Enna Lithagon 24 mm, 28 mm and 35 mm

Enna München made in the 160s and 1970s a number of 24 mm f/4, 28 mm f/3.5 and 35 mm f/3.5 lens models. Over the years, they were made available in a variety of barrel styles and camera attachments (mostly Exakta bayonet and M42). The number of diaphragm blades, in some cases, may also have changed with time. Their optics, however, remained fairly constant throughout their production period, with the exception of multicoatings sometimes becoming available toward the end. These lenses were also marketed as Porst and a few other brands, and issued in different barrels.

The Enna company still exists and still uses the original logo with a schematic achromat lens, but no longer manufactures camera lenses and its business is restricted to specialist plastic injection molding.

The lenses discussed in this page have been reported as usable in UV imaging. See, for example, the lists at ultravioletphotography.com. You may also search that site for posts that discuss specific models of these lenses. However, I can see a few problems with taking at face value these and similar lists of information on the suitability of lenses for UV imaging.

• Many of these legacy lenses have been made in multiple variants that may use different optics and coatings, but summary lists and statements on suitable UV lenses often make it difficult or impossible to identify which model/variant has been tested.
• Tests summarized in these lists have often been carried out by different photographers with different equipment, subjects, and illumination. Testing in different conditions gives different results.
• In particular, testing with a broad-spectrum UV source like sunlight or electronic flash and suitable subjects like UV-yellow and UV-blue flowers shows whether a lens is capable of producing sharp images in a range of different UV false-color that indicates a sufficiently broad UV spectrum. Testing with 365 nm LED torches, instead, only shows whether a lens can image subjects in a wavelength range between roughly 355 and 400 nm. UV LEDS are not monochromatic and emit a range of wavelengths with one rounded peak roughly 10-15 nm wide and a relatively long tail in either direction, of which the tail toward longer wavelengths is preferentially recorded in test images because converted cameras are more sensitive at these longer wavelengths.
• A measure of subjectivity is also involved in interpreting test results - what one photographer may regard as a satisfactory performance may be inacceptable to another photographer.

These problems can be alleviated by making more detailed information available on the tested lenses and on the test results. It is also good to be able to compare test images produced by different photographers with the same lens models.

Disclaimer

My interest in these legacy lenses is mainly in testing the most promising ones in digital near-UV imaging. I am publishing information about the external appearance of these lenses on this site, in order to allow the clear identification of which of the many models and variants I have tested in UV imaging. Performance in UV may be different in other variants and models, especially if they use different optics and/or different coatings.

Enna Lithagon 24 mm f/3.5

The Nikon HN-1 metal lens shade works well on this lens, but it easily causes dark corners if stacked onto a filter and the 24 and 28 mm lenses. This lens shade accepts a 72 mm butterfly lens cap, but a 67 mm butterfly cap also works.

Enna Lithagon 28 mm f/3.5

Porst Super Weitwinkel 28 mm f/3.5

Enna Lithagon 35 mm f/3.5

There is also a subsequent variant with automatic aperture that uses a different optical design, a different sculpturing of the focus ring, and focuses down to 50 cm. Numerous 35 mm f/2.8 variants branded Porst were also made. I have even seen a 35 mm f/3.5 branded Porst that is identical to well-known lenses with the same specifications made by Kyoei and branded in a dozen different ways.

General characteristics

All lenses discussed in this page have rear elements projecting behind the lens mount, which may touch the mirror of some SLR/DSLR cameras. The rear element is slightly recessed within its retaining ring, and it is safe to place the lens on a work surface with its rear portion lowermost. The 24 mm also has a strongly convex front element mounted close to the front of the barrel, but an ordinary butterfly cap can be used on this lens without touching the front element. To further reduce the risk of touching the front element of these lenses, I leave a metal lens shade permanently mounted on them, with a large butterfly cap at the front of the lens shade.

I did not mount filters on the front filter thread of lenses. Instead, I used M42 to Sony E (or Micro 4/3) lens adapters modified to carry built-in 30.5 mm filters.

UV Tests

For this purpose, I used a full-spectrum Sony A7 II and an M42 to Sony E adapter modified to carry a 1.25" Baader U UV-pass filter (re-mounted in a standard 30.5 mm filter ring) a short distance behind the rear element of the lens. To focus on a relatively small subject area, I added a 7 mm M42 extension ring between lens and adapter.

Images are cropped but not otherwise post-processed.

The flash power indicated in the figure caption is the power setting of the Bowens 1500 Pro studio flash (with original non-coated tube and tube shield by Bowens) used for the test image. Each unit in the power setting corresponds to one stop of emission power.

