Holmium V2
I finished the second version of the Holmium camera in early 2020, the camera was redesigned centering around the 50mm f/2.8 Bronica ETR lens this time. The rangefinder was improved to be a combined rangefinder-viewfinder, for a better shooting experience. It uses a rotating cylinder setup. The baselength is 75mm, with a 0.42x viewfinder (50mm on 6x7 is quite wide). All of these factors combine to make quite a large rangefinder, which is convenient as it’s quite a lot easier to work.
There were still a lot of issues with the design however, small MJF parts are quite flexible and so they were not reliable. My design for the front surface mirror post was also not great and quite unreliable, it was deformed when it arrived and so adjusting it with the built in calibration way almost impossible. I had to resort to shims to get it sitting correctly. Overall It was more enjoyable to use than the previous version but not by a whole lot. V3 is already in the works, and does away with the rotating cylinders in favour of rotating the second PCV lens.
The focusing group was also redesigned, borrowing the design used for the Carbon. It uses micro-bearings, cams and cam followers, in a similar fashion to what some cinema lenses would, albeit cutting some corners to keep the budget in line, since I’m not producing these in any sizeable quantity, part count is more of a issue.
This second attempt felt smoother than the one on the Carbon, the tolerances were better, and I derived the formula to compensate for cam steepness, so that the follower wouldn’t get pinched. Something that was an issue on the C mainly because it employed a variable pitch cam.
The V2 also got an improvement in the counter department. it now has reliable frame spacing, due to a mechanical counter, based on a combination of the Hasselblad design, and an old Plaubel roll film back. The counter uses a 1:16 total reduction down from the main advance spool, and thus maps out the frame around the final ‘counter gear’. There a pawl ratchets into slots which are spaced correctly for 10 shots on a 6x7 roll. This design has the benefits of being highly adaptable, as it could easily be modified for different formats. the main drawback being that it’s still quite manual, you have to unhook the pawl before advancing the next frame, and you have to set it back manually. The latter issue only needs a return spring, and coupling to the back door being closed to be fixed. The former would need linking from the advance to the shutter release, which is slightly more work.
