Multiple - Fragmented Exposures

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
 
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.
 
David M said:
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.
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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
 
Yes indeed, I wasn't suggesting an exact parallel.
 
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
 
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.
 
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

kinlet-deep03sm.jpg


Ian
 
Ian Grant said:
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.

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

Ian
 
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
 
Alan Clark said:
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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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 !




Sent from my iPhone using Tapatalk
 
just a reminder, there's another workshop with John in Nottingham, May 19th this year....
 
martin-f5 said:
just a reminder, there's another workshop with John in Nottingham, May 19th this year....
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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


Sent from my iPhone using Tapatalk
 
Ian Grant said:
This is a technique for portraying movement useful with trees, water, clouds etc, instead of a blur you get small incemental steps.

elderflowers.jpg


Essentially you need a filter to increase the exposure times this could be a Neutral Density filter, a Polariser, or any deep filter that increases the Exposure factor. I tend to use a Green filter as it also separates the greens when there's foliage/leaves etc.

The idea is to use a series of shorter exposures to build up to the desired exposure the only problem is the exposures are prone to reciprocity failure so the sum needs to be greater than the whole, I usually aim for about half a stop but the more individual exposures the greater the increase needed. This is similar to using multiple flash exposures.

So an example might be a 1 second exposure at f22 is needed, we could break that down into six at 1/8 and 3 at 1/4 that's a total of 1.5 seconds. You need a good rigid tripod and camera particularly if you're changing shutter speeds, and careful re-cocking of the shutter. A Prontor or similar press shutter would be ideal but I've had no issues with my Wista 45DX and Copal shuttered lenses. You can uses so many different combinations of speeds and numbers of exposure it's a technique with numerous possibilities. It's not one I use a lot but when I have it's always succeeded.

highley06sm.jpg


You can use a similar technique for still lives adding or subtracting components between the exposures, John Blakemore did this in his Chimerical Landscapes around 1990 published in Inscape, I'm lucky enough to have a print from this series.

Ian
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Mind confirming something for me? If I take a reading of the set and it says 1 second at f/32, do I add exposure slightly then chop that time up for every additional exposure taken? Also, at that time, I'd expect slight reciprocity failure so 1 second plus the increase (making exposure time 1.5" or 2") would actually be 6 seconds or something or other.
 
RiverMikaelWrinch said:
Mind confirming something for me? If I take a reading of the set and it says 1 second at f/32, do I add exposure slightly then chop that time up for every additional exposure taken? Also, at that time, I'd expect slight reciprocity failure so 1 second plus the increase (making exposure time 1.5" or 2") would actually be 6 seconds or something or other.
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I've never had an issue of reciprocity at 1 second @ f32 with Tmax100 or Delta 100. But when adding up multiple exposures I'd typically add approx 50% extra.

Welcome to the Forum BTW, some images were lost a few years ago in an upgrade, I've just added them back in the original post.

Ian
 
Ian Grant said:
I've never had an issue of reciprocity at 1 second @ f32 with Tmax100 or Delta 100. But when adding up multiple exposures I'd typically add approx 50% extra.

Welcome to the Forum BTW, some images were lost a few years ago in an upgrade, I've just added them back in the original post.

Ian
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Thanks for the welcome! I'm loving this forum already.
 
Much depends on the final effect you want to see. A bit of experimental bracketing might be needed.
If you recall John’s pictures of moving water, it was the multiple highlights in the images that made them extraordinary. The surrounding rocks were rendered more-or-less normally. Your ambitions may be different.
I believe he did add some extra exposure to counter the intermittency, but he was very relaxed about precise technical details.
 
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