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         Virtually all of the color photography I do professionally is on process E-6 transparency film. Rarely do I have much reason to shoot C-41 color print films. Usually the only occasions when I do are weddings (which are not a mainstay of my business) or events where I know that someone will want a print copy of virtually every photo I take. Otherwise, I'm shooting with the idea that I'm out to get that one shot in a few hundred that belongs in a magazine, catalog, or calendar.
         There are, however, occasions when the nature of the assignment might demand that I produce a photograph worthy of publication - while at the same time producing tens, or perhaps even hundreds, of prints for somebody's private photo album. Since the Ilfochrome color transparency printing process I run is time consuming (and for most folks, prohibitively expensive), what I do in these cases is shoot to a good transparency film to start, and I then duplicate these shots on a color negative film stock that can be easily machine printed at the corner drugstore. That leaves me the option of handing over the duplicate negatives and relieving myself of the hassle of all that printing -- or even dealing with a printer myself. And the holder of the negative can do all the abusive things to negatives that non-photographers (and even some so-called "pros") often do to them. After all, if the duplicates are destroyed, I will still be holding the original films.
         35mm film is actually a pretty easy thing to duplicate, provided you have the right equipment. In my case, this equipment consists of a collection of accessories for my workhorse Nikon F3HP camera. In figure 1, I show the entire rig as it's set up for duplication. There are essentially four major pieces of the assembly. At the back is the F3HP body itself. It is bayonet mounted to a PB-6 bellows assembly, and mechanically speaking, the bayonet mount supports the weight of the camera body behind it. The PB-6 also has at its base a monorail used for extending its bellows and a standard 1/4-20 threaded hole for tripod mounting. The PB-6 is often used for close-focus / macrophotography work, and in this case, the small object on which we're close focussing is the 36mm x 24mm image area of 35mm film.

 

 
Figure 1 - The Nikon F3 Duplicator Setup
 
         At the front of the PB-6 is the imaging optic itself -- in this case my standard Nikon 50mm f1.4 AI lens. The lens mounts directly into the bellows at the front. Note that although the F3HP is not an autofocus camera, even if I were to use an autofocus camera and autofocus lens, the bellows assembly would defeat the autofocus features. I have the lens focused at the shortest distance possible (in this case just under six inches).
         In front of the lens is a PS-6 slide duplicator, which comes with a holder for a slide or a negative strip and a bellows of its own. The second bellows is critical, since it's a combination of distances from the object to the imaging optics and the distance from the optics to the focal plane of the camera that will determine the image focus as well as the magnification of the original image. And without the second bellows, there'd be light leakage onto the image, resulting in a loss of color saturation and contrast.
         The entire rig is focused using the knurled knobs on the PB-6 monorail and the set screw that holds the PS-6 to the rail. In this case, I've got magnification set to where the original image almost fills the F3HP viewfinder. I stop short of a full fill, since I know that the F-series cameras are very precise in their image coverage, and what you see in the finder is pretty much what you get. (Other 35mm cameras tend to be a little sloppy in their finder coverage, and they usually only show you only 95%-97% of what you'll get on film; so you can safely fill the frame when working with them and count on the finder's "slop" to assure that you'll get everything in the original onto the duplicate. But the F3, by the very nature of its accuracy, is not so forgiving.) With things set this way, I use a fair amount of the front (PS-6) bellows, but actually very little of the rear (PB-6) bellows.
         One of the major optical concerns in this setup is keeping edge-to-edge image sharpness. And this is one of the places where you get what you pay for when you buy duplication equipment. The fact that the bellows arrangement shown here allows the use of a real Nikon lens in the middle helps tremendously. I've tried making internegatives using a screw-mount "all-in-one" duplicator (which is usually a tub with a cheap lens in the center of it), and keeping things sharp at the extreme edges of the photo with such a $75 el-cheapo setup is close to impossible. The combination of a PB-6 and a PS-6 will set you back $250 if you find them on the used equipment market as I did, and this doesn't include the cost of a good lens ($100 used) and an F3HP body ($500 used). But the results are noticeably better when you use a real lens, real bellows, and a solid metal monorail to keep everything aligned.
         That having been said, you're still best off setting the aperture of the lens to its most stopped-down position. In spite of the fact that the 50mm f1.4 Nikon AI achieves its maximum sharpness somewhere between f5.6 and f8, given depth-of-field considerations at the film edge, the entire system is maximally sharp at f16.
         This makes exposure times long, especially when you consider that the effective speed of the Kodak Commercial Internegative Film I use for this purpose is roughly (at least according to my experimental results - your mileage may vary) ISO 6.
         Well might you ask at this point why I don't just use a standard C-41 film that I can find at any drugstore and which would carry a speed rating of 100 or faster. The answer is that such films are likely to be far too high in contrast to be useful in this application. Recall that E6 process films (and in particular the RVP50 emulsion that I shoot) are extremely color saturated and contrasty. In order to produce a color negative that's even remotely printable, the C-41 process film has got to be low in contrast and color saturation. As a practical matter, there are a few slow speed "standard" C-41 color films that will suffice in a pinch (Kodak Royal Gold 25 comes immediately to mind). But by-and-large, given the choice, you're better off shooting a real internegative film, even if it means buying it in a 100' spool and winding it into its canister yourself. (And it probably will.)
         At this point, the astute reader is probably already thinking about color drift in the negative due to the internegative film being shot past the point of reciprocity failure. And the astute reader would be very correct in his concern. As a practical matter, following the "Sunny 16" rule, you could expect that ISO 6 film to demand a 1/6 of a second exposure time. But in reality, even if you point the camera straight at the sun on a bright, sunny day (and I do, although I protect my eyes with a set of welding goggles and I'm still damned careful when I do it), you're not really shooting a sunny scene. You're shooting through a diffusing glass and a piece of film. So you're likely to be shooting with exposure times of a second or two.
         As a result, most of the "dichroic filter pack" information provided by Kodak is going to turn out to be pretty useless. And in reality, you're going to have to experiment a bit to find the filter pack that works best for you. This is where having a good reference MacBeth slide (you do have one, don't you?) is going to make your life a good deal easier. For this shoot, knowing that I'd be sending my images to possibly a calendar manufacturer and a magazine publisher, I shot MacBeth images on location as a matter of course. But even if I hadn't for those reasons, having foreknowledge that I'd be making internegatives would have inspired me to make that extra effort.

 

 
Figure 2 - A MacBeth Chart on Original and Replicated Films
 

 
Figure 3 - The Model on Original and Replicated Films
 

 
Figure 4 - The Transparency Image that Went to the Printer
 

 
Figure 5 - The C41 Print Made for the Model