Couple of large format close up exposure questions

Discussion in 'Exposure Discussion' started by JeffD, Feb 12, 2006.

  1. JeffD

    JeffD Member

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    I am setting up some still lifes that will be about 1:1 very close up.

    When I meter the scene, should I meter from where the lens is, or where the film plane is? Normally, I wouldn't care, but shooting this close I am not sure.

    Also, is there some kind of calculator available online, that would let me punch in my lens focal length, what my bellows length is, and then tell me my additional exposure to add?

    Lastly, when measuring bellows length for something like this, would I measure from the diaphram opening of my shutter to the film plane, or the rear of the lens glass to film plane, or some other distance?

    Thanks for any comments.
     
  2. David H. Bebbington

    David H. Bebbington Inactive

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    Meter the subject normally (from where the lens is). Measure bellows extension from the lens diaphragm. For exposure correction, try this (from "The Manual Of Photography", pub. Focal Press):
     
    Last edited by a moderator: Jul 23, 2007
  3. Donald Miller

    Donald Miller Member

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    To answer your questions as you posed them:

    You would normally meter the object you are photographing.

    I don't know of an online calculator. I use the calculator in the Kodak Professional Photoguide I purchased over twenty years ago. I don't know if it is still available. If I want to do a quick and dirty calculation, I will take the focal length of the lens and convert to inches and the bellows extension in inches from the film plane to the lens and arrive at the corrected effective Fstop. In other words if I have a 210 mm lens (8 inch) and my bellows extension is 16 inches then the correct Fstop for exposure calculation will be F 16.

    When I check this in the Kodak Photoguide, it tells me a correction factor of 4 which is the same (2 stops). The magnification is 1 to 1.

    I measure from the film plane to the shutter. It serves the purposes.

    Good luck.
     
  4. vet173

    vet173 Member

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    I tried this when Donald mentioned it before, and it worked good enough fo transparencys.
     
  5. Dan Fromm

    Dan Fromm Member

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    You can do the arithmetic in your head. Magnification = (extension/focal length) - 1. I measure extension with a tape measure, from back of camera to diaphragm. Not quite correct, close enough. Exposure compensation, in stops, = magnification + 1.

    Stops run f/1, f/1.4, f/2, ... Everyone knows the sequence. Shutter speeds run 1, 1/2, 1/4, ... Everyone knows the sequence. Both sequences are engraved on the shutter and on the light meter. One stop compensation means, use next larger aperture (e.g., f/16, not f/22) or next slower shutter speed (e.g., 1/30, not 1/60).
     
  6. morkolv

    morkolv Member

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    For bellows extension I use the Quick-disc, its very fast, built-in focal length adjustments, and it Free!! See here QuickDisc
     
  7. Chazzy

    Chazzy Member

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    Just to be sure I understand the application of this, if I am exposing 4x5 film and the subject area is 8x10, I only need to increase the exposure by one stop?
     
  8. eddym

    eddym Member

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    Meter the scene with an incident meter at the subject.

    I carry a metric ruler and a pocket calculator in my camera case, and use them to calculate the exposure factor. I measure from the diaphragm of the lens to the film plane, divide that by the focal length, and square the result. The formula is: (LF/FL)squared. This will give you an exposure increase factor. For example, say you have a 180 mm lens, and your lens to film distance is 360mm. 360/180=2; 2 squared is 4. You need four times the exposure, or two stops. This saves you from having to calculate magnification.
    You can punch it in and get the answer faster than you can read this.
     
  9. JeffD

    JeffD Member

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    Thanks everyone for the answers! This helps me a lot, and will save me some incorrectly exposed film.

    Eddym: That calculation works for me- pretty simple to remember. How come you use an incident meter? Any particular reason?

    Morkolv: I tried the quick disk- the only problem is that it seems like I can never actually place the disc in my scene where I can "measure" it on the ground glass. For instance, currently I am doing a close up of a flower, which is in a vase. There is really no way to have the disc in the scene without an assistant holding it
     
  10. Bob F.

    Bob F. Member

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    I'm not exactly the world's most experienced but I have found that Blue-Tak is often my friend in these situations - or the disc can be popped in amongst the leaves etc. The beauty is that it does not have to be face-on to the camera: it can be at any angle; you just measure it along it's longest axis on the gg screen.

    Have fun, Bob.
     
  11. rbarker

    rbarker Member

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    As shown by the discussion so far, there are various ways to approach doing close-ups. In many cases, most perhaps, the exact magnification ratio is unimportant. You set up and compose as your eye suggests, allowing the magnification, and bellows extension, to fall where they may. Using either the Quick Disc (or, commercial equivalents) or the formula gives the exposure compensation needed.

    In other cases, you may want the magnification to be more precise - exactly 1:1, for example. In that case, you might start by setting the bellows extension at 2x the (real) focal length, and positioning the camera at 2x the focal length from the desired focus plane, adjusting lateral and vertical positioning to get the desired composition. In such a case, the 4x or 2-stop exposure adjustment is already set by the 2x bellows extension.

    In either case, I think it is best to meter by whatever method you've already proven to work for you - either reflective or incident. Then, make the exposure adjustments according to the selected method (disc or formula). By using your "standard" metering technique, you avoid introducing yet another variable into the process.

    What I've found handy when using the disc (I actually use the commercial version from Calumet), is to make a loop of (partially de-stickyfied) masking tape, so I can put that on the back of the target/disc and stick it to something in the scene (the primary focus point). Some care in placement is needed to ensure that it is square to the lens axis, of course.

    FWIW, the Rodenstock DOF calculator wheel (available from the usual retailers) also provides close-up exposure compensation info, and is handy to keep in the camera case. Mine sits in the same pouch as my small metric tape measure.
     
  12. rbarker

    rbarker Member

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    I don't think that is quite true, Bob. One axis of the target needs to be square to the lens axis, otherwise the measurement will be off.

    But, considering all of the other variables (e.g. shutter-speed accuracy), great precision isn't really required in most cases.
     
  13. Ole

    Ole Moderator Staff Member Moderator

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    That's why the QuickDisc is round. However you turn it, it's just as wide.
     
  14. argus

    argus Member

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    I also use the quickdisc for marco shots. Apart from the info on bellows extention, it is also perfect for focussing on the exact plane you choose to.

    If you got problems to place the quickdisc where you want to but find it physically impossible, use a desctop lamp with moving arm and stick the QD on it.

    G
     
  15. eddym

    eddym Member

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    Mostly because most of my closeup work with 4x5 is done in a studio with flash, so I use a Minolta Flashmeter III to take incident readings. It's dead accurate.
     
  16. Bob F.

    Bob F. Member

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    The Calumet closeup device is IIRC a square, so you would need to have one edge parallel, but the Quickdisc is, well, a disc, so is readable in any orientation.
    (http://www.salzgeber.at/disc/index.html) I printed it out and laminated it.

    Cheers, Bob.
     
  17. John Koehrer

    John Koehrer Subscriber

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    And you could use a third hand to hold the quick disc. They're available at hobby shops or Radio Snack. They're used to hold small items together for soldering.
    Small metal base w/2 alligator clips.
     
  18. rbarker

    rbarker Member

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    A QuickSphere would be obvious, but a tilted and turned disc can be easily misleading.
     
  19. vet173

    vet173 Member

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    I have a toothpick that I used with my quickdisc. I put the tip of one end in the disc then I can put the toothpick in the shrubs when I shoot flowers. I direct you again to Donalds method, after using it I threw away the disc as it's so much easier.