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using m42 to c-mount adapter on bolex?


Mike Stoltz

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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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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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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:

 

01.jpg

 

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

 

116967.jpg

 

(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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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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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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  • 8 years later...
On 4/17/2011 at 5:20 PM, Mike Stoltz said:

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:

 

01.jpg

 

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

 

116967.jpg

 

(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

Hi mike! Did you ever end up doing this? I’m considering it too and was wondering how it worked out and how you fixed lens support!

thomas

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On 4/19/2011 at 10:01 AM, Ian Cooper said:

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

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.

well, there might be issues of the lens's back part fitting well enough inside the adapter. This has to be actually tested to ensure compatibility, there is no way to know any other way. The adapter and lens inner geometry may be such that it either works or not. If it does not, it is probably going to be way off, like the lens not being able to screw in even half of the required depth. But you should really just purchase a adapter and test this if you already have the lens. The adapters are cheap and you will have other uses for it even if it does not work with that particular lens. 

As for using heavier lenses with a Bolex, yes you will definitely need some support for it. For the lighter ones it may be enough that one screws in the special support plug which locks the bottom corner lens port of the turret to the camera body. For larger lenses additional support may be necessary. Don't use zoom lenses without at least having that turret locking screw in place, the turret will not stay at correct alignment and the FFD will change continuously when a gap develops between the turret and the camera body because of the strain. 

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On 4/17/2011 at 7:05 PM, John Sprung said:

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.

Theoretically yes. Wide angle lenses designed for 35mm SLR still cameras are generally retrofocus - otherwise known as the reverse telephoto lens design. Indeed a compromise in optical design.

However, having said that, Ive seen some impressive looking footage shot with a Bolex H16 with a 20mm lens from a 35mm SLR (mounted with an adapter.) Imagery was crisp with nice detail. Long shots looked good in terms of sharpness (as did the mid shots and close ups.) So despite the design of the lens, it performed well on a 16mm movie camera. Then again, I suspect the operator may not have infinity focus so that's one drawback. 

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By the way, Ive mounted long lenses from 35mm SLRs on my K3 (which has since died.) A Takumar 200mm and Tamron 400mm. They were used exclusively for filming wildlife. Results were quite respectable though I was expecting more from the Takumar with regards to sharpness. I haven't seen any of this equipment in years and Ive only just come across them again recently in storage. I might possibly sell the K3 for spare parts. 

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