Bellows extension

Discussion in 'Large Format Cameras and Accessories' started by Terry Bowyer, Nov 2, 2008.

  1. Mainecoonmaniac

    Mainecoonmaniac Subscriber

    Messages:
    4,889
    Joined:
    Dec 10, 2009
    Shooter:
    Multi Format
    I used to shoot a lot of table top shots that required the calculation of bellows extension. I'm dyslexic and can't do math well. Calumet had this device that I used a lot. It was basically two pieces of plastic. One piece was a 2"x2" plastic square where I put in my shot. The other piece of plastic was a ruler about 1"x 4 inches long. I just measured the magnification of the square on the ruler and calculated the bellows extension. It was a simple and slick little device that was effective.

    Take a look at this link:

    http://www.cookseytalbottgallery.com/photo_blog_article.php?blRecordNumber=24
     
  2. holmburgers

    holmburgers Member

    Messages:
    4,481
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    I'm familiar with that, but it seems cumbersome, at least for "field" stuff. (as if taking a monorail into the field isn't cumbersome enough)

    My reasoning for wanting to have a table with subject distances is the ability to take some measurement-standard on your body. For instance, the "hang ten" sign with your hand; that distance won't change, and if you know what it is you could quite accurately measure distances in the field w/o a ruler or anything. The distance from your elbow to fingertips could be another measurement, and so on.

    Come to think of it, I'm just gonna get a huge ruler tattooed down the length of my arm and a yardstick down my leg.... :tongue:
     
  3. Greg Davis

    Greg Davis Subscriber

    Messages:
    2,158
    Joined:
    Feb 4, 2004
    Location:
    Nicholasvill
    Shooter:
    8x10 Format
    I don't understand why you want a complicated formula based on the subject distance when you could just velcro a measuring tape to your tripod and use your cell phone's calculator to figure the traditional bellows extension factor. It takes 30 seconds to get the right factor and then you can either divide the ISO by that factor to get a new ISO, or just have a table that gives the right aperture adjustment for each factor in third stops. You can even make it faster by printing a table of the square of each focal length you own so you can plug it in the calculator immediately without doing math.
     
  4. Ian C

    Ian C Member

    Messages:
    729
    Joined:
    Feb 8, 2009
    Shooter:
    Large Format
    Quick & Easy Bellows Compensation with a Calculator

    The easy way is to program a pocket calculator and take it with you. If you have trouble programming it there are many high school or college students who’d do it for you in a minute. You likely know at least one such person who’d do it for you.

    Once that’s done you carry a metric roll-up tape measure or a dressmaker’s tape (they have metric versions very cheap at any fabric shop). Here’s all you do.


    1. Compose and focus

    2. Measure the distance E from film plane to diaphragm in millimeters (this isn’t fussy)

    3. Enter f, E, and press the execution key to display the answer in f stops


    What could be simpler?


    The equation is

    x = 2*ln(E/f)/ln2

    where x = number of additional f stops for the bellows extension, E = bellows extension measured from the film plane to the diaphragm, and f = focal length of your lens.


    It isn’t rocket science and you really don’t need to know any math to use it.
     
  5. holmburgers

    holmburgers Member

    Messages:
    4,481
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    Thanks everyone, I know that you all have very good reasons for doing it the traditional way. It's simple and straightforward... I'll do it already!! However, I'm also wanting to take a fresh look at this and explore something different. Let's leave it at that. Besides, the more exposure mistakes I make, the more film I use and the more I'm feeding the market!

    I really believe that having an intuitive grasp of how subject distance relates to bellows factor would result in near instantaneous exposure compensations, in your head. It's much easier to estimate distances on the scale of feet and inches rather than mm or cm.

    Now, what was it that Robert Frost said?...
     
  6. Greg Davis

    Greg Davis Subscriber

    Messages:
    2,158
    Joined:
    Feb 4, 2004
    Location:
    Nicholasvill
    Shooter:
    8x10 Format
    If your subject is at twice the distance from the lens than the focal length of that lens, it is a factor of 4, or 2-stop difference (e.g. 300mm distance using a 150mm lens). If the subject is 3 times the distance from the lens than the focal length, it is a factor of 2, or 1-stop adjustment. If the subject is at an infinite distance from the lens, the factor is 1, or 0-stop difference.
     
  7. John Koehrer

    John Koehrer Subscriber

    Messages:
    7,237
    Joined:
    Apr 3, 2004
    Location:
    Aurora, Il
    Shooter:
    Multi Format
    IMO Greg's got the easiest solution and is more or less what I use.
    My method(?) goes like this:
    With a 150mm/6" lens,
    infinity=0,
    275mm/9"=1 stop,
    300mm/12"=2 stops.
    Halfway between gets half the correction 1/3 gets 1/3 the correction. Plus or minus depending which side you're measuring from.
    With my hand, 9" is the spread from thumb to little finger whilst hanging ten.
     
