I've been messing around with camera mods lately, specifically, modifying 35mm SLRs to shoot other formats. My first project was a half-frame Pentax MZ-3, and currently I've been enjoying a PZ-1p that I converted to shoot square frames. The conversion involves masking the film chamber and the viewfinder to the desired frame dimensions and also modifying the frame advance to pull the appropriate amount of film. This is the interesting part, in my opinion, and I wanted to share it here.
Both of these cameras use an electro-mechanical sprocket counting mechanism to govern the film advance. The sprocket in the film chamber is free spinning, as opposed to geared like older cameras. As the film passes over the sprocket, a rotary contact spins, intermittently opening and closing an electrical connection. The microcontroller in the camera counts the pulses and stops the film advance once the appropriate number has been reached. The mod involves making a new PCB with different spacing for the rotary contact. The PZ-1p, for example, has a PCB with 8 contact switches per revolution and is geared so that 8 pulses equals an 8 sprocket advance, or 38 mm. Changing the contact PCB to have 12 contacts instead of 8 will shorten the film advance to 25.3 mm, which gives enough room for a 24 mm wide frame with 1.3 mm spacing.
Custom PCBs are quite easy and cheap to get made. The layout can be done in free software such as KiCad, although I recommend drawing the contact geometry in proper CAD software and transferring it over. That will give you much more control over the precise dimensions of the pads. I've started a github repo where the PCB design files are stored as well as other miscellaneous info related to modding cameras.
https://github.com/vandergus/sprocket-mods/wiki
Replacing the PCB in the PZ-1p is very simple as it's accessible directly under the bottom cover. All the same, I put a step-by-step guide up on iFixit to make things crystal clear. For masking the frame opening, I like to use 7 mil (0.18 mm) black mylar sheets. You have to be precise with your cuts and it may take a few tries but it's quite easy to work with. The viewfinder also needs to be changed to represent the smaller frame size. You can either scribe lines onto the focusing screen or make another mask out of the mylar and install it under the focusing screen. Just make sure to do it in a way that doesn't affect the accuracy of the focusing in the viewfinder.
The most fun thing about modding these cameras is taking advantage of the ridiculous compatibility of the Pentax K-mount. Not only can you mount older manual focus lenses, but you can also use more modern digital era lenses. Lenses designed for cropped digital sensors don't usually have a home on film cameras, but when you crop the film, they work with no problem. One of my favorite lenses is the DA 21mm f3.2 Limited. It's tiny, it's wide, it's sharp, and it's so much fun to use on a run-and-gun camera that has 72 frames to play with.
So far I've only modded a couple Pentax cameras but I'm confident there are a lot more where the same idea could be applied. There's a list of potentially compatible camera models on the github page. Take a look to see if there's anything interesting, and if you have personal experience with a camera that meets the criteria, please let me know and I'll add it to the list.
Both of these cameras use an electro-mechanical sprocket counting mechanism to govern the film advance. The sprocket in the film chamber is free spinning, as opposed to geared like older cameras. As the film passes over the sprocket, a rotary contact spins, intermittently opening and closing an electrical connection. The microcontroller in the camera counts the pulses and stops the film advance once the appropriate number has been reached. The mod involves making a new PCB with different spacing for the rotary contact. The PZ-1p, for example, has a PCB with 8 contact switches per revolution and is geared so that 8 pulses equals an 8 sprocket advance, or 38 mm. Changing the contact PCB to have 12 contacts instead of 8 will shorten the film advance to 25.3 mm, which gives enough room for a 24 mm wide frame with 1.3 mm spacing.
Custom PCBs are quite easy and cheap to get made. The layout can be done in free software such as KiCad, although I recommend drawing the contact geometry in proper CAD software and transferring it over. That will give you much more control over the precise dimensions of the pads. I've started a github repo where the PCB design files are stored as well as other miscellaneous info related to modding cameras.
https://github.com/vandergus/sprocket-mods/wiki
Replacing the PCB in the PZ-1p is very simple as it's accessible directly under the bottom cover. All the same, I put a step-by-step guide up on iFixit to make things crystal clear. For masking the frame opening, I like to use 7 mil (0.18 mm) black mylar sheets. You have to be precise with your cuts and it may take a few tries but it's quite easy to work with. The viewfinder also needs to be changed to represent the smaller frame size. You can either scribe lines onto the focusing screen or make another mask out of the mylar and install it under the focusing screen. Just make sure to do it in a way that doesn't affect the accuracy of the focusing in the viewfinder.
The most fun thing about modding these cameras is taking advantage of the ridiculous compatibility of the Pentax K-mount. Not only can you mount older manual focus lenses, but you can also use more modern digital era lenses. Lenses designed for cropped digital sensors don't usually have a home on film cameras, but when you crop the film, they work with no problem. One of my favorite lenses is the DA 21mm f3.2 Limited. It's tiny, it's wide, it's sharp, and it's so much fun to use on a run-and-gun camera that has 72 frames to play with.
So far I've only modded a couple Pentax cameras but I'm confident there are a lot more where the same idea could be applied. There's a list of potentially compatible camera models on the github page. Take a look to see if there's anything interesting, and if you have personal experience with a camera that meets the criteria, please let me know and I'll add it to the list.