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Thread: inches vs. f stop dial on conveyable lens

  1. #1

    Join Date
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    inches vs. f stop dial on conveyable lens

    I just bought a beautiful convertible lens from Central Camera in Chicago. It is an Ilex-Calumet Series 8 Caltar. On the aperture ring it has the settings for 4.8 through 45 and a scale marking 8 1/2". Just above this ring is another scale going from 10 to 45. That scale says 14". So I assume the 14" scale is for the lens when used as a 14" lens and the other when used as a 8 1/2" lens.

    Do I simply convert inches to millimeters? So the 14" lens would be 355.6 mm? And the 8 1/2" would be a 215.9 mm lens?

    According to the scale, the 14" scale shows a maximum aperture of 4.8 and the 8 1/2" lens has a maximum aperture of 10. Does this sound like I am understanding this?

    Thanks!

    Alexis
    Alexis

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  2. #2

    Join Date
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    Re: inches vs. f stop dial on conveyable lens

    The lens has two cells, front and rear. When both cells are in the shutter the complete lens' focal length is 8 1/2" = 215 mm and its maximum aperture is f/4.8. In this configuration, use the aperture scale the starts at 4.8.

    The lens is convertible. To convert the lens, remove the front cell. The rear cell's focal length is 14" = 355 mm. Its maximum aperture is f/10. In this configuration use the aperture scale that starts at 10.

  3. #3
    Mark Sawyer's Avatar
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    Re: inches vs. f stop dial on conveyable lens

    Quote Originally Posted by fralexis View Post
    I just bought a beautiful convertible lens from Central Camera in Chicago. It is an Ilex-Calumet Series 8 Caltar.
    Technically, it's a Series S, not a Series 8. A re-branded Ilex Acuton, (single-coated Plasmat design), and a very fine lens!

    Quote Originally Posted by fralexis View Post
    Do I simply convert inches to millimeters? So the 14" lens would be 355.6 mm? And the 8 1/2" would be a 215.9 mm lens?
    Yes, that's right.

    Quote Originally Posted by fralexis View Post
    According to the scale, the 14" scale shows a maximum aperture of 4.8 and the 8 1/2" lens has a maximum aperture of 10. Does this sound like I am understanding this?
    You have it backwards; the 8 1/2 inch configuration has a maximum aperture of f/4.8, and the 14 inch is a maximum of f/10.
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

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