At work we’ve been using lenses from Hong Kong’s SLR Magic. They are working out well for video applications where smooth manual control and a little “character” are more important than sharpness. This page collects my notes about working on these 12mm lenses. I have another page dedicated to the 25mm variant.
NOTE: I’m not a professional lens tech. Proceed at your own risk! If you have feedback, let me know.
The 12mm Micro Four Thirds (MFT) lens comes in several flavors as far as I can tell:
- Old style (hour-glass shaped, F1.6, focuses in the “backwards” Nikon direction)
- Original CINE version (hour-glass shaped, T1.6, says CINE on the front, focuses in the “normal” Canon direction)
This is the lens shown on this page.
- 2013+ CINE version (optics identical to the original CINE version, but with a cylindrical body and built-in lens gears)
These lenses are flare-prone and unsharp wide-open, but great at middle apertures, compact, and well-built. We also use manual focus Nikkor primes, but they’re bigger and require MFT adapters and de-clicked aperture mods. They’re also not available in 12mm!
Adjusting Infinity Focus
If you can’t achieve sharp focus on distant objects when the focus ring is set to infinity, you need to adjust the focus ring (somewhat similar to the “back-focus adjustment” on zoom lenses).
The focus ring has 3 tiny set-screws around it’s circumference, and 1 bigger screw. Loosen and immediately re-tighten each tiny screw individually to make them easier to handle later on. (This is just to break any threadlocker.) Don’t do all three at once because we don’t want to decouple the ring from the focus mechanism yet!
Mount the lens on a camera. Rotate the lens ring to infinity and remove the big screw. (This screw hits preset stops inside the lens, to prevent the ring from turning 360 degrees.)
Now that it’s gone you can turn past infinity! Point the camera out a window and focus on a very distant object.
For critical focus, use a wide aperture and the camera’s digital magnification. (ND or a fast shutter speed might be required.)
Without turning the focus ring, loosen all 3 tiny screws. Now the ring should be very loose because it’s decoupled from the internal focusing mechanism.
Rotate the focus ring until it’s within the normal range (infinity or closer) and replace the big screw.
Rotate the focus ring exactly to infinity and tighten the 3 tiny screws. Your lens is now fixed!
Disassembly and Re-assembly
It’s hard to find repair info for these lenses (and expensive to send them to HK). The videos above (not mine) are enormously helpful. As shown in the videos, mark the positions of the pieces before you take it apart! They need to be aligned again for re-assembly.
Disassembly (see “loose bajonet” video)
- Prep the lens base by making sure the focus ring is in the right position relative to the lens mount. (You marked it, right?) We’re assuming that the focus ring is locked to the the helicoid but the larger end-stop screw is removed.
- Hold the lens base components together (so the mount and focus ring don’t change their relative position). Spin the lens body into place until it binds. (Helicoid threads will be showing.)
- Back off a bit and line up the lens mount’s red dot with the center indicator on the lens body.
- Change your grip: Now hold the lens mount and lens body so they don’t spin relative to eachother. Turn the focus ring to bring them together. Wiggle the mount at first to make sure the centering pin is finding the groove inside.
- Once the lens body bottoms-out, spin the focus ring the other way until the rear element of the lens is flush with the back of the lens mount. (This should be near the “close” limit of the focus ring.)
- Put the large end-stop screw back in the focus ring and test for infinity focus.
The Lens Base has 3 parts:
- Micro 4/3 Lens mount (including groove for brass centering pin and hidden end-stops to limit travel of focus ring)
- Aluminum focus helicoid
- Focus ring (with 3 tiny screws that grip the helicoid and 1 larger screw that hits the end-stops in the lens mount)
The lens body has a brass pin that rides in the centering groove of the lens base. On our lens, the brass pin has a filed-down “flat” on the side (click for fullsize pic) to make it fit better in the groove. Make sure it’s oriented properly or else focus will bind!
(I used threadlocker to set the position after I fixed the orientation.)