BOLEX SBM S16 with modern S35 PL PRIMES

[Giorgio Taricco]

Hello guys,

lot of readings here about the bolex prism and infinity focus issue but I would like to know if someone have tried to use some S35 primes ( cheap modern set like Meike or Xeen) with Bosher or Kineco  PL ADAPTER ON BOLEX EBM S16. Asking just if they will work without problems knowing that would be better to use proper S16 lenses like OPTAR ILLUMINA etc… can get a couple of these primes for nothing so I’d like to try if they work.

Thanks!

Giorgio

[Dom Jaeger]

Sure they’ll work.

Using 35mm format lenses is identical to using S16 lenses, except that it’s harder to find wide enough focal lengths, and they are sometimes slower than dedicated S16 lenses. You can sometimes get unwanted light reflections due to the larger image circle, but I think you’ll be ok with a Bolex.

There is no “infinity focus” issue unless the adapter flange depth is off. The Bolex prism just introduces aberrations when used with lenses that have a shallow exit pupil - which is how deep the iris appears to be behind the rear element. It’s an indication of telecentricity, or how parallel the rays are coming out the back of the lens. And the aberrations diminish as you stop down. Anything over 50mm tends to have a deep exit pupil and is more or less unaffected. 

So you just need to watch out for lenses that have a shallow exit pupil when used at about T2.8 and wider.

Most PL lenses tend to be fairly ok, but I’ve seen footage from Zeiss Super Speeds used on a Bolex and at T1.3 some of the wides were noticeably softer than usual. By T2 they had improved a lot. By T2.8 they were pretty much normal.

So it’s more or less a lens by lens thing, and you need to test them individually to see how they perform at max apertures.