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Thread: Bellows Extension Factor and Reciprocity Failure for ULF???

  1. #1

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    Bellows Extension Factor and Reciprocity Failure for ULF???

    I have cobbled together a 20 x 24 with parts from Filip Harbart. I am using Ilford FP4 with an Apo Nikkor 1210 mm but I have not been getting consistent results because I have not worked out all the issues of BEF and RF. Things are looking underexposed.

    If I am getting an incident meter reading of 20, the meter says I need a half second at f128.

    If I have 6 feet of bellow (1829 mm) then my bellows extension factor should be:

    (1892 squared) / (1210 squared) = factor of 2.28. This is just a little more than one stop adjustment to the exposure. This would increase the exposure from half a second to just a little over 1 second.

    The FP4 film comes with a graph to adjust for long exposures. The graph seems to say that a “measured exposure” of 1 second should be adjusted to about 5 to 7 seconds. The graph is a little hard to ready – I am interpreting it.

    Any corrections to my calculations or advice about how I should be thinking about this? Thanks!! Francis Fullam, Chicago, Illinois

  2. #2
    Tracy Storer's Avatar
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    Re: Bellows Extension Factor and Reciprocity Failure for ULF???

    Your bellows extension adjustment looks correct, and although I have not used FP4 much, that looks like a good adjustment for reciprocity failure.
    If your negatives look thin, I suggest doing some testing at wider apertures, with near infinity subjects.....
    Your exposure and development may not be giving you "box" speed. I have always rated sheet film at lower than manufacturers ratings.
    Tracy Storer
    Mammoth Camera Company tm
    www.mammothcamera.com

  3. #3

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    Re: Bellows Extension Factor and Reciprocity Failure for ULF???

    a 1 sec exposure for fp4 calls for about 3 seconds
    google fp4 reciprocity and have a look
    use a sheet of 4x5 film taped in your holder if you aren't happy with blowing $$$$ per test.

  4. #4

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    Re: Bellows Extension Factor and Reciprocity Failure for ULF???

    I highly recommend the "reciprocity timer" app for apple iOS devices (iPhone/iPad/iTouch/etc) it's highly accurate and helps you take into account your bellows, reciprocity, filter correction, etc.

    I would recommend it to anyone having trouble with their calculations (even just as a "double check".

    Soon there will be a 3.0 version with "tweaks" to make the app more smooth to operate, but that's all aesthetic, functionally the current version works just fine.

    Click image for larger version. 

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  5. #5
    おせわに なります! Andrew O'Neill's Avatar
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    Re: Bellows Extension Factor and Reciprocity Failure for ULF???

    I have found manufacturer's data to be a bit over the top. For an indicated exposure of one second with FP4-Plus, I only give a third stop more exposure. This is from data I generated myself and have used in the field for many years.

  6. #6

    Re: Bellows Extension Factor and Reciprocity Failure for ULF???

    I agree your bellows correction looks good. I also feel that using an incident meter is a good choice. Remembering this chapter from the Beyond the Zone System (Phil Davis) manual you need to open up two stops.

  7. #7

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    Re: Bellows Extension Factor and Reciprocity Failure for ULF???

    One consideration nobody has mentioned is that you are using what is essentially an Artar design lens - the APO Nikkor is a process lens. The artar consists of 4 elements in 4 groups. That means there are four elements each with two air-glass surfaces. Approximately 3-4% of light intensity is lost in each air-glass surface. That is between 24-32% of the light which falls on the negative. Contrast is also lost. I ran into this issue when I started using a 12x20 camera and most of the lenses I used were red dot artars. I had to increase exposure and development time to compensate for the loss of both light and contrast compared to film shot with the Plasmats that I used on 4x5 and 8x10.

    Bob

    Quote Originally Posted by FrancisF View Post
    I have cobbled together a 20 x 24 with parts from Filip Harbart. I am using Ilford FP4 with an Apo Nikkor 1210 mm but I have not been getting consistent results because I have not worked out all the issues of BEF and RF. Things are looking underexposed.

    If I am getting an incident meter reading of 20, the meter says I need a half second at f128.

    If I have 6 feet of bellow (1829 mm) then my bellows extension factor should be:

    (1892 squared) / (1210 squared) = factor of 2.28. This is just a little more than one stop adjustment to the exposure. This would increase the exposure from half a second to just a little over 1 second.

    The FP4 film comes with a graph to adjust for long exposures. The graph seems to say that a “measured exposure” of 1 second should be adjusted to about 5 to 7 seconds. The graph is a little hard to ready – I am interpreting it.

    Any corrections to my calculations or advice about how I should be thinking about this? Thanks!! Francis Fullam, Chicago, Illinois

  8. #8

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    Re: Bellows Extension Factor and Reciprocity Failure for ULF???

    Quote Originally Posted by bobherbst View Post
    One consideration nobody has mentioned is that you are using what is essentially an Artar design lens - the APO Nikkor is a process lens. The artar consists of 4 elements in 4 groups. That means there are four elements each with two air-glass surfaces. Approximately 3-4% of light intensity is lost in each air-glass surface. That is between 24-32% of the light which falls on the negative. Contrast is also lost. I ran into this issue when I started using a 12x20 camera and most of the lenses I used were red dot artars. I had to increase exposure and development time to compensate for the loss of both light and contrast compared to film shot with the Plasmats that I used on 4x5 and 8x10.

    Bob
    Bob,

    That's why some people (mostly cinematographers but also photographers) use T/stops instead of f/stops.

    T/stop is the actual transition stop of the light per lens, the lens needs to be tested and marked.

    I don't know who would be able to do this but perhaps some research and you'll find someone.

    I've specialized by sticking to a particular lens design did 90% of my lens lineup so that I don't have this issue as badly.

    The other problem is that shutters aren't very exacting and so one lens might also not match another in shutter speeds.

    For ULF being B&W it's not really AS much an issue, but it is an issue.

    Once you learn your lenses, you can adjust knowing how they perform, but knowing the actual T/stops will save you a lot of testing.

  9. #9

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    Re: Bellows Extension Factor and Reciprocity Failure for ULF???

    Quote Originally Posted by bobherbst View Post
    One consideration nobody has mentioned is that you are using what is essentially an Artar design lens - the APO Nikkor is a process lens. The artar consists of 4 elements in 4 groups. That means there are four elements each with two air-glass surfaces. Approximately 3-4% of light intensity is lost in each air-glass surface. That is between 24-32% of the light which falls on the negative. Contrast is also lost. I ran into this issue when I started using a 12x20 camera and most of the lenses I used were red dot artars. I had to increase exposure and development time to compensate for the loss of both light and contrast compared to film shot with the Plasmats that I used on 4x5 and 8x10.

    Bob
    Bob, I came late to this discussion, sorry.

    Apo-Nikkors are single-coated. So are RD Apo Artars. Y'r estimate of the light they lose per air-glass interface is high.

    Single-coated surfaces lose ~ 1% per surface. See S F. Ray, Applied Photographic Optics, p. 74. 0.99^8 = 0.92, a negligible loss. 0.96^8 = 0.72, approximately in your ball park and a loss of only ~ half a stop. The gain from single-coating for lenses that aren't too complex (dagor, triplet, tessar, dialyte and plasmat types) is so small that for them going from single- to multi-coating doesn't improve transmission very much.

    The plasmats that you used on 4x5 and 8x10 have 4 four groups, i.e., have exactly as many air-glass interfaces as the process lenses you find low in transmission and contrast.

    I don't know why your dialytes don't perform as expected for you, but your explanation doesn't seem correct. Could they be hazy? Could internal reflections inside your camera be lowering contrast?

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