Anyone Use FP4 And Owns A Densitometer

Ian-Barber

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I would like to test the accuracy of the densitometer built into the VueScan scanning software.

I have just measured the film rebate (FB+F) of a sheet of Ilford FP4 5x4 film and according to the software, the density of the rebate is 0.20 so would be interested to see just how accurate it is.
 

Alan9940

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Is this an FP-4+ negative developed in Pyrocat? That's the only example I currently have on-hand and it reads 0.12
 

Ian-Barber

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Is this an FP-4+ negative developed in Pyrocat? That's the only example I currently have on-hand and it reads 0.12
Thanks Alan, I will double check my Pyro negative with the scanner again but im sure it read 0.20 in which case its a little out
 

Alan9940

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Thanks Alan, I will double check my Pyro negative with the scanner again but im sure it read 0.20 in which case its a little out
Maybe, not. I don't know anything about using a scanner as a densitometer, but when reading any stained negative with a densitometer, unless you have a unit specifically designed for a stained negative, a blue filter is used to simulate normal response. Maybe someone with experience using a scanner in this way will chime in.

As I was typing this response, Keith posted and it seems that we're pretty close in agreement. Therefore, I'd say the number you're looking for is somewhere around 0.12 - 0.13.
 

David M

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Two things puzzle me about this thread. May I ask for enlightenment?
Firstly, you are all quoting the various developers you have used. Does this mean that the developer has an effect on the entirely unexposed and fully fixed margin of the film? Would it not be prudent to fix, in new fixer, a fresh and unexposed sheet. How can you be certain that the film holder is not permitting a very small bleed into the margin?
Secondly, why not get a calibrated step wedge and scan it in tandem with an entirely unexposed, fully fixed and washed sheet of film? If the recorded density doesn't correspond exactly to one step, then two layers of film can be stacked and the corresponding value halved. As step wedges seem to be calibrated in thirds of a stop, three layers of film would give discrimination of one-ninth or as near as dammit an order of magnitude.
This is curiosity on my part, but I do like to know how things work.
 

Alan9940

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David, the developer used has very little effect on the outcome when measuring for fb+f...basically. I guess there could be some minute differences in "fog" level, but I've personally never measured it. I suppose a staining developer might reveal a slight increase, since there is an overall stain component with these developers. IMO, as with most things photographic it's all close enough.

When measuring an unexposed, but processed area of film I use an entire frame or sheet and take readings from the central area.
 

David M

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That's what I had imagined. If stain did affect the margins, then presumably every photographer would have slightly different stains, due to local conditions, processing and preferences. That would mean that every photographer's margins would record different FB+F+S densities. All this assumes that everybody's densitometer is uniformly calibrated.
 
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