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using m42 to c-mount adapter on bolex?


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#1 Mike Stoltz

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Posted 16 April 2011 - 09:02 PM

Hey all,

Trying to salvage the zoom lens off of a dead K3 camera, and was wondering if anyone has had any luck or if it is possible to mount this lens (m42 Pentax screw mount) using a Pentax-to-c-mount adapter? Any reasons why this is an ill-advised undertaking? Have at it, and thank you in advance.

Mike
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#2 John Sprung

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Posted 17 April 2011 - 04:35 AM

It would be an easy adapter to make, you have over an inch to work with, just shy of 28 mm, difference in back focal distance. Things to watch out for:

1. Supporting large and heavy lenses so the turret doesn't sag, and the adapter threads don't get damaged.

2. Available focal lengths will all be on the long side for the much smaller 16mm format. Wide angle lenses for the big still frame will have a lot of optical compromises you don't have to tolerate in C-mount lenses of the same focal length. Under about 40 - 50 mm, you're better off going with a lens designed for the 16mm format.

3. Because the Pentax lenses make a much bigger image than 16mm, matte out all that extra light so it doesn't bounce around and fog your dark areas.

Address those issues, and you're good to go.




-- J.S.
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#3 Mike Stoltz

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Posted 17 April 2011 - 10:20 AM

Thanks for the insight John,


I guess I should have been more specific. I want to use the 17-69mm f1.9 Zenit Zoom Lens off of my Krasnagorsk K-3 16mm camera. This lens is an M42 "Pentax" style mount zoom lens as seen below:

Posted Image

B+H offers an M42 to c-mount adapter that looks like this:

Posted Image

(item located here

Obviously I would need some lens support, but does anyone know if this mount would work? K-3s and Bolexes are so ubiquitous compared to other systems that surely someone has tried this before?

Thanks again

Mike
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#4 Ian Cooper

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Posted 19 April 2011 - 02:01 AM

Whilst it isn't something I have physically tried for myself, there's no reason why it wouldn't work.

The K3 lens is designed to cover reg-16, the only issue is the difference in mounts, which that adapter will sort. I've used a similar adapter to go from Minolta mount lenses to C-mount on my Beaulieu R16.

The only thing to watch, as John mentions, is to make sure you don't put too much strain on the mount - but that's something to be careful of with any heavy lens on C-mount.

Oh, and one other thing! If your Bolex has the reflex viewfinder then be aware that the Zenit zoom won't be optimised as per 'RX' style lenses designed specifically for the reflex Bolex.
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#5 Leo Anthony Vale

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Posted 28 April 2011 - 05:04 PM

Oh, and one other thing! If your Bolex has the reflex viewfinder then be aware that the Zenit zoom won't be optimised as per 'RX' style lenses designed specifically for the reflex Bolex.


This was gone over in the past, look it up in archives.
But if you're stopped down below f/3.3, 3.5, the problems disappear.

Bolex marked f/3.3 & f/3.5 Pan Cinor and f/3.5 Kern zooms which were not RX for use on the Rexes.
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