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

vandergus · Nov 25, 2025

There is a small PCB disc attached on top of the sprocket wheel and there are conductive and non-conductive sectors on it:

Yeah, that looks promising!

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?

Unfortunately, some counter PCBs are limited in how they can be modified. The film advance can only be changed in increments, not infinitely adjusted, so you have to get a little lucky. In this case, it sounds like you would have to settle for a pretty wide frame spacing.

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.

I arrived at a very similar criteria after looking at several SLRs. The only additional one being that the sprocket needs to be free spinning. In some early SLRs, the sprocket is still geared directly to the motor, so it's actually pulling the film rather than just spinning as it goes by. Later, the motor advance was geared to the take up spool and the sprocket was just there for counting. I'm not sure how many auto-advancing point-and-shoots would have a geared sprocket.

I hope you keep exploring this idea! Sounds like a great direction to go.

brbo · Nov 26, 2025

As a 135 square format nut (I have Minolta 24 RApid, Altix (non-working), Robot Royal 24 and just barely fighting the urge to get a Tenax) I don't know whether I should hate you @vandergus for only telling us about this now or nominate you for the Nobel prize.

One such mod could've solved all my problems long ago. Or so I tell myself.

Now, lets see how the Nikon F60 mod will go. I don't have one but here seems to be a sea of used ones available for not much money...

Thanks!

flavio81 · Nov 26, 2025

vandergus said:
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.

Brilliant! Such an elegant modification!

I was an electronic hobbist some years ago, so I applaud this initiative.

brbo said:
As a 135 square format nut (I have Minolta 24 RApid, Altix (non-working), Robot Royal 24 and just barely fighting the urge to get a Tenax) I don't know whether I should hate you @vandergus for only telling us about this now or nominate you for the Nobel prize.

Nobel prize!

brbo · Nov 26, 2025

I just remembered that I also got Lomo LC-Wide for the square format. So that's four cameras when I could do it all (and better) with a modified cheap SLR. I mean, that's a nice chunk of money that could be saved if @vandergus would've spilt the beans a bit sooner.

He can count on my vote for Nobel prize only if he comes up with a hack to scan squares on 135 desktop scanners...

blee1996 · Nov 26, 2025

brbo said:
He can count on my vote for Nobel prize only if he comes up with a hack to scan squares on 135 desktop scanners...

I will also nominate him for Nobel Prize if he can figure out better ways to scan square 135 film. I like my Taxona but scanning is a hassle.

baachitraka · Nov 26, 2025

Any chance to get this on Praktica's B series? They are plenty and kind of cheap to find them...

vandergus · Nov 26, 2025

baachitraka said:
Any chance to get this on Praktica's B series? They are plenty and kind of cheap to find them...

Yeah, not really. This method is for a specific set of auto-advancing cameras. Manual advance modifications usually require changing the gearing somewhere in the advance mechanism. It is a bit trickier.

baachitraka · Nov 26, 2025

vandergus said:
Yeah, not really. This method is for a specific set of auto-advancing cameras. Manual advance modifications usually require changing the gearing somewhere in the advance mechanism. It is a bit trickier.

Oh! Thanks.

vusawthis · Nov 26, 2025

I recently got back into film again after two decades break from it. I normally shoot 120 but it's expensive to process and scan (I use a local provider). I don't think I want to develop and scan myself (at least right now). This led me down the path of half frame cameras. I recently acquired a Pen F which I love. And now I want a square 35mm SLR when lead me to this discussion thread. Signed up just now so I can follow.

I'm not technical enough to take on this mod myself - seeding the idea to the OP that he should offer up his services for the conversion. I would happily pay!

Cholentpot · Nov 26, 2025

Camera librarian said:
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.

I have an use the multi tele. It's great but showing it's age, the electronics tend to glitch out if you mess with the settings. Just keep it in full auto everything and its fine.

Jbennett68 · Nov 26, 2025

I wish I could find someone to modify a fully mechanical SLR to 24x65 format. I can’t justify the $$$ for an Xpan.

Cholentpot · Nov 26, 2025

Jbennett68 said:
I wish I could find someone to modify a fully mechanical SLR to 24x65 format. I can’t justify the $$$ for an Xpan.

