Converting 35mm SLRs to shoot half-frame and square formats

[vandergus]

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.

 

[foc]

Thanks for sharing and showing the square example.

Reminds me of the old Agfa Rapid.

 

[Besk]

That is fantastic. I wish I could do that with a Nikon F2 but am afraid it would be much more involved being a fully mechanical camera.

I have a Minolta 24 Rapid but it is not a SLR with interchangeable lenses.

 

[loccdor]

That's awesome, do you have to do something to get past the 36 exposure limit some of the cameras have, like covering DX codes?

 

[vandergus]

That's awesome, do you have to do something to get past the 36 exposure limit some of the cameras have, like covering DX codes?

So far I haven't had to get tricky with the frame counters. The cameras keep on going past 36 frames. And since they are just displaying a number on a screen rather than incrementing a physical wheel, I even get accurate counts. I usually get ~55 on square and ~75 on half-frame. The rewind isn't triggered until they feel the tension at the end of the roll.

 

[loccdor]

Cool! I think the Canons would limit you if you don't cover the codes. I have a 650 and it doesn't let me go past 36.

 

[vandergus]

Cool! I think the Canons would limit you if you don't cover the codes. I have a 650 and it doesn't let me go past 36.

Thanks, that's good to know. The EOS 650 is on my short list of cameras to experiment with.

 

[blee1996]

Wow very cool project with simple and elegant mod. and thanks for open source on GitHub!

 

[Donald Qualls]

Wow. Now I'm tempted to get a Nikon F60/N60 body to make a half-frame SLR out of it (since that's the only system I have that can take a modern lens and I have a number of manual focus and access to a few auto focus lenses).

 

[vandergus]

Wow. Now I'm tempted to get a late Nikon body to see if I can make a half-frame SLR out of it (since that's the only system I have that can take a modern lens).

The N60/F60 looks really promising. It's the only Nikon body I've cracked open and it has a counter PCB very similar to the Pentax PZ-1p, which was really easy to mod.

I think the N90 is modable and maybe even the F100, which would be...crazy. The N80, N65 and N55, use IR based film advance mechanisms and won't work with this method.

 

[blee1996]

I don't have any of the camera listed on your wiki. But a Nikon N90/F90 or F100 will be indeed crazily good, since I have lots of. Nikon lenses.

 

[Donald Qualls]

The N80, N65 and N55, use IR based film advance mechanisms and won't work with this method.

Roger that -- I'm definitely not competent to disassemble the ROM code, change the advance value (how many places?) and burn a new ROM, never mind replace the physical chip on what's probably a soldered surface mount board. But unsoldering and resoldering two or three or even half a dozen humanly accessible pads on a PCB that does nothing else, I'm pretty confident I can do.

FWIW, the auto focus lenses I have (access to) are from a D70 and D90, both crop sensors, so half frame is a good use for them.

 

[OAPOli]

Really neat project! I wonder if there are compact P&S cameras that could modded the same way?

 

[baachitraka]

wow!!! those square negatives look awesome.

 

[xkaes]

Really neat project! I wonder if there are compact P&S cameras that could modded the same way?

There are already plenty of P&S cameras that are half-frame or square-frame.

 

[Cholentpot]

OP converted one of these machines for me. Excellent work and it's been my go-to all summer. I would love one in square frame too. I have an N60 and a bunch of EOS cameras kicking around. Getting those converted would be amazing.

 

[OAPOli]

There are already plenty of P&S cameras that are half-frame or square-frame.

With AF, AE and motorized advance, taking normal 35mm cartridges? Konica Recorder is the only one I know.

 

[reddesert]

That's really clever. Chapeau.

 

[xkaes]

With AF, AE and motorized advance, taking normal 35mm cartridges? Konica Recorder is the only one I know.

Now you're putting restrictions on what a P&S is. Why not add in a built-in flash to your definition -- as many P&S cameras have? In any case, there are other cameras. The Fuji TW-3 is one half-frame with a 35mm lens and a 105mm lens, AE exposure, motorized 35mm film.

Much depends on what you consider a P&S camera.

