This is a comparison of three EL-Nikkor enlarger lenses for reflected UV photography.
The candidates are the older EL-Nikkor enlarger lenses: 4/75mm (black), 5.6/80mm, 5.6/105mm (both black/chrome)
[click on image to see a larger one]
These are UV-VIS differentials to show the possible focus shift (ghost images, white or black depending on direction of the shift:
left: 75mm, middle: 80mm, right: 105mm - identical exposure and processing for all.
And here the UV-VIS transmission graph of these three lenses.
It gets pretty obvious, that the 80mm is the clear winner, not only in terms of lack of focus shift, but also in UV transmission, since it has about double the transmission @365nm than the 75mm EL-Nikkor. No wonder actually, as the 75mm is a Tessar 4-3 design with one glued lens element, whereas the other two are double Gauss 6-4 designs.
P.S.: the 80mm EL-Nikkor (the older, chrome black full metal type) has an adapter ring on its base with outer M39x26tpi screw mount (Leica enlarger mount). Beneath it is a M32.5 x 0.5 thread meant to fit a shutter size 0. Company Schneider Optics offers adapter rings, if that one should be missing (oder code 92-010711
P.P.S.: the filter thread of that older EL-Nikkor 80mm is 34.5mm, which is pretty uncommon, Rafcamera.com sells a suitable adapter ring.
Stay tuned, more will follow on that fascinating subject...
More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos