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Why overexpose films with PMK Pyro development?

Xícara

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Hi Forum,

I'm curious as to why films are routinely shot at lower EI values than the standard ISO rating when using PMK Pyro development. I imagine that it must have something to do with the effects of staining. Can anyone please give a simple technical explanation?

Thanks,
 
In my case, a result of personal ISO testing. Not all of my films are shot at half box speed.I shoot Ilford SFX 200 at iso 250. Fomapan 100 and 200 are shot one stop overexposed, TriX 320 at rated speed.
 
Xícara said:
Hi Forum,

I'm curious as to why films are routinely shot at lower EI values than the standard ISO rating when using PMK Pyro development.
Thanks,
Click to expand...

I don't think there is a direct link between PMK Pyro and film speed i.e. it isn't like Perceptol where the maker says and nearly everyone else agrees that it is a speed reducing developer best shot at half box speed. However as has been said many do shoot at less than box speed because that is what their testing with their camera, their meter and their developer tells them is the right speed

pentaxuser
 
the thinking is to reach deeply into the shadows... PMK for example has the tannin effect where the highlights harden as they develop... lone single light bulb in dark room you can see the filament.... therefore this allows you to expose and get the deep shadows and with devolopment highlights harden and set first , then your midtones an finally the silver that is defining your shadow.s
 

Thanks, getting more shadow detail makes sense. So the fact that the highlights "harden" first (stabilise?), then the mid-tones, then the shadows, means that overexposure increases the overall dynamic range?
 


The speed marked on a film's package is only valid in whatever developer the manufacturer tested it in. Different developers give different real film speeds. It depends on the film, too. Most films lose speed in PMK, but not all. Thisis not unique to PMK; other developers give different speeds with different films, too.
 

This is really what you need to know. With the self limiting development that PMK has, you are free to expose it to get as much detail in the shadows as you want without having to jerk around with zone system type development.
 
I've used several developers over the years and PMK doesn't test out any slower than others that I've tested (HC-110, D-76). FWIW I shoot 320TX and TMY at E.I. 250 with PMK, Just 1/3 and 2/3-stop slower respectively. Plus I err on the side of overexposure in my testing, so "true" speed is likely a smidgen faster.

Best,

Doremus
 
Xícara said:
Thanks, getting more shadow detail makes sense. So the fact that the highlights "harden" first (stabilise?), then the mid-tones, then the shadows, means that overexposure increases the overall dynamic range?
Click to expand...
That is what I have experience in thousands of runs of PMK yes..
 
Also consider metering techniques and desired results. I learned to set Tri-X at 200 for portraiture to avoid shadowy eye sockets, for example.
 
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