Rodenstock is one of the few companies that still produce anodizing lens. The Rodagon WA 40mm f4 is a lens that will compete with the Nikon El-Nikkor 50mm f2.8N in handheld. They’re the same as the size. Bayonet and filter diameters are common, M39 and 40.5mm. I’m not so sure which is better. But Rodagon is a new lens, more successful in contrast and color.
After using this lens for a while, it became one of my favorite equipment. 40mm gives more magnification than 50mm. Since this lens provides brighter viewfinder, I don’t use the Rodagon 28mm much. El-Nikkor 50mm and Rodagon 28mm are my backup lenses now.
40mm can be a bit too much for handhelds, we need to use it with short extension tubes. For tripod shooting, it can easily reach high magnifications and it gives very good results. If you want to create a set, it is possible to shoot in a very wide magnification range with two enlarger lenses at 80mm and 40mm focal lengths.
The Rodagon WA 40mm is already a very good lens in terms of sharpness. It also doesn’t have a noticeable problem with CA color fringing.
40mm is a small, rare and slightly high-priced lens. Do not try to replace your other 50mm enlarger lenses (like Rodagon, Componon-s or similar quality). You won’t feel a big difference. But if I only have to choose one, of course, I’d prefer the 40mm.