B&W copy negative from color (C-41)

[gmikol]

Hi--

I've come across mention a couple of times about being able to use a regular panchromatic film, like TMX to make an interpositive, and then a copy negative from a C-41 negative.

But as I think about this, one thing bothers me. Wouldn't the orange mask of the C-41 negative have the same effect as exposing through an orange filter? In principle, you could use regular color filters to adjust tonal balance (Red 25, Green 11, Yellow 8, etc.) but how would you "neutralize" the orange mask, though. It doesn't seem like just using filter would have the same effect as if the scene was shot originally on B&W with that filter.

Am I missing something?

--Greg

 

[Konical]

Good Morning, Gmikol,

Start out by copying the color negative without any filter. You'll probably get a B & W positive which will be OK once you get your exposure dead on. Then you're left with repeating the process to get a B & W negative.

Since you'll need to establish your basic exposure for a given set-up anyway, why not just plan on shooting an entire 35mm roll. That will give you the opportunity to do some bracketed exposures. With 36 exposures, you'll also have plenty of shots left for experimenting with different filters if you so wish.

Remember that making positives from negatives may require a different developing time, probably a little longer than "normal" to step up the contrast a bit. A lot will also depend on the density, contrast and color content of the negative being copied. Some experimenting will probably be necessary, both in the exposure and the processing steps. Once you have a basic idea about exposure and processing with the 35mm film, you can easily transfer the information you've gained to using 120 or sheet film, either of which will give higher-quality final results. A 35mm color negative copied to a 35mm B & W interpositive to a B & W negative to make a B & W print may give some strange-looking and possibly disappointing results, even if your procedure is flawless.

The same basic idea can be used by putting the color negative in your enlarger and exposing onto sheet film, using stepped exposures to establish correct time/f-stop.

Konical

 

[gmikol]

Thanks for the overview on copy negatives, Konical, but I'm generally familiar with the procedure. What I'm looking for is input from anyone who's actually made an interpositive/copy negative from a C-41 original.

1) Does the orange base of the C-41 negative affect the tonal balance of the B&W interpositive?
2) Is there a way to compensate ("neutralize") the orange mask (cyan or blue filtration?).
3) If I plan on going down this route, would a maskless C-41 like Rollei Digibase CN200 be a better choice?

Thanks--

Greg

 

[Konical]

Good Evening, Greg,

I actually have done it, but it's been a loooong time ago; generally, my goal at the time was simply decent-quality projectable 35mm transparencies. My possibly-faulty memory is that just shooting the copy positive without any filter seemed to work fine with pan film (I used the old Kodak High Contrast Copy film and processed either in D-19 or Dektol 1:1). I'd start with no-filter copying. Once basic exposure and processing techniques are established, filtration can always be tried if necessary, since you'll at least have a good starting point.

Konical

 

[keithwms]

I think you don't need to neutralize the mask. Several of us have successfully printed kodak bw400cn (which has a mask) to ordinary paper. And tmax is far more panchromatic than paper. So... it should work just fine. If the contrast of the interpositive is reduced a bit, that may be beneficial.

 

[Mike Wilde]

Howard Bond had a tutorial on making unsharp masks using tmax in Photo Techniques a few years ago. The work up allowed the unsharp mask density to be claculated and it should work fine.

I am working on learing the ins and outs of duping slides ( a work the mind excercise to understand colour better, along with an expired 100' of dupe film for $5 to help it along). If you are concerned, you could filter the mask back to neutral grey.

I have old RA-4 paper that prints b&w. I have used it to print colour negs to b&w; you can filter to manipuate red to change its contrast range to some degree.

I have also printed traditional b&w negs to print to b&w via ra-4 procesing of this paper ( 12" x250' for $20; I could not say no. ) I have used blank film leader for the orange mask the paper expects to see as a part of its default mask, or have just dialled in lots of Y and M in the right amount to balance what the analyser saw the mask as to clone the colour when I did not have a blank 4x5 c-41 neg and all looked alright.

So if you are worried about making a b&w interneg and then printing from some generation of the monochome interneg, yes, you can vary it's contrst and colur snsitivity of the subject (the c-41 film) just like you can filter a conventional subject to change how the b&w film sees contrast as it lays down its translation of the world to b&w.

I would look to the spectral sensitivity of the film, the characteristic film modulation function of the c-41 film, and the image characteristics of the image originally captured by the colur film and ome time to think about how they intersect to attack the issue techinically and scientifically.