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C mount question.

Discussion in 'Adapted Lenses' started by ke7dbx, Oct 1, 2011.

  1. ke7dbx

    ke7dbx Mu-43 Regular

    May 11, 2011
    I was wondering with the size of the c mount lenses. Is it the same crop factor that you would have with full sized SLR glass? Part two. What is a good adapter. I have seen a lot for sale on eBay among others.

    Thank you.
  2. photoSmart42

    photoSmart42 Mu-43 Top Veteran

    Feb 12, 2010
    San Diego, CA
    1. Crop factor is a matter of relative sensor size and has nothing to do with lenses, so yes it would be the same crop factor (except for the fact that you can't put C-mount lenses on SLRs - the C-mount flange distance is very small, barely long enough to focus on m43 mounts)

    2. There are a number of adapters out there. The main thing to look for in C-mount lenses is the bottom diameter of each particular lens. The C-mount specification only refers to a given flange distance, and the thread size. There's no specification for the bottom of the lenses. To give you the widest assortment of lens compatibility for C-mount lenses, you'll want an adapter with the widest/thinnest possible base. I have a Kipon and it's nice. I've heard good things about Metabones.

    Good luck!
  3. RobWatson

    RobWatson Mu-43 Hall of Famer

    Actually, crop factor will depend on exactly which type of c-mount is being considered. C-mount comes in 1" format (16mm circle), 2/3", 1/2" and even several smaller image circle formats. Especially the CCTV type lenses.

    Also, due to the increasing levels of abberations as one approaches the 'edge' the evvective crop factor will vary slightly even within a given format. For example my 50mm F0.95 actually is pretty good across the full MFT sensor while my 25 and 17mm F0.95 are good for only ~1/2 the sensor and likely less when peeping at the abberations.

    I have a gallery here for the Navitar 25mm and 50mm F0.95 lenses so you can see for yourself.

    For practical purposes most c-mount in 1" format are good only for video unless you don't mind lots of cropping.

    Also, watch out for protrusions from the lens that extend out the rear beyond the mounting threads! The c-mount specification actually does not include any info about the free space requirements between image plane and mounting flange. There are many lenses with such rear protrusions and some will not even fit into c-mount cameras! I have a Kowa 8mm F1.4 c-mount lens with a modest 4 mm protrusion that will not actually fit on my E-P1 at the extreme focus settings.

    Also 2.0, some lenses are simply too large in diameter at the mounting flange to even fit into the various c-mount-MFT adapters!
  4. photoSmart42

    photoSmart42 Mu-43 Top Veteran

    Feb 12, 2010
    San Diego, CA
    Not trying to be argumentative, but crop factor and lens coverage/vignetting are different things. You're describing lens coverage. Crop factor is a relateive sensor characteristic, lens coverage/vignetting is a lens characteristic.
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