How do they perform for film scanning? I had read you have to use them backwards for best results.
I use a EL-Nikkor 50mm f/2.8 reversed with a small extension tube, it’s almost 1:1. Quality is good corner to corner even with balsam separation on my lens.
Focus is very critical so you have to use a macro rail.
You can use an enlarging lens but it should indeed be reverse mounted for best results. An enlarger lens is better than a standard camera lens for film scanning. A good macro lens is better than an enlarger lens. A scanner lens is better than all of them. Period.
I’m using a Schneider Componon-S, 80mm f4 coupled to an Olympus Auto Bellows, with outstanding success. This is all mounted on a Sony A7riii and the lens is not reversed.
You can read extensive tests of many kinds, models and makes of lenses, including enlarging lenses, at https://www.closeuphotography.com/ and https://coinimaging.com/. Generally, enlarging lenses are not optimized for 1:1, or 1:1.5 for smaller chip cameras, and don’t do as well as lenses optimized for duping. These experts do have applications for enlarging lenses at higher magnifications, but not for most of us digitizing film at 1:1.
It depends on how you define outstanding success
I guess that I should probably defer to your definition, since you appear to have a much more defining interpretation of the term.
True, success is subjective.
With respect, for better results, the Componon-S 80mm F4 should really be reverse mounted. If you think about it, camera scanning is the reverse of darkroom enlarging and the rules of physics/optics will always prevail.
Reversing an enlarging lens for 1:1 duping makes no difference that I have ever observed in my own experience or read about by anyone, but I’d be happy to stand corrected with links to well-conducted tests. Caveat: most enlarging lenses of this type (Componon-S 80mm f/4) are symmetrical design, often six element, and optimized for somewhere between 8:1 to 12:1. So if you reverse mount it, you still have the same non-optimized problem. There are advantages to reverse mounting when going to higher magnifications. On the hopeful side, if you are using the 80mm lens for 1:1 duping of 35mm film, your lens extension is such that you are using the better-performing center portion of the lens with a very large image circle.