EL-Nikkor lenses in UV photography
The EL-Nikkor 63 mm f/3.5 is reported by several web sources as a particularly good lens for near-UV photography. I also encountered, on web sites and bulletin boards, statements saying that other models of EL-Nikkor lenses (in particular, more recent ones) and other focal lengths (both shorter and longer) are much less suitable. To tell the truth, there are also contributions to bulletin boards stating that other EL-Nikkor models are just as good as the 63 mm f/3.5 (or at least, that they transmit very similar amounts of near-UV). Some of these latter statements are backed by actual measurements (especially this one).
On another page, I tested the El-Nikkor 63 mm f/3.5 and its more modern counterpart, the EL-Nikkor 63 mm f/2.8 A. I found that the older model is slightly better in terms of contrast (apparently for the reason that it is less sensitive to near-IR contamination), but the difference is quite small. Since the older model is, usually, at least four to ten times more expensive than the modern one, the latter may in fact be a better choice. The modern model also performs slightly better than the old one in photomacrography.
Given these results, it would seem that statements on the web about the 63 mm f/3.5 being "special" (as opposed to other, less suitable EL-Nikkors) need some testing, in order to be verified or rejected. Since I have several EL-Nikkor lenses, in which I have an interest as a collector, as well as equipment for UV photography, I am in a position to carry out these tests. My collection of EL-Nikkors is far from complete, but I selected and tested nine of them, all frequently available on the second-hand market. I decided not to test EL-Nikkors of long focal lengths, because they would require special equipment (they use very large retaining rings and filter mounts). In any case, there is little reason to use them for UV photography. Some of them could could be used as telephoto lenses, but would require special bellows.
My interest in EL-Nikkors as lenses for UV-photography is exclusively practical. No matter what a spectrometer may say, I am only interested in the pictures produced by my camera. It is completely irrelevant to me, for instance, whether a lens transmits large amounts of UV at 250 nm, given that my camera seems to be only sensitive down to roughly 350 nm.
EL-Nikkor lenses have been manufactured for over 30 years, in a few successive series. The models tested here are from three series, from older to younger:
I have every reason to believe that EL-Nikkor lenses not tested on this page would perform in a way similar to the ones described below. Most EL-Nikkors use very similar 6-element, 4-group designs. The 75 mm f/4 and 50 mm f/4 use a simpler 4-element, 3-group design. The 63 mm models have a slightly tweaked 6-element, 4-group design, albeit not substantially different. Therefore, all the 6-element lenses should perform rather similarly, with larger differences possible among the 4-element models. In addition, there are reports that a 240 mm EL-Nikkor also performed well in UV tests. EL-Nikkors with long focal lengths use a similar 6-element, 4-group formula, but some of their elements are very thick.
EL-Nikkor lenses differ from most other enlarger lenses, because the EL-Nikkors are specified as color-corrected in the 380-700 nm range (the visible range is 400-700 nm). There is a "web myth" about the 63 mm f/3.5 being corrected down to 350 nm. I further elaborate on this, and its likely origin, here.
As a subject, I used a lone flower that happened to emerge from the snow in my garden (not much choice this time of the year). An 11,000 K xenon HID provided illumination, and a Schuler filter was used to restrict the wavelength range to near-UV and a little indigo. UV is recorded as purple and brown, indigo largely as blue. The pictures are not post-processed. You can read here about precautions to take in UV photography (both for your safety and for good results). All lenses were tested at f/11 with the same exposure time (30 s). I used the same bellows extension for all lenses, which results in the magnification varying among lenses.
The above picture shows the line-up of lenses tested on this page. As a comparison, I also tested a UV Rodagon 60 mm f/5.6, which is designed for near-UV repro work. I included in the test also a Micro Nikkor 70 mm f/5, although this is not designed for UV use. This lens has a M39 attachment, and therefore can be used with the same accessories as enlarger lenses.
From the left, front row:
(not in the picture) Nikon EL-Nikkor 80 mm f/5.6 N
Days after taking the above pictures, I received an 80 mm f/5.6 N, which I tested with a different subject. In the following pictures, I compare this lens and two others at f/8, with a variety of filters. The UV pictures were taken with the same HID light of the preceding tests. All other pictures were taken with a 40 W incandescent lamp. The HID was hand-held, so there are unavoidable small differences in shading. The extension tubes I used in this case did not match the flexibility of bellows, so I could not obtain the same magnification with all lenses.
My reason for using extension tubes instead of bellows is that I discovered that many materials used to make bellows are translucent in near-IR, thus contributing to IR contamination of the pictures.
As already verified in earlier tests, the EL-Nikkor 63 mm f/3.5 and f/2.8N perform well, with the f/3.5 being slightly better.
