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Karl Lee

What's the Appeal of Kern Lenses?

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I was looking through active and sold listings of PL mount lenses on eBay, and I stumbled on some Kern prime lens listings and was surprised to see that some are selling for nearly $1000, and in some cases, well over $1000. Granted, Kern glass is generally regarded as being excellent quality, but aside from those still filming with Bolex cameras, is there much of a use for these vintage lenses elsewhere or in the digital realm? I think the fact that most of them are C-mount might be a big limiting factor, and I'm guessing that many of the Kern cine lenses aren't even S16 safe, which would make them all the more limiting for use in film or digital.


Also, didn't some of the Kern lenses have some type of integrated optical adjustment to compensate for light loss from the Bolex beamsplitter? If so, wouldn't this affect the accuracy of the lens aperture markings when used on a non-Bolex camera?

Edited by Karl Lee

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Your points and insight are all on the nose.


It's mostly hipster caché - they do look very nice too, good engineering, and perpetually dwindling quantities...

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They have found a second life beyond Bolexes on things like the BlackMagic Pocket and digital Bolex, but mostly I think on Micro 4/3 cameras for still photography, where people have been collecting C mounts for their high speed and interesting look, as well as the retro appeal of solid and well-made old lenses. Certain lenses have developed something of a cult status and are fetching pretty ridiculous prices.


Most if not all Kern primes do actually cover S16, the 10mm only barely though.


The RX range of lenses made for reflex Bolexes were designed to compensate for the aberrations introduced by the roughly 10mm thick glass prism in the light path, not the light loss. The aperture marks describe the geometric apertures just like any other lens marked in f stops.


I did a technical comparison study comparing the actual differences between certain RX and non-RX lenses, in part to try to understand why RX Kerns were still fetching high prices when they were patently not being used just on reflex Bolexes. What I realised was that the optical low pass and IR filters in digital cameras has the same sort of effect as the Bolex prism, although they are generally much thinner, in the range of 2 to 4mm thick. The thickest filter stacks are in the M4/3 cameras, roughly half that of a Bolex prism. So on those cameras both RX and non-RX lenses have a more or less similar aberration effect, either under-corrected or over-corrected. It's possible that the aberrations are even part of the attraction for photographers looking for unusual image effects.


For lens geeks :) the comparison study can be found here:


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You have a number of prime 16-mm. film lenses that are very similar in design, the six-element double-Gauss systems, Zeiss Planar derivatives. Among the one inch or 25 mm focal length lenses there are the TTH, Schneider Ciné-Xenon, Angénieux S41 (IIRC), Rodenstock Heligon, Leitz Summar, Berthiot Cinor, Kern Switar, and more. Older Kern have brass and or bronze mountings while Schneider, Angénieux, Berthiot, Dallmeyer, and Leitz employed aluminum, anodized aluminum in later years. Kern also changed to aluminum in the 60s. I think it is the heavy metal make that has become so attractive.


The Switar 25-1.4 is not fully corrected. The Switar 26-1.1 RX is an apochromatic lens and therefore more expensive. But one pays a price for the wide opening. The Kinoptik 25-2.0 Apo lens doesnt’ have the same softness.


I’m in this subject since years and always come to the conclusion that the main technical problem with motion-picture machinery is film flatness. To be precise, non-flatness. The film has room to move and it can behave in a complicated manner in the various cameras. When I measure a piece of polyester-base 16-mm. film I regularly find 15,95 mm as prescribed by the standard (ISO 69). Triacetate-base film can be shrunk down to 15,92 mm width and many a camera won’t guide a strip that narrow. The complicated film run may still prevent the film from swaying about but flatness within, say, two hundredths of a millimeter or a mil is no longer secure. Eclair, Aaton, Arnold & Richter, Photosonics, Paillard, Mitchell, Bell & Howell, Fairchild, they also just put their pants on one leg at a time. Any discussion of lenses is void if a camera is malfunctioning. I have found Bolex with too long FFD (wrong shim), with an aperture plate that has a raw front surface, with too wide an aperture plate which prevents the blade springs reaching the film edges, and more such stuff.




Here we read 16,020 mm. The upper limit of film width is 15,975 mm. Funny, isn’t it?

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