Frank R Subscriber

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    bump for the other questions.
     
  13. roodpe

    roodpe Member

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    The lens is good for 4x5/5x7 at all focal lengths. The 35cm element should cover 8x10. The 22cm and the combined lens won't.
     
  14. Frank R

    Frank R Subscriber

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    Here is the picture I promised. Just one f-stop scale. No 12.5

    How can I use this one scale for three different lenses?
     

    Attached Files:

  15. roodpe

    roodpe Member

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    The fstops on the shutter are for the using the lens with both elements attached. You can calibrate ftops for using the single element lenses from the chart I attached by matching the iris opening dimension you would get for the combined lens to that which you need for the single elements.

    For the combined lens, f7.7 has a 17mm iris opening. f45 has a 3mm iris opening. You can get the iris opening size for stops between f45 and f7.7 from the chart. Then go to the section that says "Protar Lens". This gives the iris openings for the single elements. For the 22cm element, f12.5 has an 18mm iris opening. Therefore, you can set the fstop scale on the shutter to f7.7 to shoot at f12.5 with the 22cm element. To shoot the 22cm element at f45, set the iris between f22 and f32 (closer to f32). This will give an iris opening of 5mm. You can use the 35cm element in a similar fashion. For the 35cm lens, you will be limited to stops between f22 and f45 within the scale limits, but this is no problem since you have to stop down the single elements to get decent performance anyway. You can make a chart to help you remember the correct positions. Just remember to put the single element at the back of the shutter, behind the iris.
     
  16. Frank R

    Frank R Subscriber

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    Thanks Pete. I was thinking about making a small chart too.

    This must be a real early Protar since it does not have anything Zeiss on it. Or it was after WWI when they no longer used the Zeiss name. But not having the three scales on the shutter is odd.
     
  17. roodpe

    roodpe Member

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    It was not made by Zeiss. B&L licensed the Zeiss patent and manufactured the lens in the US. B&L used english units (inches) for focal lengths. Zeiss used mm or cm for their lenses. For practical purposes, they are the same. There is a thread on the LF forum regarding B&L serial numbers and date of manufacture.
     
  18. Steve Hamley

    Steve Hamley Member

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  19. goamules

    goamules Member

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    Actually, as I understand it the Protar VIIa is any convertible made up of two Protar VIIs. If they are the same focal length, it's an F6.3 Protar VIIA. If they are two different VIIs, it's still a VIIa, but will be F7 or F7.7. I just figured this out when I bought my first VIIa....

    Garrett