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  1. #11
    Sirius Glass's Avatar
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    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
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  2. #12
    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.

  3. #13
    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

  4. #14
    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

  5. #15
    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.
    CWalrath
    APUG BLIND PRINT EXCHANGE
    DE Darkroom

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

  6. #16
    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

  7. #17
    Sirius Glass's Avatar
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    Quote Originally Posted by johnnywalker View Post
    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.
    Yes the equation is off. I ended up downloading the spreadsheet. The spread sheet was locked. I opened my own spreadsheet. The format of the equations had changed. Finally got it working.

    I cannot get it to line up here, but here it is ...

    Enter Lens Focal Length 135

    Bellows Scale f/stop
    Extension Distance Change

    60 0 0
    65 0 0
    70 0 0
    75 0 0
    80 0 0
    85 0 0
    90 0 0
    95 0 0
    100 0 0
    105 0 0
    110 0 0
    115 0 0
    120 0 0
    125 0 0
    130 0 0
    135 0 0
    140 5 0
    145 10 0.25
    150 15 0.25
    155 20 0.5
    160 25 0.5
    165 30 0.5
    170 35 0.75
    175 40 0.75
    180 45 0.75
    185 50 1
    190 55 1
    195 60 1
    200 65 1.25
    205 70 1.25
    210 75 1.25
    215 80 1.25
    220 85 1.5
    225 90 1.5
    230 95 1.5
    235 100 1.5
    240 105 1.75
    245 110 1.75
    250 115 1.75
    255 120 1.75
    260 125 2
    265 130 2
    270 135 2
    275 140 2

    Steve
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  8. #18

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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.

  9. #19
    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


  10. #20

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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/

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