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  1. #11
    Mike Wilde's Avatar
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    the version I made from JBrunner's idea has a 1.5" square target. I don't recall if I did any scaling though.
    my real name, imagine that.

  2. #12
    RalphLambrecht's Avatar
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    Quote Originally Posted by silveror0 View Post
    ... f-stops cannot be multiplied. ...
    f/stops are added rather than multiplied.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  3. #13
    johnnywalker's Avatar
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    Quote Originally Posted by Sirius Glass View Post
    To find the distance from the infinity position:

    distance = (focal length in mm)* square root(f/stop change wanted) in mm
    distance = (focal length in mm)* square root(f/stop change wanted)/25.4 mm/inch in inches

    Example:

    distance = 135mm * square root (4 f stops) = 135mm * 2 = 270mm

    I used this to mark off changes in f/stops from 0.0 [infinity] to 4.0 in 0.5 increments.

    Steve
    But if you want a 1 stop change, you get 135mm, and that should be a 0 stop change. Or am I missing something?
    For a 135mm lens I calculate a 1 stop difference at 191mm, 2 stops at 234mm, and 3 stops at 270mm.
    Last edited by johnnywalker; 11-13-2010 at 06:29 PM. Click to view previous post history.
    If I had been present at the creation, I would have given some useful hints for the better arrangement of the Universe.
    Alfonso the Wise, 1221-1284

  4. #14
    Christopher Walrath's Avatar
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    Redundant
    Last edited by Christopher Walrath; 11-13-2010 at 06:47 PM. Click to view previous post history.
    Thank you.
    -CW

    "Wubba, wubba, wubba. Bing, bang, bong. Yuck, yuck, yuck and a fiddle-dee-dee." - The Yeti

  5. #15
    johnnywalker's Avatar
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    Unhelpful
    If I had been present at the creation, I would have given some useful hints for the better arrangement of the Universe.
    Alfonso the Wise, 1221-1284

  6. #16

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    Math makes my head hurt. I learned the algebra in the '60's at a photo school. I always had a headache. Then I found out about the f/stop/inches method that Steve Sherman describes. I've been pain free ever since.

    I keep half a dressmakers tape in my bags and studio roller cabinet, that lets me hit my exposures within a third of an f/stop. But even using the guesstimate in your head method it puts you in the half an f/stop range. Then you just go over for negs and under for trans.

  7. #17
    Toffle's Avatar
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    The only time Salzberger's "Quick Disk" has failed me is the time I left it in the middle of a frame... nicely focused and perfectly exposed.
    Tom, on Point Pelee, Canada

    Ansel Adams had the Zone System... I'm working on the points system. First I points it here, and then I points it there...

    http://tom-overton-images.weebly.com


  8. #18

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    I crunched the numbers backward to find length and marked a small retractable metal measuring tape accordingly for each lens (3) in a different color permanent ink. It is attached with a key ring to the strap of a spotmeter. Its a no-brainer -- just measure from the lensboard to the film plane and see which exposure factor is the closest .

    http://www.jeffreyglasser.com/

  9. #19
    RalphLambrecht's Avatar
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    Quote Originally Posted by Toffle View Post
    The only time Salzberger's "Quick Disk" has failed me is the time I left it in the middle of a frame... nicely focused and perfectly exposed.
    I agree. What can be easier than using a focusing target and measuring the exposure modification off the screen with a ruler. It may not work in all and every situations, but it works in most cases and does so without math.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

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