Bellows factor conversion method????

Discussion in 'Large Format Cameras and Accessories' started by stradibarrius, Feb 20, 2011.

  1. stradibarrius

    stradibarrius Member

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    I just found this Bellows Factor Conversion method.

    lens focal length of 210mm and a bellows draw of 450mm. Pretend these numbers are f-stops...drop the zeroes and you have 21 and 45.

    How many stops between 21 (f22) and 45 (f45)... Right, the bellows factor is 2 stops. Increase your exposure by 2 stops.

    If this is a valid method it is really simple. What do you experienced folks think?
     
  2. Christopher Walrath

    Christopher Walrath Member

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    I would say it is not only valid but simple. A no brainer for someone with basic math skills and a knowledge of a standard-ish aperture series. Cool beans.
     
  3. stradibarrius

    stradibarrius Member

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    This method is is amost identical to Paul_c5x4 method. He converts to inchs and the length becomes the f/stops and your bellows factor is the difference in f/stops.
    I am trying to do a real close up shot right now with my bellows fully extended 16" (409mm) and a 180 mm lens. So 410 become f/41 and 180 becomes f/18.. The difference is 2 1/3 stops????
    Is that correct?
    I also have made a copy of the "Quickdisc" but in this particular example the disc is slightly larger than the 2 stop measuring scale.
     
  4. Vaughn

    Vaughn Subscriber

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    My method:

    "The bellows are way out there...I'd better double the exposure! And maybe I'll take another shot and double it again." :D
     
  5. paul_c5x4

    paul_c5x4 Subscriber

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    Not my method - I found it mentioned over on one of the large format forums. I don't think it makes any difference if you work in inches or millimetres, just stick with what ever you are comfortable with.
     
  6. silveror0

    silveror0 Member

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    2-1/3 stops is correct. If you're using a filter also, then you need to ADD the filter's correction (in stops) to that. If your resulting exposure time exceeds one second, you may need to also consider reciprocity.
     
  7. MurrayMinchin

    MurrayMinchin Membership Council Council

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    I sat down with a calculator and marked off the factors for each of my lenses on a ruler. Now it's a complete no-brainer...just hold one end of the ruler at the film plane and apply the factor that's adjacent to middle of the lens. For a morning of mathematical pain I now have a lifetime of convenience.

    Murray
     
  8. 2F/2F

    2F/2F Member

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    You should end up with a bellows factor of about 4.6 for that situation, and using the method, you end up with a bellows factor of 4. A fraction (about 1/6, or 1/2 of 1/3) of a stop of underexposure might not be noticed, but if you are shooting transparencies, I would just do the math, which is very simple...and since it is very simple, why not just do it for all types of film? Just carry a pocket calculator. Divide the smaller number into the bigger number. Then square the product. There is your factor. Multiply that by your exposure time to get the new exposure time at the same f stop. Since you are on a tripod and likely (hopefully, if you are actually thinking about what you are doing) have a set amount of depth of field in mind for the shot, shutter speed is the more sensible and easily fluid exposure parameter to change in most situations. However, if you would rather change f stops, you can just use it as you would use a filter factor. You can easily enough remember the commonly used filter factors, or carry a chart with you.

    If this is something you do a lot, definitely do what Murray does. I use a tailor's tape, not a ruler, but that is not important.
     
  9. mike c

    mike c Subscriber

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    Rob,the small number is focal length of lens focused on infinity,and the large number is a focus closer than infinity?

    Mike
     
  10. 2F/2F

    2F/2F Member

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    Hi, Mike.

    That's right. The smaller number is the FL of the lens at infinity. The large number will be the extended distance measured from the film plane to the same point on the lens that corresponded to the FL when the lens was focused at infinity. This will usually be at the plane of the aperture.

    (450/210)² = easy

    With telephoto lenses, you are better off using magnification as a guide by using an object of a known size (such as a ruler) in the shot and measuring it on the ground glass, then using those two numbers to do the math.
     
    Last edited by a moderator: Feb 20, 2011
  11. TareqPhoto

    TareqPhoto Member

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    Buy that DoF calculator.

    Good luck!
     
  12. mike c

    mike c Subscriber

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    Thanks Rod,easy sounds good,I can under stand where a telephoto lens would cause some problems with its shorter than rated focal length.Gotta get me one of those calculators.

