Will this lens work on a Bolex Rex 5?

[Daniel Meier]

I'm planning on getting this lens (mainly for my BMPCC):
https://www.bhphotovideo.com/c/product/1022991-REG/kowa_lm6hc_c_mount_6mm_f_1_8_16_1.html/reviews

I also wonder if it will get me a usable image on my Bolex Rex 5.
Maybe some of you can tell from the specs. Maybe some of you even used it before.

I am aware of the terms "RX- and Non-RX" lenses. But haven't yet dived too deep into topic. What is the downside of using this particular Non-RX lens on the Rex?

[Dom Jaeger]

I would be very wary of using this on a Bolex because the rear element protrudes so far back. The specs seem to indicate it protrudes about 6.4mm past the C mount flange, which I think will hit something before the lens properly seats. 
 

In terms of using non-RX lenses on a reflex Bolex, it depends on the exit pupil depth, but generally if you stop down a few stops the aberrations will be minimal. 

[Robert Hart]

Dom. I agree. The rear of the lens will bottom out on the structure beneath the C-Mount thread, possibly before the threads even engage. 

[Daniel Meier]

Thanks Robert and Dom for your help.

Where else could I get hold of a wideangle lens for the REX 5?
I already have a 10mm but I want to go even wider.

Nowadays on the web I can't seem to find anyone selling a Century 3.5mm or a 5.7mm.

Are there any other options out there on the market to go lower than 10mm on the Bolex H16 these days?

[Robert Hart]

There is always the Kinoptik Tegea 5.7mm lens in C-Mount like this one which should fit up as the rear optical elements are within the C-Mount. It confers a rectilinear image, which means neither barrel nor pincushion distortion will occur. All straight lines will be straight but the image will be diagonally stretched like you see in some news-camera wide-angle images.

There is also a slightly weird aesthetic effect on faces which appear to be narrower with eyes closer to sides of face. Speed of apparent motion towards or away from subject is accentuated. The lens was referred to for a while as "the Rodriguez Lens" as one was used by director Robert Rodriguez along with a zoom in his breakout film "El Mariachi."

The lens was a pioneer design and not the sharpest kid on the block by today's standards. It seems sweetest at about f5.6.

Angenieux made a 5.9mm lens in C-Mount. I cannot speak for the image quality, any distortion effects it may have or whether the rear elements extend beyond the C-Mount thread as I have not seen or handled one. so far as I know, neither the Angenieux nor the Kinoptik have a focus ring and rely on a very deep depth of field for clarity of the image.

https://www.ebay.com/itm/284871742341?hash=item4253add385:g:d-QAAOSwxGliuFLI&amdata=enc%3AAQAHAAAAsIPLo2te%2FMlS9OFKJy9AyOwQM%2BBZa%2FimpHto8LbJSxo2Y29I49aHkWoR3FPuOj1XA3T86Ze%2BLTji2n7rAv4%2BVQ5LDQPAhRQPG1x4EZPhVoXX%2Ff07%2BzvT6aq8BtAdzmjWLWBDQH8enTHHbCIXeH1EagC6T0Cu1E5kLoqX0sRKSayap7D6MkvLp8AU%2BTbwm6eGWvDGD%2BTyPBaLLFCOFiNREygeuHWUonISYlUgSrN2XTTM|tkp%3ABk9SR978mfPdYA

Edited August 30, 2022 by Robert Hart
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[Doug Palmer]

There's always the option of a Bolex Aspheron lens that fits on to the front of the 10mm.  Or a cheaper option is use the Super-8 version.  It's not quite as wide an angle but quite close.  You'll need a ring to attach it.

https://filmisfine.com/shop/camera-lenses/8mm-movie-lenses/bolex-aspheron-lens/

[Allyn Iwatsuru]

I made this mod for the meike 3.5mm which works great for under $200 

https://cinematography.com/index.php?/forums/topic/88096-converted-meike-35mm-m43-to-cmount-for-bolex/#comment-560123

Laowa has been making some interesting wide angle mft “cinema” lenses that I would like to check out and take measurements of to see if they can be modified in the same way.

[Daniel Meier]

Wow Allyn this looks amazing. Thanks for sharing. That is excactly what I am looking for.

Could you imagine modding this for me?
Of course I would cover all expenses and shipping.

Here's my mail so we could have further conversation outside off the topic:
daniel@framefive.de