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.
The main issue is that unless relatively recently made, there will be no documentation for the essential information about the lens.
C Mounts were invented in the 1920s or 30s by Bell & Howell, USA. They superceded the A and B mounts and if the cine lens is very old you may find it has registration issues because these mounts do not have the C mount back focus distance, also known as registration distance.
200 line pairs per mm are possible with Kowa c mount lenses. Too sharp really, but that is why they invented mist filters. These lenses are generally very small, but some can be larger than the FF, 135 film format equivalent, for technical reasons.
They are very easy if older, to CLA, Clean Lubricate and Adjust.
The Chinese are making some very interesting C mounts some that are better than others.
Some C mount lenses can cover APS, ie the have an image circle of 33mm or more. Some are now converted to Leica M mount and presumably do a decent job of covering the FF sensor. They go for $2,000 or more. The best are Fench, English or German. The USSR neglected C mounts and have a 27mm mount that looks similar to the C mount but the Czechs made some decent Zeiss copies. The best cheap lenses are Japanese, made for TV. The 0.7 25mm the 0.85 50mm Canons, etc were the peak at the time and give the lie to cheap TV lenses! Some hyperfasts will not suit m4/3 but do fit the Digital Bolex, the D16.
The main problem is that the sellers do not test or report on the details, and some unscrupulous ones charge a lot for very little.
There are difficulties in setting some c mounts into the adapter. It is a bit of a minefield. Despite this, prices have jumped a lot.
Unless you know what you are doing, do not pay more than $100 for any C mount. If starting off, buy locally testing first or else stick to the cheap Chinese lenses. They can still be had for $40 or so, often with adapters. Some will say they are for 2/3 sensors, 1/4 the area of m4/3, but infact they may cover APS.
The small form factor makes for easier disguise or for use as a crash cam or drawer safe camera showing a face as talent opens the door etc.