Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 73,657   Posts: 1,623,768   Online: 1145
      
Page 1 of 3 123 LastLast
Results 1 to 10 of 23
  1. #1

    Join Date
    Jun 2005
    Location
    Troutdale, OR
    Shooter
    Medium Format
    Posts
    167

    Adjusting Exposure Times With Print Size

    I recall reading a while ago a formula for adjusting print exposure time as the enlargement size changes. But, I cannot recall where I read this. I assume that with an f-stop timer it's relatively simple to make these adjustments.

    My reason for asking is that I have several negatives I'd like to print on 5x7", 8x10" and 11x14" paper to test my theory that different images look best at one size; at least, they look better than when larger or smaller. It would be nice to quickly adjust the exposure time (or lens aperture) and make a series of three prints while the negative is still in the enlarger.

    Rich

  2. #2

    Join Date
    Jan 2006
    Location
    Oklahoma
    Shooter
    Multi Format
    Posts
    588
    Square your lens to paper distance for the first print size.
    Square your lens to paper distance for the new enlarged print size.
    Divide the second result by the first result.
    Take the first good exposure time and multiply it by this result to arrive at your new exposure time.

    Example:

    10"x10"=100
    15"x15"=225
    225/100= 2.25
    If the first exposure time was 11 seconds then multiply it by 2.25 for the enlargement. ie; 24.75 sec.

    My interpretation from "You and Your Prints", by William Hawken ISBN 0-8174-2114-9

    I have used this method many times with good results.
    Last edited by DannL; 11-08-2007 at 12:33 AM. Click to view previous post history.
    "Lo único de lo que el mundo no se cansará nunca es de exageración." Salvador Dalí

  3. #3

    Join Date
    Oct 2004
    Shooter
    Multi Format
    Posts
    726
    It's the same inverse square law used in flash calculations: to double the lens to paper distance you need four times the time. In practice, though, I find that it's easier to re-meter or do a new test strip when you enlarge more (or less).

    David.

  4. #4
    clogz's Avatar
    Join Date
    Dec 2002
    Location
    Rotterdam, The Netherlands
    Shooter
    Multi Format
    Posts
    2,838
    Images
    114
    You might also find that when enlarging you need a slightly harder grade of paper.

    Hans
    Digital is best taken with a grain of silver.

  5. #5
    matti's Avatar
    Join Date
    Jun 2005
    Location
    Stockholm, Sweden
    Shooter
    Multi Format
    Posts
    652
    Images
    13
    Or you can look at this diagram.
    by Ralph W. Lambrecht. From his book Way Beyond Monochrome, I think. It should be easy to use if you have a scale on your enlarger.
    I mostly use a table in Tim Rudmans "Master printer"-book. I often use it to first make test prints and moving up for the finals.

    /matti
    Last edited by matti; 11-08-2007 at 04:28 AM. Click to view previous post history. Reason: missed the url...

  6. #6

    Join Date
    Sep 2002
    Location
    Willamette Valley, Oregon
    Shooter
    Medium Format
    Posts
    3,684
    Quote Originally Posted by Sirius Glass View Post
    Twice the linear dimension on one side means four
    times the exposure [2 stops more] because you are
    dealing with area and not the length of one side. Steve
    The working focal length of the lens must be taken into
    account. As the lens is focused for larger prints it's focal
    length is lessened and the lens approaches it's rated speed.
    The lens becomes faster. The reverse holds true when
    increasing the working focal length.

    An Ilford EM-10 enlarging meter works well and is just
    the thing for what the OP has in mind. Works also as
    a ballpark densitometer if calibrated. Under $30. Dan

  7. #7

    Join Date
    Aug 2006
    Location
    London, UK
    Shooter
    Medium Format
    Posts
    457
    Hello
    Another variation of the inverse square law, similar to DannL's is the attached formula. It's easier than my scribble looks. The new length (L2) is divided by the old length. (L1) This figure is then squared and this is the factor to multiply your old exposure (T1) to find out the new one.(T2) In this example, a 5x4 print at 15 second exposure is calculated to 60 at 10x8. That's an easy one as if the paper is four times as big, it will obviously need four times as much light. Bit more usefull if it's something like 17.6 seconds. The formula has certainley helped when I suddenly realise I've only got a few sheets of 20x24 paper left to make one print as you can get a small print correct, then go straight for a big one, though as clogz points out a slight increase in contrast may be neccesary.
    Cheers
    Mike
    Attached Thumbnails Attached Thumbnails a-formula.jpg  

  8. #8

    Join Date
    Jun 2005
    Location
    Troutdale, OR
    Shooter
    Medium Format
    Posts
    167
    Thank you all for validating what seemed reasonable to me. Also, the pointers to Ralph's and Tim's books reminded me where I read about this.

    I do have Nick Linden's exposure meter so I can run some tests to calibrate the adjustment to my equipment, lenses, and paper.

    Much appreciated,

    Rich

  9. #9

    Join Date
    May 2005
    Location
    Daventry, Northamptonshire, England
    Shooter
    35mm
    Posts
    7,335
    There's also a small programme available at http://home.centurytel.net.dwilder57/timeAdjust.html where you put in the old and new dimensions and it works out the exposure time for you.

    pentaxuser

  10. #10

    Join Date
    May 2005
    Location
    Daventry, Northamptonshire, England
    Shooter
    35mm
    Posts
    7,335
    Sorry I have this bookmarked under Print Adjustments. I got it from an earlier thread where someone kindly directed posters to this site. I simply copied the address from the site but I have just tried it by clicking on the copied address and it said not found.

    I am not computer literate enough to know what to suggest now. Maybe it has simply disappeared

    pentaxuser

Page 1 of 3 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin