Data sheet: Topcon UV 50 mm f/2

Pekka Buttler, 08/2024 (updated 10/2024)

Specifications

The table below summarizes the lens’ key specifications (measurements based on pictured, last version of the lens):

Brand:	Tokyo Kogaku (Topcon)	Lens name	UV TOPCOR 1:2 f=50mm
Focal length(s)1	50 mm	Angle-of-view2	46,8 °
Maximum Aperture	f/2	In Production	1969–1974
Lens mount (this lens)	Topcon UV	Generation	Topcon UV
Length3	26,7 mm	Diameter4	60,1 mm
Filter ring diameter	49 mm	Weight	145 grams
Lens element count	6	Lens group count	unknown
Aperture blades (S/R/C)5	5 S	Focus throw	135 °
Minimum focusing distance	60 cms	Maximum magnification	1:9,9
Has manual aperture ring	NO	Has Manual focus ring	YES
Aperture mechanism type	N/A	Aperture click stops	N/A

Further notes:

• This lens was the second nifty fifty for the Topcon UV system. It was introduced in 1969 together with the Topcon Unirex camera and remained the kit standard lens until the Topcon IC-1 Auto was introduced in 1974.
• As with all Topcon UV lenses, this lens lacks an aperture ring (aperture was controlled on the camera). This has some implications for adapting (see below)
• While the mere measurements of the lens would indicate that we’re talking about a pancake lens, this is somewhat misleading as – thanks to the design of the Topcon UV system – all key controls (aperture, shutter speed, film sensitivity) are part of the lens mount. Hence, when mounted on a Topcon UV body, those control rings add 13 mm to the perceived ‘length’ of the lens.
• The filter threads do not rotate on focusing.
• My samples of the lens are somewhat⁶ radioactive⁷, meaning that one of the lens’ smaller, rear lens elements likely used thorium in the glass mixture.

Versions and variations

The original nifty fifty for the Topcon UV system was the 53 mm f/2 Topcon UV lens [data sheet], which was introduced together with Wink Mirror S camera in 1963. That design was replaced as the nifty fifty in 1969 by the 50 mm f/2 Topcon UV lens this lens, which was in turn was replaced in 1973/1974 with the Topcon HI 50 mm f/2, only to finally be replaced by the Topcon HI 55 mm f/1.8 [data sheet].

During the ≈5 years this lens remained in production it was manufactured primarily in an all-silver color scheme (see image above), but there also exist some, relatively rare copies that are all-black⁸.

History of Topcon

Unless you know your camera lore, you might not know that Topcon was once – between 1957 and 1976 – one of the foremost camera companies in the world.

You can read more details in the Topcon company profile.

Adapting

Adapting Topcon UV lenses is not especially easy, but this is not so much due to the lens mount. Technically the Topcon UV mount is very much like the DKL mount, and adapters for the DKL mount have existed for ages. Moreover, the Topcon UV mount offers a generous flange focal distance, making it relatively easy to manufacture adapters, even to SLR mounts.

The real reason why adapting Topcon UV lenses is relatively difficult is the simple weak availability of suitable adapters. It seems practically no-one bothered manufacturing adapters to allow the use of Topcon UV lenses on SLRs, and even with today’s most popular mirrorless mounts, you have to dig deep into aliexpress to find a metal adapter from Topcon UV to Sony FE/NEX (eBay has some 3D printed adapters).

(Remember that because Topcon UV lenses lack an aperture ring, that is a functionality that the adapter must supply.)

With these limitations in mind, below are (in the current state of affairs) the situation for adapting Topcon UV lenses.

This lens cannot be used natively on any current SLR or dSLRs. To use it in its native environment, you will need a Topcon UV (Wink Mirror S, Uni, Unirex/Unirex EE, IC-1 auto or new IC-1 auto) film body. While these were never produced in immense numbers, they seem to have stood the test of time reasonably well, and can still be found in a functioning condition.

While Topcon UV lenses are manual focus lenses, they lack an aperture ring. Hence, to adapt a Topcon UV lens to a mirrorless camera, you need an adapter that not only offers the correct mounting system and flange focal distance, but also allows you to control the Topcon UV lens’ aperture mechanism. As noted above, such adapters are available, but their availability is surprisingly weak. No special adapters (helicoid adapters, tilt/shift adapters) are currently available.

Using Topcon UV mount lenses on an SLR/dSLRs could be an option (there are no physical reasons why the mount could not be adapted), and Topcon themselves used to offer an adapter allowing the mounting of Topcon UV lenses on Topcon RE cameras. However, it seems that there are currently no adapters available. Moreover, as the rearmost element of many Topcon UV lenses protrudes significantly beyond the flange, it is not inconceivable that some Topcon UV lenses would (assuming there was an adapter) risk colliding with the mirrors on some dSLRs.

Footnotes

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1. Focal length is (unless stated otherwise) given in absolute terms, and not in Full-frame equivalent. For an understanding of whether the lens is wide/tele, see ‘Angle-of-view’. ↩︎
2. Picture angle is given in degrees (based on manufacturers’ specs) and concerns the diagonal picture angle. Rule of thumb:
   > 90 ° ==> Ultra-wide-angle
   70–90 ° ==> Wide-angle
   50–70 ° ==> Moderate wide-angle
   40–50 ° ==> ‘Standard’ or ‘normal’ lens
   20–40 ° ==> Short tele lens
   10-20 ° ==> Tele lens
   5-10 ° ==> Long tele lens
   < 5 ° ==> Ultra-tele lens ↩︎
3. Length is given from the mount flange to the front of lens at infinity. ↩︎
4. Diameter excludes protrusions such as rabbit ears or stop-down levers. ↩︎
5. S=straight; R=rounded; C=(almost)circular at all apertures. ↩︎
6. ‘Somewhat’ in comparison to most other radioactive lenses in my repertoire. In close vicinity to the rear of the lens, my Geiger counter registers ≈0,7 µSv/h, which is six times the natural background radiation around my house, but also only one fifth of figures for my most radioactive lens… ↩︎
7. Lenses being radioactive is not very unusual and is caused by the use of radioactive minerals (most usually thorium) in glass fabrication to tweak the refractive properties of lenses. See more in this JAPB article on radioactive lenses. ↩︎
8. These all-black versions of the Topcon UV 50 mm f/2 lens were likely sold bundled with the (equally less common) all-black versions of the Unirex body. ↩︎