UV Rodagon 60 mm
If you have access to a UV Nikkor 105mm, probably you don't need any other lens of this focal length for UV photography. However, this lens is expensive and difficult to find. Its focal length is also a bit too long for general-purpose photography with a DSLR. Photographers have recorded varying amounts of success with other lenses, and quite a few mention the EL-Nikkor 63mm f/3.5 enlarger lens in this context. A few have even removed the coating from older Nikkor lenses to use them for UV photography. However, these solutions (together with a few older lenses designed for UV work) suffer from varying amounts of focus shift, i.e., the image focused in visible light is not in focus in the UV range, and vice versa. Even a few old UV lenses are reported to suffer from focus shift. On the other hand, there are reports that the UV Rodagon 60mm f/5.6, a lens developed by Rodenstock for UV copy and microfilm work (and no longer produced since several years) displays no focus shift between UV and visible. Having a chance to purchase one of these lenses, I saw an opportunity to avoid the above problems, and to get a "real" UV lens.
I purchased my specimen from Dr. Klaus D. Schmitt, who runs a large web site specialising in macro lenses, specialty photographic lenses for scientific/technical use and related equipment. If you are looking for difficult-to-find and/or vintage equipment of this type, I recommend you try asking him. You may contact him through his web site.
Although expensive, the UV Rodagon 60mm costs roughly one-quarter to one-third of a UV Nikkor. It is, basically, an enlarger lens designed for a 1:8 optimal reproduction ratio, with a usable range of reproduction ratios between 1:2 and 1:20, according to the lens' technical data sheet. This sheet also mentions a UV Rodagon 80mm f/5.6, but I have not seen any (or even pictures of it). The 60mm uses a conservative design with 6 elements in 4 groups. I don't know if it uses special glass types for the lenses, but the lens coating must be optimized for UV transmission. The spectral UV transmission of this lens is discussed and compared with other lenses here.
A general statement one encounters in discussions of lenses for UV photography is that uncoated or single-coated (as opposed to multicoated) lenses are preferable. This statement should be qualified, because it applies only to lenses not designed for UV transmission. Single-coating and multi-coating alike can be designed for optimal UV transmission (or any other specific wavelength). The fact that the coating of general-purpose lenses absorbs UV is intentional. UV in outdoors photography is rendered as haze, and therefore it is desirable to eliminate it, usually with a coating on the front lens element optimized for this purpose.
The UV Rodagon 60 mm is equipped with a 35 mm filter mount (not the 34.5 mm filter mount found in some Nikon EL Nikkors). The lens attachment is a standard 39 mm thread. This lens needs adapters for mounting on a camera or bellows, and for using a filter of a standard diameter. It is shown above with a stack of two filter adapters and a Schuler UV filter mounted on a Nikon AF-1 filter carrier (I use the larger AF-2 for IR filters).
An interesting characteristic of this lens is that, when focused at infinity, it can be mounted on a Nikon body with roughly 8mm to spare between the camera and lens mounting flanges. Thus, a very short helicoid ring or bellows allows this lens to be used for landscape and general-purpose photography.