Looking for swirly bokeh on your M4/3 camera preferably at low-cost? So far you have been out of luck with native lenses and adapted full frame lenses get cropped too much to see the swirl. I have found your solution: the Computar 1.3/25mm C-mount lens. Seeing is believing, so check out the video for image and video samples!
C-mount was made for smaller 16mm film cameras back in the days and is used today for 2/3″ or 1″ sensors. This particular Japanese Computar lens is made for 1″ digital sensors and is capable of covering most of the larger 4/3″ sensor with small vignetting in some circumstances. I got this lens used from eBay for 25€.
The flange distance for C-Mount is 17.53mm and thus slightly shorter than M4/3 at 19.25mm or Fuji-X at 17.7mm. That means you are not getting perfect infinity focus unless the adapter is intruding into the M4/3 camera and I could not find such an adapter. However, closing the aperture and thus increasing the depth of field gave me quite sharp looking images for distant objects. Flat adapters to M4/3 or Fuji-X can be found for few coins from China.
The lens is tiny even by M4/3 standards with an all-metal body that feels compact and sturdy. Is is manual focus and manual aperture with two metal rings for control. Having only three aperture blades seems pretty unique to me, but I could not see any distinctive triangular bokeh shapes in my images.
We are using an Olympus E-PL5 (M4/3) with a 16 MP sensor. I am not sure how to convert the 25mm focal length exactly, but this lens felt like a fast 50mm to me.
Check out my Flickr set with this lens for full images. So what about resolution, contrast, colors and ergonomics? Well, overall performance is surprisingly interesting from a creative standpoint. Take a closer look at the following sample images (unedited jpgs).
Resolution is good enough for my taste at F1.3 in particular towards the center and getting very good towards F8. More importantly colors and contrast feel punchy when used in bright light and restrained in low light. Images do have a specific look to them that you won’t find with native lenses. Of course having such a fast lens should not be wasted on flat images of landscapes, so be creative with this one.
Bokeh can be swirly or smooth depending on the circumstances as you can see in the next image. One more trick: if you unscrew the lens slightly, you’ll get a macro-extender effect for close-ups.
Focus and aperture are manual and both rings run smooth, but ergonomics can be fiddly with such a small lens. Working with a manual lens can be a challenge as well, if you are used to modern autofocus lenses.
In summary: this lens is a small metal gem with good resolution and interesting bokeh at a low price. Think of it more as a creative lens rather than an accurate instrument, you already have a kit lens for that. If you buy one of the C-mount lenses out there, be sure that they explicitly cover 1″ sensors. Professional alternatives like the Panasonic 1.4/25mm or Sigma 1.4/30mm will cost you between 300-600$.
Thanks for reading! You can check out more of this blog or my YouTube channel.