  8. RodKlukas

    RodKlukas Member

    Messages:
    21
    Joined:
    Oct 23, 2007
    Shooter:
    4x5 Format
    To all,
    Here is a simple way to calculate compensation requiring only an inch tape measure.
    take the focal length of your lens in inches and the extension of the bellows in inches and using these numbers change the unit to Fstops.
    What is the difference? that is the number of stops you must compensate.
    example a 210mm is approximately an 8" lens and with a 16" extension you derive f8 and f16. What is the difference between F8 and F16? 2 stops!
    You're done. BTW, wide angles are terrible for closeup due to excessive lateral chromatic aberration. Questions see RodKlukas.com
    Should help you all. 75mm= 3"= F2.8 1/3, 90mm = 3.5"=F3.5(2.8 2/3), 135mm = 5.6"=F5.6(close enough) etc
    Thanks,
    Rod
     
  9. Q.G.

    Q.G. Inactive

    Messages:
    5,554
    Joined:
    Jul 23, 2007
    Location:
    Netherlands
    Shooter:
    Medium Format
    Remember though that the extension in this methode is the full lens to film distance.

    I mention that, because when SLRs are involved it is normal practice to use only the extra extension (the length of an extension tube, or bellows put between lens and camera) in calculations.
    So when using the above method to calculate the compensation you need for an X" focal length lens with an Y" length tube, you have to add those X" to the length of the tube Y before 'converting' them into f-numbers.
     
  10. Q.G.

    Q.G. Inactive

    Messages:
    5,554
    Joined:
    Jul 23, 2007
    Location:
    Netherlands
    Shooter:
    Medium Format
    Your "275mm/9"=1 stop" is off target by as much as 0.75 stops (should be 1.75 stops).
    1 stop would be at 212 (and a bit) mm.
     
  11. steelneck

    steelneck Member

    Messages:
    173
    Joined:
    Nov 16, 2009
    Shooter:
    35mm
    I just had to see it again. Jason is really good at doing those videos, they are both fun and educative.
     
  12. cowanw

    cowanw Member

    Messages:
    1,520
    Joined:
    Aug 29, 2006
    Location:
    Hamilton, On
    Shooter:
    Large Format
    perhaps he meant 225mm
     
  13. hcm

    hcm Member

    Messages:
    3
    Joined:
    Apr 17, 2010
    Shooter:
    4x5 Format
    As the lens gets further from the film the light passing though the lens is spread over a wider area and proportionately less falls on any given area. The proportion is based on the square of the change in distance. Thus if the lens were twice as far away the light would be diffused over an area twice as high and twice as wide so the adjustment would be based on one quarter of the light hitting any area of film and the adjustment would be 2 f stops.
     
  14. Sponsored Ad
  15. stradibarrius

    stradibarrius Member

    Messages:
    1,454
    Joined:
    Jan 17, 2009
    Location:
    Monroe, GA
    Shooter:
    Medium Format
    I .tried measuring my bellows extension for this shot the bellows from the film plane to the lensboard is 16". My lens is 180mm. If I square the extension and divid by the square of my lens length I come up with 5 stop bellows factor??? Is this right?
    Obviously this is a very close up shot. This is the total extension of the bellows.
     
  16. johnielvis

    johnielvis Member

    Messages:
    973
    Joined:
    May 21, 2010
    Shooter:
    Medium Format
    16" extension / 180mm lens

    that's the bellows FACTOR...not the stops--

    FACTOR is used to multiply exposure TIME...

    you want STOPS, what you really want is to know how many doublings it takes to get to that number

    so if you get 5 for the FACTOR, you want to solve

    2^n = 5 (where n=the Number of stops)

    take logarithm of both sides: n*log2 = log5--this gives n = log5/log2 = 2.3

    so you need 2 and one third stops compensation for this setup
     
  17. rmolson

    rmolson Member

    Messages:
    330
    Joined:
    Feb 23, 2006
    Location:
    Mansfield Oh
    Shooter:
    Medium Format
    The Kodak Master Photoguide has a very comprehensive f number computer and simple way of determining exposure correction I have one taped to the back of my view camera glass cover.That and a pocket tape measure and you can figure the correction in seconds with out all the math. If I have a 6 inch lens 8 inches from the film plane my exposure should be increased by one stop.
     
  18. Bruce Osgood

    Bruce Osgood Membership Council Council

    Messages:
    2,635
    Joined:
    Sep 9, 2002
    Location:
    Brooklyn, N.Y.
    Shooter:
    Multi Format
    Strad,

    I did the math and keep a copy in my bag


    FILTER FACTOR & STOPS

    FACTOR.. ..STOPS
    1 0.0
    1.5 0.6
    2 1.0
    2.5 1.3
    3 1.6
    3.5 1.8
    4 2.0
    4.5 2.2
    5 2.3
    5.5 2.5
    6 2.6
    6.5 2.7
    7 2.8
    7.5 2.9
    8 3.0
    8.5 3.1
    9 3.2
     
  19. Bruce Osgood

    Bruce Osgood Membership Council Council

    Messages:
    2,635
    Joined:
    Sep 9, 2002
    Location:
    Brooklyn, N.Y.
    Shooter:
    Multi Format
    OOP'S

    the format did not hold up.

