Data sheet: Jupiter-8

Pekka Buttler, 07/2023

Specifications

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

Manufacturer:	KMZ (Krasnogorsky Mekhanichesky Zavod)	Lens name	Юпитер-8 / Jupiter-8 2/50
Focal length(s) 1	50 mm	Angle-of-view 2	46 °
Maximum Aperture	f/2	In Production	1946–≈1985 (all variants)
Lens mount (this lens)	Leica thread mount	Other lens mounts	Contax/Kiev
Length 3	35,2 mm	Diameter 4	49 mm
Filter ring diameter	40,5 mm	Weight	123 grams
Lens element count	5	Lens group count	3
Aperture blades (S/R/C) 5	9 S	Focus throw	190 °
Minimum focusing distance	0,9 m	Maximum magnification	1:15,9
Has manual aperture ring	YES	Has Manual focus ring	YES
Aperture mechanism type	Manual	Aperture click stops	None (clickless)

Further notes:
• The Jupiter-8 is a Soviet version of the Carl Zeiss Sonnar 50/2. Just as the German original was produced for both Contax and Leica rangefinder cameras, so too the Jupiter-8 was produced for the Soviet versions of the Contax (Kiev rangefinders) and Leica (FED & Zorki rangefinders).
• The aperture ring is clickless and fully manual.
• KMZ was mostly responsible for manufacturing LTM variants of the Jupiter-8, while Contax/Kiev versions were produced at Arsenal in Kiev (alongside Kiev rangefinders).
• Importantly, some of the data in the table above does in no way apply to the Contax/Kiev variants: The Contax/Kiev variant does not have a focus throw nor a focusing ring (see here why)
• The lens was single-coated from the onset, but even though it remained in production until the mid 80s, it seemingly was never upgraded to multi-coating.

History of Jupiter and other Soviet lenses

If you’re interested, I recommend you read JAPB’s article about the Soviet lens ‘business’.

History of the Sonnar designs

The Sonnar designs were originally born out of necessity. Back before the invention of lens coating technology, each air-glass boundary represented a serious problem. Every air-glass boundary meant roughly 5% of the light that would hit such a boundary would be bounced back, instead of passing through the boundary. This not only meant that each air-glass boundary would decrease the amount of light that passed through the lens to the film plane, a goodly portion of that reflected light was liable to be bounced around within the lens, leading to veiling flare and loss of contrast. Hence, design a lens to minimise the number of lens groups was crucially important.

Until the invention of the Sonnar design, the only ways to produce large aperture lenses were based on the double-Gauss (a.k.a. Planar) and Ernostar designs, both of which were hampered by that the number of air-glass boundaries were relatively high (a minimum of 8). The Ernostar was the 1924 creation of the young (then only 23 years old) lens designer Ludwig Bertele for the company Ernemann. At the time of its launch it was – at f/2 – the fastest still camera lens in existence, and one year later Bertele bested his previous record with the f/1.8 Ernostar.

After Carl Zeiss acquired Ernemann in 1926, Ludwig Bertele continued pushing the boundaries and the Sonnar was a further development of the Ernostar. Not only did the Sonnar in 1932 manage to achieve an even larger maximum aperture (at f/1.5), it did so while simultaneously decreasing the number of lens groups to 3 (hence decreasing the number of air-glass boundaries to 6). It seemed like the perfect solution.

But it did not last long, Sonnar designs for standard lenses would never work on SLR cameras (that necessitated a significant back focal distance). Moreover, as lens coating technology advanced, one primary requirement for Sonnar-type lenses evaporated. After the war, Sonnar lenses remained popular on rangefinders (both as standard lenses and as short tele lenses).

Versions

Besides two significantly different versions for the two rangefinder mounts, this lens also progressed a bit during its close to 40 year production run. However, the pictured sample seems to be the most widely available variant.

Adapting

This chapter will discuss adapting the Leica Thread mount version of the Jupiter-8. If you’re interest in adapting a Contax/Kiev version, see the JAPB article on the Contax/Kiev mount.

To use this lens natively, you will need a Leica thread mount film body. This means either a Leica body from before the 1954 introduction of the Leica M-mount, a Soviet Leica (Zorki or FED) or one of the more modern Japanese LTM rangefinders. You can also use this lens on any Leica M mount body using the LTM-Leica M adapter ring.

Thanks to being a fully manual lens (manual aperture, manual focus), the lens can be adapted to all mirrorless cameras using a suitable adapter. Moreover, LTM lenses are so uncomplicated that a simple ‘dumb adapter’ will do the job perfectly. However, due to LTM mount’s relatively short flange focal distance, special adapters (helicoid adapters, tilt/shift adapters, speed boosters) are not an option.

Due to the short flange focal distance used by LTM cameras, there is no meaningful way to adapt this lens to any SLR or dSLR.

Footnotes

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. ↩︎