 

[Donald Qualls]

Wow, I see N80 bodies for very little money, listed as "tested, working" -- those would require AI lenses or AI converted lenses, correct?

 

[vandergus]

Wow, I see N80 bodies for very little money, listed as "tested, working" -- those would require AI lenses or AI converted lenses, correct?

N80s won't work with this mod, unfortunately. They use IR sensors for controlling film advance rather than rotary contacts.

With what I currently know, I would recommend an N90 if you're looking for something that can use a wide variety of lenses. You can shoot AI lenses in aperture priority and manual mode and modern G lenses in shutter priority and program mode (I think). And it can focus AF-S lenses.

 

[Donald Qualls]

I have a few pre-AI manual lenses, so those would have to be converted -- but I also have (access to) a couple digital-era auto focus zooms.

I meant to type N90; that's what I searched and saw a number of them under $100. I might grab one...

 

[Camera librarian]

Registered to say thanks for this project! I am a big fan of 35mm square format but the cameras using this format are few and far between and unfortunately are also usually quite limited. Having a square-format 35mm SLR was pretty much a dream of mine but to my knowledge, there was only one ever produced, the Mecaflex. And while I would love to have a Mecaflex, I would also like to have both of my kidneys intact So being able to mod some rather advanced SLRs on a budget to shoot native square format is very-very cool!

As for the moddable cameras, the SLRs I currently own all use the IR sensor but I also have a Pentax Zoom 70, the original one. This was reportedly the first-ever compact camera with a built-in (collapsible) zoom lens. Since it was manufactured by Pentax and around the same time as the PZ/MZ series that you found to be moddable, I had a hunch it could be as well. A quick check revealed that indeed it should be. There is a small PCB disc attached on top of the sprocket wheel and there are conductive and non-conductive sectors on it:

The sprocket wheel has 6 teeth and the counter PCB on top has 3 conductive sectors and 3 non-conductive ones in the pattern similar to the radiation danger sign. So I guess it should be possible to turn this camera into half-frame by making the disk with 6 + 6 sectors. But for the square, I am not so sure. Seems like 4+4 sectors will result in too wide spacing and 5+5 sectors will not be enough spacing?

 

[Camera librarian]

With AF, AE and motorized advance, taking normal 35mm cartridges? Konica Recorder is the only one I know.

There are also Yashica Samurai series and rather obscure Canon Sure Shot Multi Tele/Prima Tele/Autoboy Tele 6 that fit your requirements and on top of that also have a zoom lens. Yashica is an SLR and is not extremely compact so might not strictly fit the definition of P&S but Canon is a typical P&S.

As for the P&S that can be modded, there are surely some (also see my post above) but the pool of those is probably not very large. It is actually relatively easy to filter those cameras that can potentially be moddable. They should:
a) Have a sprocket wheel. If there is none, then the camera is using an IR sensor for counting sprocket holes.
b) Display the frame numbers on an LCD screen. If a camera has a small viewing window on top where it displays the frame number, it means there is most probably a mechanical system and not an electronic one.

If both of those requirements are true, there is a high chance the camera might use the sprocket counting system like OP has described and thus could be modded. Most of those cameras will be originating from the beginning-mid 90s so they won't be the most advanced, compact or fast cameras out there but they do exist. Actually, I think the original Olympus mju might be moddable as it fits a) and b) but I don't have one to open up and check. A half-frame Oly mju will be kind of cool, though.

Another issue with modifying P&S is that you would need to also add new frame lines into the viewfinder. It is relatively straightforward in case of SLRs but a less so in case of P&S as their viewfinders are often made into one closed-down plastic-encapsulated assembly that is hard (or sometimes impossible) to open up and tinker with. I guess as the last resort it should be possible to just tape out the sides of the viewfinder to the desired format but that's not a very precise way of doing things.

 

[OAPOli]

@Camera librarian thank you. I'm also interested in the square format in 35mm since it's pretty uncommon. I get that there are many half-frame cameras but square? Not "many"...

I'll be on the look out for a P&S as you described it. I checked the Pentax PC-550 but it has a mechanical counter. But you're right these would be more difficult to modify since they are so compact.