Why doesn't black and white direct positive paper require a reversal process?

[pkr1979]

Hi all,

How can direct positive black and white paper be developed as regular paper and still make positives?

Cheers
Peter

 

[koraks]

You may find this post useful: https://www.photrio.com/forum/threads/how-does-direct-positive-film-work.15239/post-211857
This goes a little deeper: https://www.photrio.com/forum/threads/direct-positive-paper-how-does-it-work.68539/
In both cases, if you just read @Photo Engineer's posts, you get the gist of it.

 

[pkr1979]

Thanks!

Are the disadvantages described here the reason there is no direct positive black and white film: https://www.photrio.com/forum/threads/direct-positive-paper-how-does-it-work.68539/post-965322 ?

 

[koraks]

Thanks!

Are the disadvantages described here the reason there is no direct positive black and white film: https://www.photrio.com/forum/threads/direct-positive-paper-how-does-it-work.68539/post-965322 ?

The bit about tonal scale/latitude, I imagine, would have been relevant. Moreover, a key element in photography has always been the aspect of reproduction. A negative-negative process is inherently suited for that in an efficient way: you create an in-camera negative, and then make as many prints from that at whatever size you want with another negative-working process.

If you start with a film positive, you first have to turn that into a negative again to use a negatve-working printing process, or you'd also have to use a positive-working printing process. The latter would led you to a positive-positive process, which theoretically is feasible too, but then you'd hit upon the drawbacks outlined earlier.

 

[pkr1979]

The bit about tonal scale/latitude, I imagine, would have been relevant. Moreover, a key element in photography has always been the aspect of reproduction. A negative-negative process is inherently suited for that in an efficient way: you create an in-camera negative, and then make as many prints from that at whatever size you want with another negative-working process.

If you start with a film positive, you first have to turn that into a negative again to use a negatve-working printing process, or you'd also have to use a positive-working printing process. The latter would led you to a positive-positive process, which theoretically is feasible too, but then you'd hit upon the drawbacks outlined earlier.

Yep - but there could be room for just one direct bw positive film

 

[koraks]

Undoubtedly so. I also suspect that the market for this will be kind of small and I guess the manufacturers feel the complexity of the product and the R&D effort outweighs its market potential. Otherwise, it clearly would have existed!

 

[dpurdy]

I have a lot of B&W direct duplicating film in my freezer. It is how I make platinum prints from roll film. I have a bunch of it because it was discontinued and I wanted to continue using it. It goes negative to negative but would also go positive to positive. It is full tonal range and very development flexible contrast. I don't know how it works but Ithink it was somehow pre-exposed. It processes in standard metol/hydroquinone type developer.

 

[pkr1979]

I have a lot of B&W direct duplicating film in my freezer. It is how I make platinum prints from roll film. I have a bunch of it because it was discontinued and I wanted to continue using it. It goes negative to negative but would also go positive to positive. It is full tonal range and very development flexible contrast. I don't know how it works but Ithink it was somehow pre-exposed. It processes in standard metol/hydroquinone type developer.

What is this film called and who produced it?

 

[MattKing]

X-ray duplicating films were designed specifically for this sort of thing, and until recently were easily found and used extensively.
They were normally used in contact with large originals, and the way they are/were designed makes them challenging to use in camera.

 

[dpurdy]

What is this film called and who produced it?

Kodak direct duplicating film. I have it in 9.5 and 5 inch rolls. Kodak's recommended developer was D-19.

 

[MCB18]

Thanks!

Are the disadvantages described here the reason there is no direct positive black and white film: https://www.photrio.com/forum/threads/direct-positive-paper-how-does-it-work.68539/post-965322 ?

There is at least one direct positive film you can still get pretty cheap, Mikrat Ortho/FPP Super Positive. Unfortunately only available in 35mm. Would love to get some larger DP rolls for sheet films.

 

[pkr1979]

There is at least one direct positive film you can still get pretty cheap, Mikrat Ortho/FPP Super Positive. Unfortunately only available in 35mm. Would love to get some larger DP rolls for sheet films.

That is a prett slow film

 

[dokko]

I guess they are all slow, being designed for lab use, so fine grain was important and there's plenty of light.
maybe one reason that there is no variant for field use that it's difficult to increase film speed in this process?

found a tech sheet of one of the later Kodak versions (SO-132):

https://125px.com/docs/film/kodak/f11-Duplicating_SO-132.pdf

 

[nosmok]

I used (and will again) the Kodak SO-132 in the field, or at least in my backyard. Developing in Caffenol CL, my notes have the lower end of its speed range at around ASA 1/192, or about 24 seconds at f/5.6 in full sunlight (iirc I got OK results with 15 sec exposures, which is a little more practical). This is of course for long-expired film, if it was fresh it'd certainly be faster. But it really has a great look to it-- it's ortho (so reds go black) and grainless. I'll see if I can dig up a digitized shot. It's certainly usable for summer desert, mountain, or beach landscapes, and/or very sedentary people.