C mount adapter Compatibility

Philip Kral · January 17, 2012

Hi everyone! It's been awhile, I've had a little accessory issue I was hoping someone here could help me with. Recently I've tried to adapt some of my 35mm Lenses to my 16mm cameras. (Yes I know there's a change in focal length/ crop issue when you do this.) The C mount adapter that I have recently stumbled upon does not fit entirely into my camera. The first thread or two does but then it doesn't go any farther, it doesn't fit any of my other C mount cameras either. I know that some of the video C mount cameras have slightly different threading so i'm assuming that's the core of the issue- It's probably a C mount video and not a C mount 16mm. Does anyone know how to resolve this issue? Is the difference with the thread pitch or is there some way I can modify it? How can I make sure which C mount adapter is which if I try to get another one?

Charles MacDonald · January 18, 2012

http://en.wikipedia.org/wiki/C-mount sums it up.

perhaps your adaptor is not a c-mount?

Charles MacDonald · January 18, 2012

should go farther I guess.

If the adaptor does not fit several c-mount devices, and if it only goes in a few threads is it not a c-mount.

Also THERE IS NO CONVERSION OF FOCAL LENGTH when you move a lens to a different type of Camera. A 50mm lens for a 35mm movie camera will be 50mm on a 16mm camera, a Video Camera, a 35mm SLR, a Digital SLR, or an Instamatic. This whole business seems to have gotten started with the small sensor Digital Camera with the lens marked as "equivalent focal length" so that a 13mm lens on a teeny sensor acts like the equivalent of a 50mm lens on a 35mm SLR.

If you have a 50mm lens and put it on a 16mm camera it will work like any other (slight telephoto) 50mm lens on the 16mm camera.

Philip Kral · January 18, 2012

should go farther I guess.

If the adaptor does not fit several c-mount devices, and if it only goes in a few threads is it not a c-mount.

Also THERE IS NO CONVERSION OF FOCAL LENGTH when you move a lens to a different type of Camera. A 50mm lens for a 35mm movie camera will be 50mm on a 16mm camera, a Video Camera, a 35mm SLR, a Digital SLR, or an Instamatic. This whole business seems to have gotten started with the small sensor Digital Camera with the lens marked as "equivalent focal length" so that a 13mm lens on a teeny sensor acts like the equivalent of a 50mm lens on a 35mm SLR.

If you have a 50mm lens and put it on a 16mm camera it will work like any other (slight telephoto) 50mm lens on the 16mm camera.

I dunno, as the wikipedia article says there seems to be different variants (Such as that CS mount one- although it states it should fit.) Regardless, I remember other people having this issue and the box and the adapter is indeed marked "C mount"

Are you sure there is not a crop factor? I asked this question before and people told me that the crop factor kicks in when you use a smaller gauge. But I'm sure you are correct about the digital side of things, my T2i and the 7D have a crop factor of 1.6x when you try to use 35mm lenses. I thought it would have been strange for that to translate to the film side of things but many S16 cameraman have sworn by it.

Needless to say, this has only made me slightly more confused. What the heck kind of adapter do I have then?, lol. The company doesn't seem to respond to my E-mails, I fear they think I'm just some idiot who doesn't know how to use a C mount lens.

Chris Millar · January 18, 2012

I think keeping to focal lengths as focal lengths makes sense.

How on earth would these crop factors account for aspect changes ? You'd have two crop factors ...

As for the c-mount - hmmm, have you given the common factor a close inspection, it's not damaged ?

Charles MacDonald · January 18, 2012

Are you sure there is not a crop factor? I asked this question before and people told me that the crop factor kicks in when you use a smaller gauge. But I'm sure you are correct about the digital side of things, my T2i and the 7D have a crop factor of 1.6x when you try to use 35mm lenses.

yes, I have an Conon Xti, with a "small" (APS-C) size sensor. it takes part of the image out of the center of the lens, so I have to use a different Focal length than if I use a film Camera or a Full Digital to get the same part of the subject in the image shooting form the same spot. In that regard the XTi came with a 17- 50mm lens while the film camera uses a 28-70 so they both have about the same range. BUT I can put say a 200mm lens on the XTi and that lens is still 200mm, and the camera will list it as 200mm on the metadata. To get the same shot with the film camera I would have to use a slightly longer lens. If I put a 200 mm lens on my Filmo with a c-mount adaptor, it will still give me a similar image to a 8 inch 16mm camera lens. (8 Inches at 25.4 mm is 203.4mm)

Philip Kral · January 18, 2012

yes, I have an Conon Xti, with a "small" (APS-C) size sensor. it takes part of the image out of the center of the lens, so I have to use a different Focal length than if I use a film Camera or a Full Digital to get the same part of the subject in the image shooting form the same spot. In that regard the XTi came with a 17- 50mm lens while the film camera uses a 28-70 so they both have about the same range. BUT I can put say a 200mm lens on the XTi and that lens is still 200mm, and the camera will list it as 200mm on the metadata. To get the same shot with the film camera I would have to use a slightly longer lens. If I put a 200 mm lens on my Filmo with a c-mount adaptor, it will still give me a similar image to a 8 inch 16mm camera lens. (8 Inches at 25.4 mm is 203.4mm)

Ah, I see where the confusion came from. Interesting how the characteristics change from one format to the other. Thank you. As for the adaptor, it's not damaged. I'm wondering if mabye there's a coating of protective paint on it that's too thick or something. By eye it looks like the same threads as my other c mount lenses, but I need some way to measure the pitch and size of the threads to be sure.