It's been decades since I did any but, I do remember "mapping" the finished image being a big help.
1) Focus the main negative onto a white sheet of paper. Trace the outline of the image part you want to use. Mark the enlarger column height with a piece of tape, or marker.
2) Repeat the process with the other negative(s) for the finished piece, remembering to mark the enlarger column height.
3) When you get ready to make the print, make sure the paper is all the way to the right (or left) in the easel. Also, have an empty paper box to place the paper in between exposures, so you can focus the next negative. Just make sure you place the paper in so it is aligned the correct way for each subsequent exposure.
If you like Jerry Uelsmann's work like I do then setting up a few enlargers, learning how to make masks , soft edge and hard edge, seeing through your montage to understand where you need to block and where you need to allow light through is important.
some of the tools would include,,, red ruby, pos and neg lith film, diffusion tissue to soften edges, very sharp knife with good magnifying glasses, different types of receiving film if required, and an incredible amount of patience.
Jerry is the king of montage, and when they made features in PS for blending images , all the concepts came from his magic.
Originally Posted by Mainecoonmaniac
I've done the "add a different sky" print before now - It is very much easier to set the negs up in separate enlargers and fine tune the masks with test prints. I had the masks set a couple of inches below the enlarger lens to avoid any hard joins.
Also had an issue with the halo effect when masking out an area for some dodge/burn/contrast trickery - A bit of time with some spotting ink reduced the halo to barely perceptible proportions.
I can't find it right now, but there's a book by Uelsmann (can't find it right now) where he describes how he does them. Other books may have more details and more methods, though. I've thought about it, but haven't tried because I haven't come up with a good idea and images to do it with.
google Bob Pace, he wrote books on commercial photmontage.
according to the internet, everyone who currently uses a digital camera used to knock these out just like they do now in Photoshop... yeah right!
Well, to be honest there was nothing unusual about putting together finished results by compositing, sandwiching, combining and so on. It may seem shocking, but there was art between cave-paintings and Fauxtoshop.