The 24 mm requires two more stops of flash power than the 28 mm to produce a similar exposure.

The 24 mm does display the UV signatures of the flowers, but produces almost no UV false color, other than blue and a very bluish violet. This lens is therefore limited to about 380-400 nm. Also, it displays some "flare" in the center of each flower, which is most likely a NIR leak through the UV-pass filter. The fact that flash power must be increased by about two stops to provide roughly the same UV exposure as the 28 mm agrees with this idea, because neither lens blocks NIR to a significant degree, and therefore the NIR to NUV ratio is sufficiently high in the image produced by the 24 mm to leak even through a good UV-pass filter like the Baader U.

 

The difference in false color can also be observed when the Lithagon 24 mm and 28 mm are used for UV landscape photography. Although for this application it is usually not necessary that the lens be capable of recording UV-yellow, images recorded with the 24 mm are almost monochromatic UV-blue (with a hint of UV-violet, mostly in the sky), while the 28 mm gives a more neutral false-color with easily distinguished UV-gray and UV-blue areas.

In conclusion, the 24 mm can be used in NUV photography only when a 24 mm focal length is required and a 28 mm is not enough, no UV false color is necessary, and a modest amount of NIR contamination is tolerable. The angle of view of the 24 mm is of coarse greater, but the difference in angle of view of the two lenses, in visual terms, is not that great. An additional problem with the 24 mm is that (across the UV, VIS and IR spectrum) its resolution at the edges is quite poor. In practive, with the 24 mm you gain a slightly wider angle of view, but the image periphery are visibly fuzzy and may force you to crop back the image to an angle of view comparable to the 28 mm.

- It is now known that there is a far better 24 mm lens than the Enna one, i.e., the Nikon AI-S Nikkor 24 mm f/2.8 (see for example here and here). This Nikkor lens is also generally cheaper and far easier to find than the Enna 24 mm. As a result, I no longer recommend the Enna 24 mm.

The Lithagon 28 mm, on the other hand, displays UV-blue, UV-violet and (to a lesser degree) UV-yellow, shows only a very faint NIR contamination, and is therefore usable when these three false colors are desired. This lens is the best 28 mm I tested so far in UV, and performs clearly better in UV than two variants of Super Takumar 28 mm f/3.5 that I tested separately.

The Porst 28 mm f/3.5 appears to be a rebranded Lithagon 28 mm in a different barrel. The two lenses are optically identical and produce the same results, but the Porst is usually cheaper. However, there are other Porst 28 mm lenses that evidently use different optics, which I have not tested. Most of these lenses are more modern and multi-coated, which may make them unsuitable for UV imaging. When purchasing a Porst lens (including the 35 mm discussed below), make sure you know which model you are choosing.

The Lithagon 35 mm f/3.5 has been mentioned by Internet sources as usable down to 320 nm. It has also been mentioned that this Lithagon performs better in UV imaging than the commonly available Kyoei-made 35 mm f/3.5 lenses. Several Kyoei and similar lenses with the same focal length and speed are known to give good results in UV imaging (see examples here), and most of them are cheaper and easier to use than the Lithagon 35 mm. The question is whether the Lithagon 35 mm provides advantages that can justify its higher price, scarcity, and problematic use.

My results do not agree with what I have read on other sites. The Kyoei 35 mm transmits about one stop more UV, and provides a better, more saturated UV-yellow. It also displays a more visible difference between the UV-blue of the daisy and the UV-violet of the background.

The Porst 35 mm f/3.5 (first two variants) appears to be a rebranded Lithagon 35 mm in a different, cheaply made plastic barrel. Also in this case, the Lithagon and Porst lenses produce the same results. The Porst is much cheaper than the Lithagon, but its internal mechanics are unreliable and often damaged. The Porst lens has a conventional preset aperture ring, which in theory should be easier to use than the problematic anterior aperture ring of the Lithagon 35 mm. However, in my specimen at least, precise focusing is difficult to achieve because the focus ring is a little too hard to rotate, and insufficiently dampened. The preset mechanism does not work properly in my specimen of the lens, although the aperture ring can still be used.

Summary

The Lithagon 35 mm f/3.5 and its clones are usable in UV photography and produce a moderately good UV false color, but Kyoei-made 35 mm f/3.5 lenses are better. The Lithagon 28 mm f/3.5 is the best legacy 28 mm lens I tested so far in UV imaging. The Lithagon 24 mm f/4 is not as good as the 28 mm, but is nonetheless one of very few 24 mm lenses usable in UV imaging (the AI-S Nikkor 24 mm f/2.8 is however better and cheaper than the Enna 24 mm).