Reading
this thread gave me the impetus to code my lenses using a Dremel this afternoon.
Total success - and my lenses didn't end up looking like a dog had chewed them. either! So, thanks for your post, Tom.
I practised on a bit of scrap brass, and, like Tom, found that a spherical engraving bit worked best - it was easy, with a bit of care, to create oval pits with a nice regular shape. The spherical bits did not create any burrs, though I did run a piece of 1200-grade wet-and-dry paper gently over the pits, to take off any sharp edges.
After practising, I found the best technique for me was to draw lines accurate lines where the pits are to go, using a fine indelible marker. I then set the Dremel to its lowest speed (setting 1), and ground shallow indentations at the start and end of each line, marking the ends of each pit. I then connected the pits, holding the Dremel steady but without too much pressure - pressing too hard made the Dremel more likely to slip, and not much pressure is needed to grind brass anyway.
I used the smallest bit (0.8 mm ball diameter) initially, and the resulting pits were about 1 mm wide.
After a few dummy runs on the scrap brass, I was ready to attack a lens. I decided to do my Voigtlander 25 mm lens, since it cost a lot less than my other lenses!
I've got Tim Isaac's
M-Coder Kit, so marking the pit positions was a breeze. After masking off the rear of the lens with masking tape and paper, to keep out swarf, with trepidation I then started grinding... All went well, and, feeling pleased, I filled in the pits with Humbrol matt paint (as used for Airfix models), using the
Leica lens code table for the lens codes. I chose this paint as it's easy to clean off with common solvents like lighter fluid or white spirit.
Then I took a photo: lens not recognised!
I Googled, to look at lens coded by Leica, and decided the problem was that the pits were too narrow. Back to the scrap brass for more tests. I used the 1.6 mm diameter spherical bit, mainly because that was all I had. It was perfect: gently running it up and down the existing 1 mm pits enlarged the pits in a well-controlled manner. I did try cutting pits from scratch with the 1.6 mm bit, but the bit was harder to control, and the pits looked a bit ragged. So, using the 0.8 mm bit followed by the 1.6 mm bit gave the best results: the 1.6 mm bit was easier to control, and created pits with nice regular edges.
I repainted the pits, and took another photo: it works!
Flush with success, I engraved pits in my Leica lenses (and, yes, I was nervous!), and an hour later, all my lenses were neatly coded, and recognised by my M8.
I'm attaching a photo of my Summilux 35 mm pre-aspherical lens. The pits aren't totally identical, since I'm not a machine, although some of the irregularities you can see are actually from careless painting of the pits - I was in a rush to try out the lens, so just slapped the paint in (I'll repaint it later)! Personally, I think it looks pretty damn tidy, even if I say so myself!
[As an aside, the shroud protecting the rear element fouled the M8 lens throat, preventing the lens being focused at infinity: to fix this, part of the shroud has been removed (the portion at "five to four", if you imagine a clock face). The portion removed was 1 mm deep and 7 mm inwards from the shroud edge. Also, I'm using a Summicron hood (with a hole cut in one corner for the viewfinder), as the original round one is hopeless at preventing flare.]