    The FACTOR should read as a number and decimal point, IE: factor of 1 is 1.0, 1-1/2 is 1.5.
    The STOP numbers are one decimal point also, IE: STOP of 1 is 0, STOP of 1.5 is 0.6

    Sorry the column spacing between the numbers didn't work.
     
  20. johnielvis

    johnielvis Member

    Messages:
    973
    Joined:
    May 21, 2010
    Shooter:
    Medium Format
    well....that's basically a table of logaritms base 2....I prefer to just do something I call the "effective f stop"

    you measure the lens extension then you divide by the lens focal length (the infinity "marked" focal length)

    this give you a multiplier for the fstops on the lens...for instance if you have an extension of 140mm and the lens is 100mm then your muliplier is 1.4...so f5.6 as marked on the lens is now an "effective fstop" of 5.6*1.4 = 8

    so I call it "f8 effective" when the lens is set at f5.6 at that bellows extension....
     
  21. Bruce Osgood

    Bruce Osgood Membership Council Council

    Messages:
    2,635
    Joined:
    Sep 9, 2002
    Location:
    Brooklyn, N.Y.
    Shooter:
    Multi Format
    John, I agree.

    I made the all to common mistake of answering the wrong question.

    I was addressing filter factors and not bellows extension.
     
  22. RalphLambrecht

    RalphLambrecht Subscriber

    Messages:
    10,213
    Joined:
    Sep 19, 2003
    Location:
    K,Germany
    Shooter:
    Medium Format
    try thisand start on pge 192!
     
  23. artonpaper

    artonpaper Subscriber

    Messages:
    337
    Joined:
    Aug 7, 2007
    Location:
    Staten Island, New York
    Shooter:
    Multi Format
    My method is to measure the bellows extension, from the ground glass to the lens board, which, believe me is close enough, then divide that number by the focal length of the lens, square that number, which yields your Bellows Extension Factor, BEF, then divide your ISO by your BEF and set that into the meter and take your reading. Being super precise is not usually necessary, although when shooting chromes it can't hurt.

    Example: 11 inch bellows extension, 8 inch lens, = 1.375 X 1.375 = 1.89. ISO 100 divided by 1.89 = 52.9, for a working exposure index (EI) of 50, which in this case will yield a one stop correction. All of this will keep you in a 1/3 f-stop tolerance, an industry standard.
     
  24. artonpaper

    artonpaper Subscriber

    Messages:
    337
    Joined:
    Aug 7, 2007
    Location:
    Staten Island, New York
    Shooter:
    Multi Format
  25. PanaDP

    PanaDP Member

    Messages:
    79
    Joined:
    Sep 9, 2008
    Shooter:
    8x10 Format
    I know this has been well and thoroughly covered but perhaps the way I prefer to do it will be of use to somebody. I don't really care for doing math in the field. I want everything prepared for me. I just sit down at my computer and fogure out the bellows extensions for a given focal length that will evenly correspond to stop corrections in 1/3 stop increments going out as far as the bellows on my camera will allow. I then make a small table with P-Touch tape and stick it to the lensboard for that lens. That ensures that I can simply set up the photograph I want and then choose the closest stop correction from the table.

    Here's how the tables look, this one is for a 90mm:

    90mm

    +1/3 - 106mm (4 3/16")

    +2/3 - 121mm (4 3/4")

    +1 - 127mm (5")

    +1 1/3 - 142mm (5 9/16")

    +1 2/3 - 156mm (6 1/8")

    +2 - 180mm (7 1/16")

    +2 1/3 - 202mm (7 15/16")

    +2 2/3 - 226mm (8 7/8")

    +3 - 255mm (10")

    +3 1/3 - 285mm (11 1/4")

    +3 2/3 - 321mm (12 5/8")

    +4 - 360mm (14 3/16")

    +4 1/3 - 404mm (15 15/16")

    +4 2/3 - 454mm (17 7/8")
     
  26. Larry L

    Larry L Member

    Messages:
    36
    Joined:
    Oct 19, 2005
    Location:
    Iowa
    Shooter:
    35mm RF
    I use Kodak photoguides for all my lens extension calculations since they have a dial system in the back of the books that will provide the exposure correction by you indicating what focal length of lens is being used along with how much extension you are experiencing. No math (calculator, etc.) is required. Both the Kodak Pocket Photoguide and the Kodak Professional Photoguide have this. The latter also has an extensive section on view camera perspective and depth-of-field controls as well as guides on camera movements. These can be found on E-Bay for reasonable prices as I'm sure they're out of print.
     
,