Lens Hacking Made Easy: Praktica M60 26mm f/5.6 to Leica Thread Mount
Time for another edition of Lens Hacking Made Easy. Our subject this time is a basic one, the 26mm f/5.6 lens originally installed in the Praktica M60, a very simple consumer point-and-shoot. What makes it a good choice for hacking into a Leica Thread Mount? Well, at 26mm it’s quite wide, which is a bit unusual, and as the manufacturer noted it’s a “Glass Lens,” three elements in three groups in fact. I’ll grant you, that’s not the most compelling argument, but it’s a start.
What really makes this project appealing is that the finished product would be incredibly small. Part of the inspiration were the MS Optical series of Perar Super-Triplets, tiny limited production lenses that are not much bigger than body caps; while I had no delusions that this lens would come anywhere close to the quality of the MS Optical unit, and certainly would not have the same flexibility, it could at least be just as compact.
As an extra bonus, the simplicity of the donor camera makes the conversion particularly easy. You see, the M60 is a fixed-focus camera, so there’s no need to covert the focusing mechanism over into the new mount. Being such a wide lens, it was simple to set a hyperfocal distance of 4m, which means that everything from 2m to infinity should be in focus.
What about at wide apertures, you ask? Not a problem, as the M60 lens is an f/5.6. I wasn’t able to find any information from the manufacturer about this, but I have a suspicion that it was in fact a fixed aperture as well. Whether it was or not, I decided to simply build it as a fixed f/5.6 lens with no aperture mechanism at all. If used with film you need to be a bit careful about matching film to lighting conditions, but other than that it works just fine; with digital of course it’s even easier to manage by adjusting ISO.
So essentially what we’re looking at here is simply building a solid mount for a very small piece of glass that puts it at the correct distance from the film plane. It’s not a particularly complicated task.
The starting point is a Leica Thread Mount body cap, easily and cheaply available on ebay for a few dollars. All that needs to be done is to drill a hole of the appropriate size, then devise a way to mount the lens at the correct depth. Drilling the hole was accomplished with the help of a purpose-built jig to hold the body cap in place. I used stepped drill bits, which have the added advantage of being self-chamfering, leaving a nice clean edge on the hole.
Once the hole was drilled, it was time to mount the lens. Whenever possible, I prefer to use readily available materials. In this case, I chose some metric copper washers I had on my workbench. The holes fit the lens perfectly. I kept the basic mount from the M60, a simple plate into which the lens unit threads. This allowed easy fine tuning of the lens position via the fine threads, as well as providing a stable plate to rest on the washer stack. I determined that I needed four washers to get the proper depth, so I epoxied them together, then epoxied the stack to the back of the body cap.
Once the epoxy was dry, it was a simple matter of temporarily placing the lens in the mount and fine-tuning the focus. My Fuji X-E1 was pressed into duty for the task. A few tweaks and I had things dialed in. Once everything was finalized, I masked off the face of the assembly and painted the back surfaces and the lens recess flat black. After the paint dried I placed the lens into the mount and secured it with a couple drops of white glue; I prefer this for such applications, as it’s easily removed if something goes wrong, but it’s strong enough for non-load-bearing applications and will not adversely affect any types of materials.
Basic testing was done with the Fuji for convenience, but the real test was going to be on film. I already knew there would be some compromises. A quick check of images online showed that the M60 tended to vignette a fair bit, so I figured that would carry over into my conversion, perhaps even moreso, as the lens ended up quite deep in the mount. I had no illusions about image quality either – this was a basic consumer point-and-shoot probably made (as far as I can tell – there were no markings on the camera) in the waning days of East Germany (EDIT: a sharp-eyed reader over at APUG noted that the Praktica M60 bore considerable resemblance to a Fujifilm Clearshot S, and after a quick check around the interweb I’m inclined to agree, so my previous speculation about its origins were quite incorrect) ; I was not expecting much in the way of sharpness and fine detail, especially out toward the corners, where distortion was bound to be fairly pronounced. I screwed it onto one of the Leica IIIcs and loaded up a short roll of FP4+ to see just what I was dealing with.
You can make your own judgments from the photos (I suggest clicking for a larger view), but all things considered, it exceeded my expectations. I expected the vignetting to be a lot worse. Center sharpness isn’t too bad, and the softness in the corners is limited to the farthest recesses. There’s some distortion, both the expected distortion of perspective of a wide angle lens and some due to the aberrations in the lens, but it’s not so pronounced as to distract from the overall image. Contrast is pretty good, probably aided by the fact that the depth of the new mount acts as a substantial lens hood.
Using it is almost too easy. Mounted on a fully manual camera, I had to resist the automatic reflex to check the lens settings before shooting. While I do have an appropriate external viewfinder, I decided to see how shooting without it worked. Framing obviously involved some guesswork, but with a lens this wide it’s hard to miss too badly; the second shot was taken from the hip without framing at all. It really does turn the camera into a very small point-and-shoot.
So there it is, another slightly misguided, perhaps rather pointless lens hacking project brought to completion. It’s not as if I needed to do this, but somehow the challenge of doing it was appealing. I haven’t tried it with color film yet, so I’m not sure what to expect there, but with black-and-white it’s good enough to play with. It’s a nice oddball to throw on the camera every now and again when the mood strikes, and the compactness of it does make it awfully handy.
