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pushing/pulling reversal b&w


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#1 chris hoag

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Posted 19 March 2009 - 01:10 AM

so i understand that pushing b&w neg. gives you more contrast and pulling it gives you less contrast but i think i once read that this is the opposite for reversal b&w- pushing lowers contrast and pulling increases contrast. is this true? what happens to grain when reversal b&w is pushed/pulled? what about minimum and maximum densities?

i also understand that b&w neg. has more latitude than b&w reversal. does this mean that neg. has a higher d max and lower d min meaning darker blacks and lighter whites and thus can fit a wider range of tones in between these more distant poles or does it just mean that the tones in neg. don't "fall off" towards the shoulder and toe of the curve as much as in reversal (having nothing to do with d-min/max)?

thanks,
chris
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#2 Simon Wyss

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Posted 21 March 2009 - 06:44 AM

Your first question will be answered no as long as we discuss alterations of first development. A true reversal film consists of two mixed preparations: a higher speed and commonly pachromatic sensitized and a low speed unsensitized one. The difference in speed may be of the factor 10 or more. Camera exposure will actually not affect the low speed (fine) grains.

Now you can follow every explanation. Push first development results in more contrast and more graininess, push second development which only blackens the residual low speed salts results in higher max density of the positive. Keep in mind that the negative out of first development has a medium gamma value, while the complement of the dissolved and washed-out negative will be a higher gamma picture.

The negative-positive procedure can offer more latitude due to the fact that the usable contrast range may be slid between two separate films. The reversal film, strictly spoken, has latitude Zero since processing can only follow the film manufacturer's recommendations plus laboratory experience to produce the best of it. There is just so much silver salt available from one blend emulsion. Exposure is given, so everything comes into form perforce.
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#3 Brian Pritchard

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Posted 24 March 2009 - 03:31 AM

The contrast of black and white reversal is determined by the first developer. Pushing and pulling will have the same result on contrast and grain as in black and white negative processing. The second developer is timed to completion which means as long as you give it sufficient time increased time has no effect.

Because black and white reversal is designed for direct projection, it has a normal contrast of around 1.50; negative has a contrast of around 0.6. Higher contrast means less latitude so reversal films, and that includes colour reversal, have less latitude.

Brian
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