I keep hearing things about using CCTV C Mounts hacked into a Micro 4/3 camera using an adapter. Does anybody have any experience with this? Can any ebay lens work, or is the C-mount not universal? Can you really take video with virtually no lighting?
C mount is universal, CS is the same mecahnical thread but a shorter back focal distance.
C mount CCTV lenses are normally very short focal lengths, they are made for wide angle with TV cameras that have very small imagers = very large crop factors.
They are also generally poor optical quality - CCTV doesn't demand Ansel Adams levels of sharpness.
So it's not clear why you would want to use them on an expensive micro 4/3 camera
The C mount may be universal, but they are made for a number of different sensor/film sizes. This means many will not cover the entire 4/3 sensor. This will result in vignetting or a dark circle, requiring cropping of the final result.
A C mount lens designed for a smaller image circle than 4/3 (such as, one for a 1" tube) may still cover the entire 4/3 sensor adequately, although this can depend on lens design and focal length - the longer focal lengths often have less vignetting.
So it pays to do a search on the various micro four thirds forums and see who else has experience using a particular lens on their micro 4/3 system. I can't speak for its completeness or accuracy, but a glimpse at Wikipedia turns up this list of C mount lenses: http://us.c-mount.passion.pro/
Another thing to consider is that the flange to focal plane distance of C-mount is a bit less than that of micro four thirds, which means that the back of the lenses will protrude back into the camera body a few millimeters. This is not a problem usually, as micro 4/3 has no flip down mirror, but it does have some other delicate equipment and you should still exercise care. It's not unknown for some C-mount lenses to need some protruding parts ground off their rear end to be able to fit safely.
I've seen some beautiful effects as a result of using one of these lenses on a micro 4/3rds camera body.
Interesting experiments to be made, I think.
I use a Pentax 25mm c-mount lens on my Olympus E-PL1 with no problems at all. It actually takes beautiful pictures, although it may not be quite what you are expecting. These lenses were generally designed for smaller sensors or film formats, so will often show some vignetting (some more than others). Additionally, they often have some fairly significant distortion around the edges as well as a "swirling" bokeh that you may or may not like. Unfortunately, not just any ebay lens will work out of the box. Some of these lenses require some physical modifications to allow infinity focusing. You can get a sense for the types of images these lenses produce from this excellent 25mm c-mount vignetting shootout.
As a starter, I would recommend the same lens that I have (Pentax/Cosmicar 25mm). It is popular, widely-available, affordable, quite fast (f/1.4, although maybe closer to f/1.8 in actual performance) and requires no physical modifications. It also takes pretty darn good pictures without a terrible amount of vignetting. You will have to focus manually, of course, and you can pick up a cheap c-mount adapter on ebay.
you can see some actual video samples here https://www.youtube.com/watch?v=l5epzYrOZBA&t=398s my "rambling" is in Polish, but the onscreen descriptions show which lens was used to shoot the scene. Except for the 25mm/1.4 which has some vigneting the other two work great.