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Lomo/Lenkinap KSK mount lens modifications and adapter
  • This is an ongoing thread, I'll include pics and descriptions as I go.

    So in the other thread about using Lomo lenses, I decided to try going back to using Russian glass. I found some interesting "Lomo" lenses but it turns out they are in a rare mounting called KSK/KCK. This apparently was used in only a model or two of camera. The actual lens modules are the same Lomo modules that all of the other 35mm lenses use but the mounts are made by someone else. The mounts are bayonet like the BNCR/PL lenses are but are a different diameter and much longer, which means the FFD is a few mm too far away from being usable as-is. It was obvious that I needed to modify the lenses to get the rear of the lens closer to the sensor. I also needed to make an adapter for the KSK flange to the M4/3 mount.

    I'll try to include as much info as possible (such as the drawings/measurements I made) but be warned, the modifications needed to make the lenses work are not easy and cannot be done without access to precision tools. Also needed is a lot of patience and many years of practice machining different metals. So far I've spent 40$ on the adapter parts but have spent probably 20 hours machining it and the lenses. If I still had access to the machine shop I used to work in, it would have taken me a lot less time using a multi-axis mill. Unless someone figures out a better way to modify the lenses, simply making an adapter will not work.

    image

    image

    KSK mount: 60mm diameter, 40mm flange depth. Unknown Flange Focal Distance (estimated to be around 55mm which is 5 mm too far away for M4/3 flanges)

    Adapter: I started by looking at adapters already on the market to see if there was anything I could purchase and modify. Most of the adapters out there are OUTRAGEOUSLY priced for what they are. I couldn't justify spending hundreds of dollars on something I didn't even know would work. I decided to machine my own. I started by buying a piece of 3"OD/2"ID 6061 aluminum round pipe and a C-mount to M4/3 adapter. I cut the C-mount adapter down to 2.010"OD to press fit into the 2" pipe. This eliminated the need to machine the M4/3 mount. I started out cutting a 40mm section of pipe for the adapter body and cutting a 15mm section for the retaining ring. I used a lathe to open the ID of the pipe to 60mm for most of the length while leaving a 10mm section where I could press fit the M4/3 adapter. I then machined down the OD of the pipe to 70mm to match the OD of the KSK mount. I machined a notch for the retaining ring's retaining screws to rotate in. While there was some machining done to enhance the fit of the adapter, it was pretty easy to make. The hardest part was finding the right balance between adapter length and lens modification.

    Retaining ring: I machined the ID of the retaining ring to match the adapter body while leaving a lip to hold the bayonet ears. I scribed the outline of the KSK mount and used a saw and rotary file to cut the notches for the ears. I drilled and tapped a few holes for retaining screws. I used the rotary tool to angle the ring's retaining fingers so that when turned, would tighten against the flange.

    image

    Lens modification: So the flange body needs to be shortened but the pin that keeps the focus body from turning is located at the back of the lens:

    Before:

    image

    After:

    image

    This means that the focus body needs to be shortened as well to move the focus pin towards the front for more clearance for the adapter. First I cut down the flange to the point where I could gauge the FFD using the actual lens and camera. I would need to machine ~8mm from the flange and focus body to clear the internals of the adapter while moving the rear of the lens back far enough to focus.

    The KSK mount is held to the outer focus housing with a large threaded ring. The ring would need to be moved to get the focus range we need. Since I don't have the machines needed to make a fine pitch metric thread, I decided to machine a groove and use a retaining clip (also called a snap ring). I picked one out that had the right OD to fit and then machined the groove in which it would sit. I then machined back the KSK mount to the point where the ring would hold it tight without play.

    image

    I then took a thin piece of the KSK mount that I had cut off and welded it back onto the mount. I filed this down to 5mm width and machined a 1mm thick steel plate to guide the focus mechanism. This reduced the mount depth from 40mm to something like 30mm which ultimately gave me 1mm of clearance in the mount.

    image

    I've done 2 lenses already and I'm currently finishing up the modification to 2 more lenses. I'll also be making a second version of adapter, hopefully making it a little nicer and tighter fit. I'm also trying acetal plastic for the focus guide plate instead of steel to see if I can get it tighter without dragging.

    The actual lenses are really nice. I think they are sharper than my Nikons and when set up properly I also get more focus range and a lot less breathing while due to the precision helicals. I also switched to a boron based grease which is the smoothest grease I have ever used in a lens.

    What is strange is that the focus marks are off in range. If I get something in focus at 10ft and then focus at something 3ft away, the focus mark shows 1.5ft. This is the same as my set of Nikons which makes me believe that it's a function of using a 35mm lens on M4/3 sensors.

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