    Mike
     
  13. ic-racer

    ic-racer Member

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    Works for me.

    If I am looking for a more exact measure, then, in order of preference, I'd use a TTL meter, followed by an image height scale. The probelm I have with measuring exact bellows extension is uncertainty as to the location of the lens nodal point and exact focal length of the lens.
     
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  15. RalphLambrecht

    RalphLambrecht Subscriber

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  16. stradibarrius

    stradibarrius Member

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    Ralph when I print this calculator how long should the scale ruler be and what are the dimensions of the target? I want to verify that my printer did not change the scale.

    Is this calculator in "Way Beyond MonoChrome"? I got a copy last week and have only skimmed it so far.
     
  17. RalphLambrecht

    RalphLambrecht Subscriber

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    Print it full scale. Whatever inaccuracy your printer might have will be insignificant. Page 192 and 520.
     
  18. Rick A

    Rick A Subscriber

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    Ralph, I made two of your calculators and laminated them. One lives in my LF gear bag, my daughter grabbed the other. This is the handiest no brainer accessories I own. Thank you.
     
  19. Peter Schrager

    Peter Schrager Subscriber

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    Fred Picker had a method of bellows factor that was fast and simple. If we have and 8 inch lens and we increase the bellows to 10 inches then I just do a factor of 1 stop extra...you can fudge it a little but it works for me..just bring a measuring tape along in the field or wherever you go. no charts and no calculations...KISS PEOPLE!
    have a nice day!
    Peter
     
  20. 2F/2F

    2F/2F Member

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    10/8 = 1.25.
    1.25x1.25 = 1.56

    You and Mr. Picker favor 2/3 stop of overexposure as a matter of course? Your picture will live with negative film, yes. But it is not ideal. And it will make shots on transparency film (or digital, for that matter) end up obviously technically flawed.

    And how do you generalize that method for when people do not have an 8 inch lens at 10 inches of extension? You'd need to use percentages instead of just a single example. So, "extend bellows to 125 percent of focal length, and you add a stop." Except that is not correct. Not even really close.

    Sounds too complicated to me, besides that fact that it only works with negatives, and sloppily at that...

    Just divide the little number into the big number, then square the result. Simple.

    If you meant to write "12" where you wrote "10," you are correct. If you extend to 150 percent of the focal length, you add a stop. But the typo is just one example of what can happen in your brain when working on the shot. Easier to stick to the standard formula IMO.
     
    Last edited by a moderator: Feb 21, 2011
  21. onnect17

    onnect17 Member

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    If I remember correctly (from Steve Simmons book "Using the View Camera") the rule if shooting within 10 times the focal length "Add 1/2 stop for each 25% increase in bellows extension". It works just fine.
     
  22. RalphLambrecht

    RalphLambrecht Subscriber

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    Thanks.

    The ruler works best with large-format cameras but I have used it successfully with my Hasselblad. I need to take the hood off, but then, I can easily use the ruler to measure the target.
     
  23. anon12345

    anon12345 Member

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    Mr. Adams explains Lens Extension Factor (bellows factor) on pages 68 & 69 in his book "The Camera". If you decide to add this book to your library, then you may want to pick-up "The Negative" and "The Print" while you're at it, to make a set. These books can be purchased used and fairly inexpensively through sites like Barnes & Noble and/or eBay. IMO all three are must-haves for a photographer's bookshelf.
     
    Last edited by a moderator: Feb 22, 2011
  24. jeffreyg

    jeffreyg Subscriber

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    Ditto for the ruler. I sat down with a calculator one day and figured the factors backwards by 1/2 stops so I would know the amount of extension. I marked the factors for each of my lenses on a small retractable metal tape measure that I attached to the strap of my light meter. It's easy to measure from the lens to the film plane and immediately have the compensation in f/stops.

    http://www.jeffreyglasser.com/
     
  25. jimgalli

    jimgalli Subscriber

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    For those who don't want to carry a calculator or a slide rule into the field with them, the original poster's method is spot on. 2 stops.
     
  26. RalphLambrecht

    RalphLambrecht Subscriber

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    How about a 135 mm lens and a 180 mm draw? I think the ruler weighs 10 g, less than any calculator, but about as much as the piece of paper to remember the equation or any mysterious shortcut.