Sunday, February 8, 2015

C-Mount lenses on MFT (micro four thirds)

Micro Four Thirds was unique among interchangeable lens cameras when it was introduced. It was smaller than DSLRs, yet had a decent sized sensor - the same size as Olympus and Panasonic DSLRs at the time. Almost 70% the area of a Canon APS-C sensor it was capable of delivering very decent quality. What made it really unique was the very short "flange distance" made possible by not using a mirror as is "normal" in an SLR.

The flange distance is the distance from the sensor to the lens mount surface of the camera. Nikon F-Mount DSLRs for example have a flange distance of 46.5mm. Lenses where the rear element gets beyond this point risk being smashed by the mirror when taking a picture. Remember in a DSLR, that mirror is directing light upwards to the viewfinder, and when you press the shutter, it will swing upwards.

Micro Four Thirds uses a 19.25mm flange distance. This means that if A Nikon F-mount lens were held 27.25mm away from the Micro Four Thirds camera's mount over the sensor, it would be able to focus properly on the sensor, since it's the same distance it would be in a regular Nikon F-Mount camera.

In a case like this, adapters are made to let users mount the lens onto their Micro Four thirds cameras. Normally they are manual only, as no electric signals will get from the lens to the camera. This is fine though, as old lenses usually have the wonderful feature of an aperture ring. It's just like aperture priority in regular use, except now your aperture control is a direct mechanical link. Sounds better actually :)

C-Mount lenses refer to a range of lenses used on CCTV security cameras, 16mm movie cameras, machine vision and robotic applications etc. The problem with assessing one of these to determine if it will work on a MFT camera properly is the image circle of C-Mount is not standard. The Sensor for These can range from 8mm (also listed as 1/3") to 25mm (1"). A 1" format lens is generally more expensive, but is more likely to cover the MFT sensor. Some 2/3" format lenses can work, but generally result in vignetting, and poor quality edge/corner images.

C-Mounts are fun because they're generally tiny. After all - if you have a 25mm adapted DSLR lens, it's fairly hefty on a small MFT camera. Drop in a C-mount 25mm F1.4 and it's still tiny! Go cheap of course, and the quality wont match the DSLR lens. Indeed, most C-Mount lenses result in a picture far from perfect - however, they are cheap, fast can be capable of good center clarity, and can give off a unique swirling bokeh that when utilized is hard to match.

The Lenses:

A smattering of c-mount lenses. Clockwise from top left: General Electric 25mm F1.4, Canon PHF 35mm F1.2, Cosmicar 75mm F1.4, Wollensak 25mm F1.5, Pentax 25mm F1.4.

One of my favorites. A Wollensak 25mm F1.5. Before fast lenses were common on Micro Four Thirds, these small 25mm lenses were quite popular. This originally was meant for old film video cameras. Some vignetting, but recoverable. Lovely render!

This lens looks rather interesting, but vignettes too much at the corners. A General Electric 25mm F1.4 TV lens. Much cheaper than the Wollensak, and the image quality showed it too.

Pentax 25mm F1.4. If one were looking for better quality than the cheap c-mounts from china, this was the one to get. For about $100, this gave a more neutral picture compared to the Wollensak. Other than the extreme corners, there is less vignetting, color was more neutral, though it wasn't quite as sharp. Still a decent lens, and extremely smooth focus action.

The Cosmicar 75mm F1.4. Cosmicar was a Pentax division. I'm not sure if it was a purchase by Pentax, or if it originated from them, but Pentax is now Ricoh. Pentax was merged into Hoya and Ricoh purchased the imaging division.

Another angle showing the nice large front element. While it's large, it's not bad to handle.

This is the Canon PHF 35mm F1.2. It required heavy modding to fit on here. When I work this hard on something I generally like it more than I should. That said, I can't help but love how sharp this lens gets in the center. Face shots of my daughter are wonderful with this, and the focus plane curves forwards towards the edges - this curve makes facial features go out of focus FAST - not optimal, but it if you're wanting to blur, this will satisfy.

The adapter itself is little more than a MFT mount, on a flat washer like bit of metal, with a threaded inset. There are several makes and models available. If you're after a nice thin one to maximize adapting lenses, consider the pictures below.

Sample images:

Christmas tree light bokeh! This was shot with the canon PHF 35mm at F1.2. note the shape of the bokeh circles as the lights are positioned towards the edges and corners of the frame.

Here's a few samples from the above lenses:

The 75mm F1.4 Cosmicar delivers enough coverage and sharpness to pass mustard. While it starts off bright and decent enough at that aperture, stopping down doesn't aid it that much. That said, the bokeh is superb giving a smooth render.

The 25mm F1.5 Wollensak shows a heavier vignette that one would be used to  with standard commercial lenses. It's decently sharp in the center and resists veiling and ghosting enough to be used as an everyday lens. Size as pictured above also helps that designation. Being easy to carry has it's perks! If the best camera is the one you have with you, then being able the carry a good camera means a lot too.

Shot with the Canon PHF 35mm at F1.2 You can see the difference compared to the above Wollensak. The bokeh certainly stands out more - though in comparison to the 75mm, it's not quite as smooth. Note also the curvature of the keyboard, and the heavy vignette. This lens is extraordinarily sharp in the center wide open, yet fails miserably in the corners. This actually makes the lens quite capable of adding focus to a picture. Viewers eyes will be attracted to the sharp center. This can add an artistic element to face shots, and the curvature and character of the render does nicely with lights in dark shots.

The best place to get C-mount lenses imo is While the Pentax 25mm F1.4 was sold up until recently, it was discontinued. Lenses like the Wollensak have shot up in price to astounding levels due to their rarity. I think most legacy lenses would only have their value rise over time as better mirrorless cameras with better manual focus functions (like focus peaking) become available.

For more information on c-mount (cine) lenses, there is the cine-lenses sub-forum at with numerous threads of information and the c-mount on M4/3 group on facebook is quite lively.

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