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C-mount adapter to lens compatibility
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Home Manual Focus Lenses  Cine lenses
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PostPosted: Thu Oct 14, 2021 8:42 pm    Post subject: C-mount adapter to lens compatibility Reply with quote
Apologies if this has been answered somewhere.

Some time ago I picked up a C-mount to M4/3 adapter, but I haven't yet bought any C-mount lenses (yes, sometimes I buy adapter for which I end up not buying any lenses).

My question is this:

Since C-mount has a smaller flange distance than M4/3, the adapter sits into the camera mount a little bit. So from the top of the adapter you have a ring that is "sunk in" to the adapter. At the center of that ring is the thread for the lens. I hope I haven't made my description too confusing.

I seem to remember reading somewhere that on some lenses the diameter of the part of the lens that fits into that sunken ring can be larger than the diameter of this section of the adapter, causing the lens to not fit.

Measuring my adapter (cheap generic variety), it has a small "lip" with a diameter of about 36.9mm and the larger sunken ring area (sorry, bad description; I lack the words to describe the accurately) has a diameter of about 39.9mm. Also, the 39.9mm part of this ring is not quite as deep as the 36.9mm diameter area which might cause infinity focus problems (2.78 vs 2.2mm deep)?

Sometimes I see interesting looking vintage C-mount lenses, for example by Schneider Kreuznach. But I am unsure if they would actually fit the adapter, and then also focus to infinity.

Can anyone offer any insight?

Aside, with an adapter as flat as the C-mount to M4/3 isn't it difficult to grab hold of the adapter enough to dismount it?

Regards, Christine


PostPosted: Thu Oct 14, 2021 11:17 pm    Post subject: Reply with quote
I think all my c-mount lenses would be narrow enough to fit within the deeper part of your adapter. However several need to be slightly unscrewed to reach the proper focusing distances, so might still reach infinity from the slightly higher ring.
The correct registration for c-mount is 15.526mm while MFT is 19.25mm showing the mounting surface for c-mount lenses should be 3.724mm inside the mounting surface of the camera body. Not an easy distance to measure on recessed adapters but you should be able to measure both surfaces from the front face & subtract one from the other.

Hopefully my late night rambling has helped, even if It's not a simple answer.
Mike


PostPosted: Fri Oct 15, 2021 5:18 am    Post subject: Reply with quote
The Bell & Howell C lens mount has the register of 0.69" or 17,526 mm.


PostPosted: Fri Oct 15, 2021 7:33 am    Post subject: Re: C-mount adapter to lens compatibility Reply with quote
connloyalist wrote:
. . .
Aside, with an adapter as flat as the C-mount to M4/3 isn't it difficult to grab hold of the adapter enough to dismount it?

Regards, Christine


The cheap, ebay C adapter I have fits snugly, but requires merely light effort to remove.
And the grooves milled around the face also help to give a better grip.


#1


PostPosted: Fri Oct 15, 2021 7:49 am    Post subject: Reply with quote
Thank you for your helpful answers Smile

Please do correct me if I get this wrong. The bottom of the flange of the C-Mount adapter is / should be the M4/3 flange distance of 19.25mm. The top of the deeper section of the adapter is the flange distance for C-mount. So we would need to measure how much lower the top of the deeper part of the adapter is than the bottom of the flange of the adapter, correct?

Re-measuring things here with my calipers I come to these numbers. The outer flange of the adapter is about 2.03mm thick. The bottom of that outer flange of the adapter should be the M4/3 flange distance. From the top of that flange the deeper section is 3.1 to 3.3mm deep depending on where you measure. So the C-mount flange would be 3.1 - 2.03 = ± 1.07mm below the M4/3 flange. 19.25mm - 1.07mm = ± 18.18mm. And that's not deep enough, so looks like I would need to get a different adapter because the lens would not reach infinity. Or am I messing things up here?

Regards, Christine


PostPosted: Sat Oct 16, 2021 6:55 am    Post subject: Reply with quote
If I may suggest something, get yourself a ciné camera that is made for C-mount optics. Much more joy.

    Ensign Kinecam Sixteen
    Beaulieu M 16, R 16
    Victor 3-4-5
    Kiew 16 Alpha
    Paillard-Bolex H
    ETM-P
    Bell & Howell Filmo 70-121-141-240-627
    Keystone
    GIC
    Doiflex-16
    Arco TV-16
    Meopta Admira 16
    Bach Auricon
    Cine Elmo 16
    Cinklox
    Dimaphot
    Ikonoskop
    and many more


PostPosted: Sat Oct 16, 2021 4:57 pm    Post subject: Reply with quote
screwunscrew wrote:
If I may suggest something, get yourself a ciné camera that is made for C-mount optics. Much more joy.


