- A tool to drill a receiving hole
- I use a regular portable Dremel drill bit set bought from Walmart around $40 in Christmas.
- An altered M42 adapter with spring plate removed
- Tape to shield lens opening to guard against debris
- A guide for finding position to drill a receiving hole for locking pin from K mount body -- I use crayon in my first attempt. I learn it from others that any inexpensive lens or 2x teleconverter can serve as a guide in dismounting the base plate so that locking pin position can be marked on an M42 lens
Step 1: Altered M42 adapter
Alter a M42 to K mount adapter such as the Bower adapter to remove the spring plate on the adapter so that the M42 adapter can be mounted threading the screw into the lens as shown in picture below. I retain the spring plate and tiny screw for future use in a zip-lock bag
Original Kalimar 80-200 f/3.9
with Bower M42 adapter mounted
M42 adapter has spring plate removed
Step 2: Precaution & Preparation
- Tape up the rear end to avoid dust and debris in drilling
- Find a place with flat surface and I use a moist towel as a base
- Wear safety mask and gargle
Step 3: Position to drill
Here comes the part that can be replaced with a lens/teleconverter mounting plate for marking the drilling position.
I use a unused camera body, a Pentax P5 that has the locking pin as shown in picture
I use crayon pen to color locking pin to locate pin location for drilling. Lumbar crayon is preferred but my kids' crayon is right next to me and hence the shortcut for the fastest route. I push the locking pin inward and fill in with excess crayon on pin's tip. 
I then mount the M42 lens with the M42 adapter onto the K body with locking pin color coded with excess crayon. While mounting, I push the K mount locking release and released the pin only towards the last inch of mounting leaving a trace of crayon on the base plate of the M42 lens. Upon dismounting the M42 lens, I trace back the crayon to see the ending position of the crayon mark as the place for drilling. I performed few times of tracing to be sure as the crayon is easily removable and a sharp cutter can help to identity the marking.A converted K mount with a not-so-good-looking receiving hole
The receiving hole actually works but the mounting and dismounting is not as smooth as a regular K mount and the drilled hole does secure the pin in place preventing the lens to fall or dismount in abrupt turning. With refinement, it will work great.
Precautions:
- Only M42 lens with a large base can be converted
- Use all precautions in your drilling.
- For small and lightweight lens, I won't consider this conversion as small lens is good enough to be mounted with an altered adapter directly onto to the K mount. For some, the base is large enough and the locking pin from K body would give enough friction to hold the lens in place.
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