Pekka Buttler, August 2023
Set lenses are lenses where – using interchangeable parts of a set – you can build lenses for various purposes. Set lenses had some popularity in the 1950s and 1960s, but have since fallen out of use. Read on to find out more.
What are set lenses
A set lens is defined as a system wherein the lenses that are intended for picture-taking are created by combining two (or, thoretically, more) parts of a lens. The concept is maybe best illustrated by an example:
In 1954 Kodak Germany launched an update to its existing line of Kodak Retina rangefinders. The new Kodak Retina IIc and IIIc (which I will refer to Kodak Retina c) models both used set lenses. Out of the box, the Retina IIc/IIIc came with a 50 mm f/2.8, but the front party of that lens could be removed and exchanged against a front party that resulted in either a 35 mm f/4 or a 80 mm f/4 1.
The Zeiss Ikon Contaflex III camera was launched in 1956. When you got your copy, it came attached with a Zeiss Tessar 50 mm f/2.8 lens. However, the front-element of that lens was removable (the front element had a bayonet mount), and you could instead mount a range of alternative front-ends, thereby turning your standard lens either into a moderate wide-angle or a tele lens. Zeiss called this series the Pro-Tessar and offered 35, 50, 85 and 115 mm focal lengths (See here for a copy of the original manual).
Canon offered something very similar with their EX-series of cameras and lenses, offering 35, 50, 95 and 125 mm focal lengths. The EX system was originally launched in 1969. While the Zeiss Ikon Contaflex offered a bayonet to facilitate fast switching of lens front-ends, The Canon EX system used a 39 mm thread. (See the JAPB article on the Canon EX mount)
In both the case of Canon EX and Zeiss Ikon Pro-Tessar, the rear-end of the set lens was mounted permanently on the camera body. Similarly, in both cases the rear-end by itself was insufficient for taking pictures, and the lens needed to have some front-end as well.
The rationales for set lenses
There are some goals that a manufacturer may want to achieve by using set lenses.
Firstly, to take the Canon EX line as an example, it is possible to re-use the rear optical elements of a standard lens and make the lens into a moderate wide-angle or moderate tele simply by switching out the front lens group(s). Doing so will technically offer a way to save on the amount of glass in each interchangeable lens and save on weight and create cheaper lenses.
Secondly, and using the Contaflex as an example, the set lens may be a sweet–spot solution in balancing the needs of a leaf shutter SLR camera and an interchangeable lens camera as this technically enables an interchangeable lens leaf shutter camera where some of the lens elements are between the leaf shutter and the film plane. (The same argument also applies for the Kodak Retina c’s)
Thirdly, using the Canon EX as an example, using set lenses allows you to design lenses in such a way that the aperture mechanism is simultaneously an integral part of the camera body (hence offering better control over the aperture and thereby better auto exposure) while still being in its proper place (between the lens elements).
Finally – should one be so inclined – a set lens attachment system may offer an ipso-facto lens mount that 3rd party manufacturers cannot simply add to their repertoire of supported lens mounts (lenses would have to be redesigned).
The case against set lenses
There is one factor against set lenses above all other, so I’ll only mention that: Far from optimal lens designs.
As the examples of the Pro-Tessars and Canon EX’s shows, it is indeed possible to design a range of 35–125 mm lenses that all have the identical rearmost optical elements (3 elements in 2 groups). But if you’d take a look at the schemata of a lineup of high-performance 35–125 mm lenses, you’d notice that they have relatively little in common. In short, designing a range of lenses with the constraint that they must all share a common back-end leads to designs that are – to be frank – a kludge
Taking the obvious example of the medium tele lenses (whether Pro-Tessar 115 mm or Canon EX 125 mm), the optimum (for the 1950s–60s) design for such a lens is some derivative of the Sonnar design or even a version of the Planar. Using either design it is possible to reach maximum apertures in excess of f/2.8 while still having a well-corrected, relatively light lens.
But having a 3 elements in 2 groups design as part of the body effectively makes a Sonnar–based design impossible, and while that unavoidable 3 elements in 2 groups might be fundamentally compatible with a Planar-like design (as it was in the Canon EX), those rear lens elements do not support a bright tele Planar (they would need to be a lot bigger, which again would not be good for the standard lens.
As a result of this, the tele-versions of the set lenses were both big, heavy (> 400 grams for the front-end) and not very bright (f/3.5 in the case of the Canon EX125 mm; f/4 with the Pro-Tessar 115 mm).
What are not set lenses?
There is some similarity between set lenses and all those situations where you can modify an existing lens e.g. by:
• attaching a teleconverter between the lens and the camera
• attaching a wide-angle / fisheye converter into the lens’ filter threads
• attaching a close-up lens or soft focus filter to modify the lens.
Even though it might be an insignificant distinction to some, these do not technically qualify as set lenses, as:
• in this example you can also use the lens without modification (teleconversion/wide-angle/close-up)
• a set lens is characterised by that the lens will only work when it combines two parts of a set (at minimum, a front-end and a back-end).
Epilogue
In something of an odd twist even Nikon introduced a couple of set lenses, and did so as late as the mid 1990s, but the Nikon Fun Fun set was clearly aimed at educational purposes and is clearly an outlier (However, you can read more here, and here).
P.S. If you know of further examples of camera systems that used set lenses (beyond Canon EX, Zeiss Ikon Contaflex and Kodak Retina c), be in touch.
Footnotes
1 In a twist that perfectly illustrates the state of the West German camera industry: You could buy your Kodak Retina IIc/IIIc cameras using either a Rodenstock 50 mm f/2.8 Retina-Heligon C set lens or a Schneider-Kreuznach 50 mm f/2.8 Retina-Xenar C set lens. Then you could extend that camera using either a tele- or wide-angle front end. While Schneider-Kreuznach and Rodenstock had co-operated on the development (they are – for all intents and purposes – optically identical) of these front-ends, they were nevertheless mutually incompatible (there was a minor difference in the mount). Hence,
• if your Kodak Retina c came with a Rodenstock 50 mm f/2.8 Retina-Heligon C, you could use the Rodenstock 80 mm f/4 Retina-Heligon C or the Rodenstock 35 mm f/4 Retina Heligon C,
• if your Kodak Retina c came with a Schneider-Kreuznach 50 mm f/2.8 Retina-Xenar C, you could use the Schneider-Kreuznach 80 mm f4 Retina-Longar-Xenon C or Schneider-Kreuznach 35 mm f4 Retina-Curtar-Xenon C,
but none of the competition’s lenses.