The El-Nikkor 40 mm f/4N displays a somewhat lower contrast, but pictures could be post-processed in this respect. The short focal length makes this lens interesting for high-magnification work when reversed on bellows.
All 50 mm EL-Nikkors are good performers, but the older series 50 mm f/2.8 and the newer (N) series 50 mm f/4 have a higher contrast. The 50 mm f/4 N, in particular, is comparable with the 63 mm f/3.5 in practical results.
The EL-Nikkor 75 mm f/4 is the best of these EL-Nikkors, quite similar in fact to the UV Rodagon. This focal length is also most practical for close-up photography, because of the slightly higher working distance and the capability to focus at infinity if mounted on a very short focusing helicoid. I would rate it as better than the 63 mm f/3.5 because of the brilliant highlights of the leaves of the test subject. This is not to say that the UV Rodagon may not have an edge over the El-Nikkor 75 mm at shorter UV wavelengths. However, this is irrelevant in my case, since my camera does not record information in this extended range. At present, I don't have an EL Nikkor 75 mm f/4 from the N series to test. Both old and new specimens of this focal length are cheap and easy to find on the second-hand market.
The Micro Nikkor 70 mm f/5 transmits less UV than EL-Nikkors, and does not perform very well. The indigo is almost totally absent in test pictures with this lens, indicating little or no UV information is present. Clearly, not all lenses are suitable for UV photography, even among lenses that are very good in other respects.
The EL-Nikkor 80 mm f/5.6 N also turns out to be in the same class as the EL-Nikkor 75 mm f/4 and EL-Nikkor 50 mm f/4 N. The tonality of pictures taken with the 80 mm is very close to that of the UV Rodagon.
Much of the "fogginess" displayed in the center of the flower in most pictures is caused by near-IR contamination. This area happens to be very bright in near-IR. The UV source used in this test produces only little near-IR, and the Schuler filter again cuts at least 96% of it. However, any near-IR left over does have a visible effect, because the camera sensor is extremely sensitive to it. A Baader UV filter (which transmits even less near-IR) and an additional IR-mirror on the light source might improve the results. Finding a reasonably priced, heat-resistant near-IR mirror that does not absorb UV, however, is going to be difficult.
Shooting at f/8 or f/11, focus shift was not a problem with any of these lenses. This seems to confirm that EL-Nikkors are indeed colour corrected in an extended range. There are hints that the Micro Nikkor 70 mm f/5 may suffer from focus shift, though, with the UV focus plane being slightly in front of the visible one.
EL-Nikkors in hindsight
It has been a few years since I tested and used EL-Nikkors in UV photography as described on this page. Subsequently, I "graduated" to better UV lenses, at present foremost the Jenoptik CoastalOpt 60 mm f/4 Apo Macro and one or another of the "accidental" 35 mm UV lenses. The CoastalOpt is designed for multispectral photography, the 35 mm lenses just happen to be usable in UV photography. Both lens categories give substantially better results than the EL Nikkors if you need to record shorter wavelengths than 360-370 nm. The EL-Nikkor 63 mm f/3.5, which I tested together with the 35 mm lenses, did not fare too well. However, as a first and cheap lens to try UV photography, I still recommend one of the EL-Nikkors discussed on this page.
There are small differences in performance between older and newer EL-Nikkors of the same focal length and maximum aperture. Sometimes the older ones are better, sometimes the newer ones (as an example of the latter, the 50 mm f/4 N). I found no evidence that some EL-Nikkor models are unsuitable for near-UV photography - they all perform well (with the noted small differences), and they all transmit the same amounts of near-UV light (as far as visible in my test pictures). Any difference in UV transmission in the range relevant to me is probably less than half a stop.
Among EL-Nikkors, with the 75 mm f/4, 50 mm f/4 N and 80 mm f/5.6 N we have three top winners among a team of all-winners. Buy a cheap EL-Nikkor 75 mm f/4 if you want to be sure you have an excellent, cheap and versatile UV lenses. Choose another EL-Nikkor focal length if more suitable for your needs. Even better, buy several EL-Nikkors of different focal lengths. You don't need to pay 800-1,000 US$ for an EL-Nikkor 63 mm f/3.5, when you can get slightly better results with a 25 US$ EL-Nikkor 75 mm f/4 or 60 US$ EL-Nikkor 80 mm f/5.6 N.
If prices of the 75 mm should start going up as a result of this page, like those of the 63 mm f/3.5 did when it became "fashionable" for UV photography, buy an EL-Nikkor 50 mm f/4 N instead. Buy an EL-Nikkor 80 mm or 105 mm if you want a longer focal length. There are essentially unlimited numbers of these lenses out there. The truth is now out of the box.