The El-Nikkor 50mm f/2.8 is a high quality 6 element enlarger lens that is ideal when reversed for extreme macro and my preferred choice for 1:1 to 2:1 magnification. They are quite cheap to buy and very good value for money.
Enlarger lenses are a boon. Because of the virtual death of film, you can pick up amazing lenses that used to go for 300-1000 Euros for a few euros on eBay, 25-50 Euros for really good ones is typical.
Good enlarger lenses are built to very high precision, often much higher than "general purpose" photographic lenses. Nikon used to churn out over a million 50mm f1.8 lenses a year, for 69 Euros each. At the same time, they were building the slower, simpler 50mm f2.8 El-Nikkor enlarger lens and selling it for 325 Euros. Part of that price difference is simply the smaller quantity. But part is the higher precision with which they made the El-Nikkor.
I have used this lens for standard photography as well as for macro and IR photography. The lens has a M39 mount, which can easily fit into an adapter to convert it to a more usable M42 mount for fixing to a 42mm helicoid.
With its four-group, six-element structure, the El-Nikkor 50 mm f/2.8 has always been highly regarded for photographic enlargement use.
During development of the lens, a certain German optical manufacturer secured the patent for its basic design. This meant Nikon (then known as Nippon Kogaku K. K.) was forced to incorporate methods that did not violate this patent into its design. There were numerous restrictions to overcome before Nikon could complete its optical system.
Nikon produced both an El-Nikkor f/4 and an El-Nikkor f/2.8. The El-Nikkor 50mm/2.8 is a 6 element, 4 group design, and the 50/4 is a budget version - a 4 element, 3 group design. I have tested both lenses here.
The El-Nikkor 50 mm f/2.8 is considered much better for extreme macro than the 50mm f/4
Every El-Nikkor lens is corrected for chromatic aberrations beyond the visible spectrum and into the near-ultra-violet wavelengths, which photographic papers for which they were intended, are particularly sensitive to. This makes them excellent lenses for UV photography where standard lenses are often coated to restrict UV and also are not corrected for these non visible wavelengths.
Nikon also states that as a result of special optical glass and matched coatings, the El-Nikkor lenses have ultra-violet transmission characteristics (in the 350nm to 450nm range) that are favourable enough to allow them to be used to make colour separations, in addition to all other enlarging applications.
