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  1. #21

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    I don’t know the nodal distance of the 150/4 APO Rodagon N. However, I have the nodal distance of the 150/5.6A EL Nikkor (1.2mm). That would inflate the true negative-to-print distance by 1.2 mm compared to the calculated value for the EL Nikkor. The error is small enough that the calculation is still sufficiently accurate for a reasonable estimate.

    The nodal distance of the 150/4 APO Rodgon N is likely not greatly different than that of the 150/5.6A EL Nikkor.

    A greater potential calculation error is the true focal length of the lens. A good example of this is the 50/2.8N EL Nikkor. Nikon gives its true focal length as 52.0 mm—4% greater than marked. Some makers supply this information. Others simply state the nominal focal length only.

  2. #22

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    Good info, I am pretty much trying to decide on the amount of travel needed to go from roughly 24"x36" to 50"x70"-ish for all formats. I am likely going to be using an 80" length of 7-1/2" lawn track that is commonly used for model railroading purposes, it should keep that axis *roughly* aligned and the fine tuning will be done with adjustments on the carriage and the CB7 head it self. So it sounds like 80" of travel should indeed cover the range, room will need to be at last 10' feet deep in order to hit the largest size, not that I am aiming for those huge sizes any time soon.....I still don't know how the hell I would pull off huge prints other than a Clyde Butcher or Bob Carnie style long tray room, but I will worry about that later, 30"x40" at the biggest for now...


    This ought to be fun to make too, I am ordering a model 3b LED Modern Enlarging Lamp for the CB7 head this Spring, should work great for this purpose. It's a really slick setup, the b version is not listed yet but his video covers it here:

    http://www.youtube.com/watch?v=Ein89audefA
    Last edited by PKM-25; 02-22-2014 at 05:48 PM. Click to view previous post history.

  3. #23
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    Quote Originally Posted by PKM-25 View Post


    This ought to be fun to make too, I am ordering a model 3b LED Modern Enlarging Lamp for the CB7 head this Spring, should work great for this purpose. It's a really slick setup, the b version is not listed yet but his video covers it here:

    http://www.youtube.com/watch?v=Ein89audefA
    Dan:

    While you are at it, see if you can convince the light source manufacturer to:

    1) provide an Android App for it; and
    2) develop an f-stop timer App as well .
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  4. #24

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    How to determine max enlarging size for my setup?

    ..
    Last edited by Erik L; 02-22-2014 at 09:29 PM. Click to view previous post history.

  5. #25

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    Okay,

    I'm trying to write the Excel formula for the equation for magnification given above, which is:

    Magnification is

    m = [d + squareroot(d^2 – 4df)]/2f – 1

    d = negative-to-print distance

    f = focal length

    However, I don't seem to have it right for some reason, and I can't figure out what I've done wrong.

    Here's my Excel formula (with the above variables instead of cell coordinates):

    =((SQRT((d^2)-(4*d*f)))+d)/((2*f)-1)

    Any help from the Excel experts out there?

    TIA

    Doremus

  6. #26

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    Eliminate the outer pair of parentheses to the right of the division slash.

    We want to divide the quantity to the left of the slash by 2f, and then subtract 1.

    I think that Excel follows the standard order of operations for algebraic expressions so that we can eliminate extraneous parentheses (which makes the expression easier to read as well).

    It should look like the original formula.

    = (d + sqrt(d^2 – 4*d*f) ) / 2*f - 1

  7. #27

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    Used to do 35mm KB14 (asa 25) to 20x24 in the late '60's and early '70's when I had a lab available with a Navy grade Omega D series. If you want really big with limited grain the film and ASA options become seriously reduced. I believe some Dursts will roll over to Horizontal for long throws and really big images.

  8. #28

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    Quote Originally Posted by Ian C View Post
    Eliminate the outer pair of parentheses to the right of the division slash.

    We want to divide the quantity to the left of the slash by 2f, and then subtract 1.

    I think that Excel follows the standard order of operations for algebraic expressions so that we can eliminate extraneous parentheses (which makes the expression easier to read as well).

    It should look like the original formula.

    = (d + sqrt(d^2 – 4*d*f) ) / 2*f - 1
    Aahh... The problem is not my Excel formula, but rather my misunderstanding of the original!

    Got it now! Thanks a million Ian.

    ...and, for those who want the right Excel string:

    =(((SQRT((d^2)-(4*d*f)))+d)/(2*f))-1

    Just replace "d" with the cell you want to enter the distance in and "f" with the cell you want to enter the focal length in.

    Best,

    Doremus

  9. #29
    ROL
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    I imagine the OP to be happily enlarging away after some 2½ years. Don't forget when calculating maximum enlargement for the purposes of designing a table capable of handling said enlargements, to account for room to crop – unless you're one of those inflexible, full frame, crop Nazis.

  10. #30

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    Quote Originally Posted by MattKing View Post
    Dan:

    While you are at it, see if you can convince the light source manufacturer to:

    1) provide an Android App for it; and
    2) develop an f-stop timer App as well .
    If I am not mistaken, the B version should allow for the use of a separate timer.

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