Does Negative + Negative = Postive?

[Ektagraphic]

Hi Guys- It seems to me that in theory I could take a negative and expose it to another sheet of negative film. Would this create a positive? I know it may not be a great image (or would it be?). Am I nuts??

Thanks,

Patrick

[David William White]

not nuts, done all the time

[Ektagraphic]

Don't the movies do something like this? I'd probably like to try it with 4X5...I guess it would be simple for me to try black and white but color neg would be really cool.

[tiberiustibz]

Paper is merely another negative. It's the same thing, but the film is much faster and takes much longer to develop. You can acquire litho film which processes in normal paper chemistry or you can reversal process negatives to achieve the same effect.

[Ektagraphic]

If people still want transparencies and E-6 disappears, is this a way they could get them?

[wy2l]

If people still want transparencies and E-6 disappears, is this a way they could get them?

www.dr5.com

[Ian Grant]

If people still want transparencies and E-6 disappears, is this a way they could get them?

It's always been a commercial option, particularly when volumes of prints were required.

Any Pro lab usually offers the service.

Ian

[Ektagraphic]

I have never seen it offered....I'll take a look around. What do they call it?

[Ian Grant]

Duping

It can be onto negative or positive stock.

Ian

[jnanian]

there is a film still being made ( i think photo warehouse in oxnard california is the last to carry it ) ... duplicating film.

this emulsion is SLOW like asa 1 or less, and need a flood light to expose, or a really long exposure under an enlarger or projected onto ....
it duplicates what is being projected onto it in a single step ...
meaning if you project / contact a negative it ends up a negative, or
if you project / contact a positive / chrome it ends up a positive.

there have been threads here ( and elsewhere ) about this stuff ...
kodak called it SO-132 professional duplicating film, i think PW just calls
it duplicating film.

[keithwms]

Well, it's true in principle but not really in practice. Each time you dupe, you put the tones through another tone curve and you necessarily discard some tonal information. There is no perfectly linear tone curve in neg materials (although you can get quite linear, you can never get a perfectly linear curve unless you resort to that technology that we do not discuss here). Also, there can be the other technical issue of base fog... you add a bit every time you dupe. You might think, well I can just "print through" it, but still it cuts into the tones when you 'flip' the neg.

Granted, in many cases, what I am saying really doesn't matter because the details in the highlights and shadows on the toe/knee aren't so vital to a particular shot... and of course you can compensate for these effects in various ways. E.g. when neg duping, people often use different films and developers at each stage, aiming to retain as much tonal info through the whole process as possible while still ending up with a printable neg. There are numerous recipes for this and plenty of room for exploration, e.g. SLIMT might be a great way to keep highlight detail in the original neg and give it a better chance of showing up in the interpositive.

But... based on the abovementioned technicality, I stick to my answer: no, an analogue neg of a neg isn't a positive in the same sense that an original slide is a positive. The neg/neg process will have put the scene's tones through two curves, and maybe a third if you then print the positive. There will be generational loss.

Of course, there is a long history of successfully duping negs, e.g. Weston. I dabble in this and it can work well. But it turns out that the interpos you typically want for that process is not much like a 'real' slide, that'd be too contrasty unless you really compensate in development (I say this because I also turn slides into negs from time to time). The dupe neg is still good because the extreme tones can be picked up by the neg material; neg materials have miraculous ability to record extreme tones if you develop for it. We have to remember that neg duping works so well because the final destination is paper... and there's a big difference between that and projecting an interpositive.

I should add that I have 'printed' negs to glass slides and then result can be something quite close to a projectable slide, with quite good Dmax and Dmin. It is possible to get pretty good b&w slides that way.

[Ektagraphic]

there is a film still being made ( i think photo warehouse in oxnard california is the last to carry it ) ... duplicating film.

this emulsion is SLOW like asa 1 or less, and need a flood light to expose, or a really long exposure under an enlarger or projected onto ....
it duplicates what is being projected onto it in a single step ...
meaning if you project / contact a negative it ends up a negative, or
if you project / contact a positive / chrome it ends up a positive.

there have been threads here ( and elsewhere ) about this stuff ...
kodak called it SO-132 professional duplicating film, i think PW just calls
it duplicating film.

I'll look into it. I am interested more in what will happen if I lay one exposed and processed Portra neg on top of another portra neg that is unexposed and expose the exposed neg onto the unexposed portra

[David William White]

Keep it emulsion to emulsion!