More joy for you perhaps, but I for one don't shoot video/movies & find c-mount lenses great for my smaller format digital cameras (as indeed some d-mounts etc. lenses are on the pentax Q).


PostPosted: Sat Oct 16, 2021 5:47 pm    Post subject: Reply with quote
not all c mount lenses have the same back focus, particularly cctv and process lenses. Make sure that they are cine camera lenses


PostPosted: Thu Feb 03, 2022 12:12 pm    Post subject: Reply with quote
I have quite a few C-mount lenses and have never seen one that did not fit into the recessed C-mount to Sony E adapters that I have. Don't forget that a very fat C-mount barrel would interfere with many 16mm camera bodies, so they are all (in my experience) "slimmed down" at the actual mount, even if they are adapted lenses for larger formats made for C-mount cameras.


PostPosted: Thu Feb 03, 2022 2:17 pm    Post subject: Reply with quote
philslizzy wrote:
not all c mount lenses have the same back focus, particularly cctv and process lenses. Make sure that they are cine camera lenses


There are CS mount lenses which I've seen miss sold as c-mount. These have 5mm less back focus. With the exception of cs-mounts the differences have all been quite small & easily corrected with a shim.


PostPosted: Tue Feb 15, 2022 1:52 pm    Post subject: Reply with quote
kymarto wrote:
I have quite a few C-mount lenses and have never seen one that did not fit into the recessed C-mount to Sony E adapters that I have. Don't forget that a very fat C-mount barrel would interfere with many 16mm camera bodies, so they are all (in my experience) "slimmed down" at the actual mount, even if they are adapted lenses for larger formats made for C-mount cameras.



In that case you are lucky. My C-mount to Sony E adapters vary in how wide a lens barrel they can accept, from around 37 to 42mm maximum. I own a fair number of C-mount lenses with barrels just over 40mm in width, CZJ Tevidons and Linos MeVis-C lenses for instance. These only fit the widest of my adapters. If you want to be sure of getting the widest C/E adapter, there are C/E adapters that also have an M42 thread (not at the correct M42 register distance of course):

Click here to see on Ebay.de

I don't own this exact model so I can't speak of its quality. Such adapters also make a useful flat base for DIY Sony E adapters.

I don't have any M4/3 gear, but such combined C/M42 adapters do seem to exist:

Click here to see on Ebay.de


PostPosted: Tue Jun 07, 2022 3:04 pm    Post subject: Reply with quote
Thanks for the suggestion. I was looking for your post for so long and I am glad I found your post.

Last edited by AlixColvin on Tue Sep 13, 2022 6:43 pm; edited 2 times in total


PostPosted: Tue Jun 07, 2022 4:15 pm    Post subject: Reply with quote
dickb wrote:
kymarto wrote:
I have quite a few C-mount lenses and have never seen one that did not fit into the recessed C-mount to Sony E adapters that I have. Don't forget that a very fat C-mount barrel would interfere with many 16mm camera bodies, so they are all (in my experience) "slimmed down" at the actual mount, even if they are adapted lenses for larger formats made for C-mount cameras.



In that case you are lucky. My C-mount to Sony E adapters vary in how wide a lens barrel they can accept, from around 37 to 42mm maximum. I own a fair number of C-mount lenses with barrels just over 40mm in width, CZJ Tevidons and Linos MeVis-C lenses for instance. These only fit the widest of my adapters. If you want to be sure of getting the widest C/E adapter, there are C/E adapters that also have an M42 thread (not at the correct M42 register distance of course):

Click here to see on Ebay.de

I don't own this exact model so I can't speak of its quality. Such adapters also make a useful flat base for DIY Sony E adapters.

I don't have any M4/3 gear, but such combined C/M42 adapters do seem to exist:

Click here to see on Ebay.de


Yes, you are right. The lenses in question are not so much cine, but machine lenses, and they sometimes have rear barrels that are wider than the C mount adapter. I have some Schneider lenses, and so far have never seen one that has a wider rear barrel than the recessed part of the C-mount adapter. Most cine lenses of which I am aware have relatively restricted rear barrel diameters, because they had to fit on turrets next to each other.
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