Today, the sun came out, after two days of rain, so I decided to test a 25mm C-Mount CCTV Lens on an Olympus OMD-EM5.
The “C” in c-mount stands for cine, as that was their original application. C-mounts are screw mount lens and used on 16mm movie camera and closed circuit TV cameras. They come in a range of sizes and many of them can be attached to other cameras via an adapter. They are well suited for micro four thirds cameras because of their small size. While you can find expensive ones, you can also find very cheap c-mount lenses on eBay.
I have two of them: A 25mm/f1.4 and a 35mm/f1.7. Since the OMD-EM5 has decent video capability, I decided to shoot some video with the 25mm. There are a few challenges involved. First, the 25mm has no click stops, as you change apertures. Also, it has no f-stop markings on the lens barrel. (the 35mm has no click stops, but does have f-stop markings.) You just have to look through the lens and see if your scene is getting lighter or darker to know if you are opening the aperture, or stopping down. It’s not a huge problem, but it does make setting an exact exposure somewhat interesting! To solve the problem, I guessed at the exposure, made a still photo and looked at it on the LCD. Luckily, I got a usable exposure but felt it was a little too bright, so I introduced a .7 negative exposure, shot again, and nailed it. I could have just used manual and entered the aperture and shutter speed, but decided to set the EM-5 to aperture priority. Since it was a bright day, I wasn’t concerned about shutter speed.
Micro four thirds sensors are smaller than 35mm film frames and have a x2 crop factor. Hence, the 25mm lens is, effectively, a 50mm. The 35mm is a 70mm 35mm equivalent.
This is what I got, at ISO 200, and 1/2500.
The two c-mount lenses that I have seem to be made of high quality materials, but are manufactured to loose tolerances, so they feel cheap. Also, the focus and aperture rings are very small. The focus ring is very close to the camera body, and very difficult to adjust smoothly. Well, for the $30 that I paid for each lens, including the adapter, I really can’t complain. I wasn’t expecting a technically advanced lens. If you can live with some softness, vignetting, and other flaws, they are fun lenses to use and could give Lomo/Holga type results to some of your video projects.