What is/was the purpose of slide duplication on roll film?

Once upon a time -- It was common practice to drag-out the slide projector. The same applies to movie film. Color prints on paper were possible but expensive. There were many reasons to duplicate slides and movies. We photofinisher's had special devices to do this task. It was good business. However, making the duplicates look exactly like the original was impossible. Most times, the duplicate picked up contrast due to a loss of scale. It was a chore to set-up these machines and thus the cost was high.

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Kodak would make prints from slides. They were made on a special Kodachrome film with a white base. They were exposed in a special camera and developed in a Kodachrome processing machine. As time went by, a reversal color paper was available. The output was good. The cost was under a dollar a print for a 3 1/2 by 5 1/4 inch print.

Professionals made slide shows of cities and popular attractions and these were sold en mass at tourist shops. Also schools were a market for professionally made educational stuff. Look up slide strip shows, a special projector that accepted 35mm film un-cut.

Would duplicate the slide with let;'s say medium format film keep the contrast down?

When I had medium format slide shots printed, they would shoot them with 4x5 negative film and then print from that.

What about using negative duplicating film rather than chrome to "duplicate" the 35mm chromes? Does that reduce the contrast?

Slide copies were also sold commercially, for example of landmarks, scenery, museum exhibits etc.

Handy when you presented your slide shows at home of your vacations. You'd stick in one or two in between the ones you took and mention nothing about it. :)

Some color originals held up poorly under repeated projection, while others would fade on their own, even in the box. Duplication was a common practice- often the dupes (as in Kodachrome, which was superb in dark storage, but tended to suffer from repeated projection) would be projected with the original stored in the dark with temperature control. There were special films made for duplication (Ektachrome 5071, for example) since copying to the same film as the original often stepped up contrast and color (sometimes good, sometimes bad - in the days before digital, we did what we had to do).

Duplication with CC filters was the path to color correction for slides, and sometimes even severely mal-exposed images could be somewhat rescued.

also see

Photography by Erwin Voogt

Would duplicate the slide with let;'s say medium format film keep the contrast down?

 

When I had medium format slide shots printed, they would shoot them with 4x5 negative film and then print from that.

 

What about using negative duplicating film rather than chrome to "duplicate" the 35mm chromes? Does that reduce the contrast?

The typical slide film displays 256:1 tonal range (if properly exposed and processed), A copy slide has a compressed tonal range, about 1 f-stop less = 128:1. Copy side film helps as does inter-negative film. We often made a copy as a color negative on this film. Then we exposed this negative on special film, similar to motion picture release film. Cine films were often shot using a color negative film and then printed for theater release. Since the life of a theater print film was short, a theater would order several copies. .

I have been in the AV staging business for 40 years. From 1984 - 1996 I programmed multi image slideshows. These shows were often backed up for safety's sake. In recent years I have been collecting staging gear, and more recently have been given a cache of slide modules, which I have been capturing to video and putting on youtube. Regarding fading slides, I am seeing that a particular 15 projector show I have here, that includes an original and dupe set, look very different. The original is "all good" but the dupe set is badly faded, especially in the black areas of each slide. I have been told that Ektachrome 5071 was the duping stock of choice. I blame that! Here is a video that includes two copies of the show running in sync - the original, and the dupe set. See if you can guess which is which! All of these slides are 45 years old.

Dropbox - master_set_vs_dupe_set.mp4 - Simplify your life

Here is my youtube channel with 20 or more shows, from 3-15 projectors each:

https://www.youtube.com/channel/UCdGRNxsrsI-efMFSjFDmzvg/videos

Needless to say, I hope you subscribe to the channel - I have more of these to restore and capture!

Steve

www.stevenmichelsen.com/AVL

The typical slide film displays 256:1 tonal range (if properly exposed and processed), A copy slide has a compressed tonal range, about 1 f-stop less = 128:1. Copy side film helps as does inter-negative film. We often made a copy as a color negative on this film. Then we exposed this negative on special film, similar to motion picture release film. Cine films were often shot using a color negative film and then printed for theater release. Since the life of a theater print film was short, a theater would order several copies. .

How many generations from camera negative to release print for feature film movies?

And yet they keep them looking right all the way through.

The shop I was working at about 10 or so years ago had 1 customer that would request duplicate slides. He was using the duplicates to mail in as submissions for photo shows and contests.

I would assume most duplicates were made for preservation purposes.

The shop I was working at about 10 or so years ago had 1 customer that would request duplicate slides. He was using the duplicates to mail in as submissions for photo shows and contests.

 

I would assume most duplicates were made for preservation purposes.

Too bad that it appears that the dupe stock didn't hold up as well as the original film (in the AV production and staging world, Kodak 6017 (Ektachrome 64 Professional) was used for origination and Kodak 5071 (Ektachrome Slide Duplicating Film) was used for copying