Multiple - Fragmented Exposures

Discussion in 'Talk About Techniques' started by Ian Grant, Jan 17, 2018.

  1. Ian Grant

    Ian Grant Active Member Registered User

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    Each individual exposure is a significant underexposure, that underexposure increases with the number of exposures. So the individual exposures have insufficient light energy to give the expected. Think of it another way we flash paper or film with a weak white light exposure to reduce paper/film contrast but the exposure chosen is insufficient to cause base fogging as there's not enough light energy to cross the thresh-hold between unexposed and exposed.

    So you'll have more reciprocity with shorter and more exposures (particularly less than 1 second). There's not really a specific rule as it'll vary film to film, number of exposures etc. There are charts somewhere for number of flash exposures or using a strobe, and it's very similar. 4 exposures give an extra half stop, 10-12 exposures I'd give a full stop extra

    I've never had an under-exposure issue when I've made fragmented exposure, I've not bracketed - never used more than 1 sheet of film each time I've used the technique.

    Ian
     
  2. David M

    David M Well-Known Member Registered User

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    I think the process works the other way round. Dividing a long exposure into fractions doesn't give the same effect as the single long one. We encounter this when making test strips for printing. John B seems to have given some extra exposure, but used judgement rather than calculation.
     
  3. Ian Grant

    Ian Grant Active Member Registered User

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    Part of the issue with test strips is the enlarger lamp isn't instantaneous in reaching full output, so if you use multiple exposure that's a major factor.

    Ian
     
  4. David M

    David M Well-Known Member Registered User

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    Yes indeed, I wasn't suggesting an exact parallel.
     
  5. PaulBJE

    PaulBJE New Member Registered User

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    Thanks Ian,
    That is very helpful. I am currently using Foma film so plenty of reciprocity failure. I am hoping to switch to Fuji Acros when supplies arrive from Japan in February ( Its on restricted supply even there). I never allowed for reciprocity failure when using it for medium format but exposures tended to be shorter. From what you say I may need to make an adjustment with Acros also.

    Paul
     
  6. Ian-Barber

    Ian-Barber Admin Staff Member Registered User

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    I am going to put my neck on the line here with this question as is shows my low level of mathematics.

    When in the field, is there a simple way to reach the number of exposures required for a given meter reading.

    Scenario:
    • Meter reading tells me that I need to expose for 1/8th of a second at my chosen Aperture/ISO
    • I want to use a shutter speed of 1/30th and multiple exposures
    What is the process to quickly arrive at the number of exposures required.
     
  7. Ian Grant

    Ian Grant Active Member Registered User

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    4 exposures of 1/30 is equivalent to 1/8 but needs about 50%, half a stop, extra exposure so you need 6x 1/30 to overcome the reciprocity.

    This is an other fragmented exposure

    [​IMG]

    Ian
     
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  8. Ian-Barber

    Ian-Barber Admin Staff Member Registered User

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    Did you work this out in your head or is there an easy way to do it with a calculator o_O
     
  9. Ian Grant

    Ian Grant Active Member Registered User

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    I can do it quickly on my head, it's s very simple x2 factor between each stop.

    Ian
     
  10. Ian-Barber

    Ian-Barber Admin Staff Member Registered User

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    I do like the ways its rendered the movement in trees
     
  11. Alan Clark

    Alan Clark Member Registered User

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    Ian (Barber,) There is a very easy way to do it in your head. Just count ONE, TWO, FOUR, EIGHT, SIXTEEN, and so on....So if the single exposure required is 1/8th, as in your example, just count ONE 1/8th, TWO 1/16th, FOUR 1/32nd, EIGHT 1/64th. etc. i.e. EIGHT exposures of 1/64th. In practice this would actually be EIGHT separate exposures of 1/60th.
    How do you calculate the extra exposures needed to counteract reciprocity failure? I don't know. I'm no mathematician, and suspect it may vary with the brand of film being used. But there is no need to beat yourself up over this. After all, instead of giving EIGHT separate exposures of 1/60th, suppose you gave TWELVE. If reciprocity failure didn't exist you would only have over-exposed by half a stop. This is hardly a hanging offence. You could probably double the EIGHT to SIXTEEN and still get away without being arrested.

    Alan
     
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  12. andrewbartram66

    andrewbartram66 New Member Registered User

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    Hello

    Never poster to this site - will go back and do intro shortly.
    This post and thread was really interesting as I too had the pleasure of meeting John at an Inside The Outside weekend print workshop in Nottingham a year or two back. He have a talk about tonality and zone rulers then showed us some prints to illustrate the points he was discussing. The second day was spend critiquing our negs and making prints from them in the darkroom.

    Getting to the point, his studies of energy in nature by fragmenting exposure lead to beautiful results and quite a bit different from a single time exposure, the water didn’t blur to cotton wool but retained a sense of “water” if you know what I mean but movement as well, you really have to see his prints.

    I’ve also been looking at Harry Callaghan’s steer photography where he uses a similar technique I think.

    Lots of fun lies ahead with my Toyo !




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  13. martin-f5

    martin-f5 Active Member Registered User

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    just a reminder, there's another workshop with John in Nottingham, May 19th this year....
     
  14. andrewbartram66

    andrewbartram66 New Member Registered User

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    Hi John

    Yes I saw that

    Just found a reasonably priced hardback copy of his printing workshop book as well

    He really is a lovely and inspiring gent

    Andrew


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