That's a grail for me. Someone figuring out how to widen the gate of any 35mm camera to get a wider format. Doesn't have to be full Xpan size either. Just go Super 35 size or 52mm which is 1.5 doesn't have to end up the full 62mm

Jbennett68 · Nov 26, 2025

Cholentpot said:
That's a grail for me. Someone figuring out how to widen the gate of any 35mm camera to get a wider format. Doesn't have to be full Xpan size either. Just go Super 35 size or 52mm which is 1.5 doesn't have to end up the full 62mm

I’m seriously considering the ChromaPan 3d printed option. But I’d rather have a modified vintage metal body.

blee1996 · Nov 26, 2025

I think our own @OAPOli has attempted to widen the film gates of several 35mm film cameras. I got one of them parts camera. But in the end I decided to go the Holga 135 Pan route instead, and pretty happy with what I built.

reddesert · Nov 26, 2025

I have widened the film gate of a (older, mechanical) 35mm SLR. It's an unfinished project, although it's more or less at the stage where I could put a lens on and experiment with it, still needs some additional baffle/light seal work. The enlarged film gate SLR conversion is a significant modification, because you have to remove the shutter, mirror box and viewfinder, and mount a lens with shutter in front (or use a lens cap shutter). And then you need to disable the wind/shutter interlock and wind 1.5-2x times per frame.

Keeping on topic for this thread, it would be kind of cool to combine the enlarged film gate with an electronic-film-counter modification so that it correctly measured the film advance. However, one would have to figure out how to gut the shutter area while keeping the electronics related to the sprocket wheel and film counter. Success might be very model-dependent.

Cholentpot · Nov 26, 2025

reddesert said:
I have widened the film gate of a (older, mechanical) 35mm SLR. It's an unfinished project, although it's more or less at the stage where I could put a lens on and experiment with it, still needs some additional baffle/light seal work. The enlarged film gate SLR conversion is a significant modification, because you have to remove the shutter, mirror box and viewfinder, and mount a lens with shutter in front (or use a lens cap shutter). And then you need to disable the wind/shutter interlock and wind 1.5-2x times per frame.

Keeping on topic for this thread, it would be kind of cool to combine the enlarged film gate with an electronic-film-counter modification so that it correctly measured the film advance. However, one would have to figure out how to gut the shutter area while keeping the electronics related to the sprocket wheel and film counter. Success might be very model-dependent.

Don't need it to be an SLR. A rangefinder would work too, even a point and shoot. Only thing that wouldn't excite me is a scale focus camera or fixed. I want some sort of focus confirming camera that does wide shots.

I did it with a cheap 120 TLR. I taped baffled inside the body and got 6x3 images.

reddesert · Nov 26, 2025

Cholentpot said:
Don't need it to be an SLR. A rangefinder would work too, even a point and shoot. Only thing that wouldn't excite me is a scale focus camera or fixed. I want some sort of focus confirming camera that does wide shots.

I did it with a cheap 120 TLR. I taped baffled inside the body and got 6x3 images.

It helps to be realistic about this project, or to look carefully inside some cameras. The reason I did an SLR is that there is enough room next to the film gate to cut something away to enlarge the film area. That room probably exists because that's where the focal plane shutter sat (before I defenestrated it). It would be kind of interesting to try the conversion on a leaf shutter rangefinder (like a Yashica, or Konica auto S2), but those usually have much less room on either side of the film gate. A typical P&S has nearly no room to extend the film gate. If one wants to make heavy modifications to a camera by substantially enlarging the format size, one has to be prepared to accept compromises like scale focus, or spend a lot of time/money on engineering a focusing system.

Cropping a TLR is cool, but it's a bit like the cropped-panoramic format on film P&Ses - it has a higher aspect ratio, but the lens isn't actually a wider angle than the uncropped version.

OAPOli · Nov 27, 2025

I've modded a few cameras to take RF-coupled panoramic photos. But that's off-topic for this thread. You can check my flickr for a tease.

Cholentpot · Nov 27, 2025

reddesert said:
It helps to be realistic about this project, or to look carefully inside some cameras. The reason I did an SLR is that there is enough room next to the film gate to cut something away to enlarge the film area. That room probably exists because that's where the focal plane shutter sat (before I defenestrated it). It would be kind of interesting to try the conversion on a leaf shutter rangefinder (like a Yashica, or Konica auto S2), but those usually have much less room on either side of the film gate. A typical P&S has nearly no room to extend the film gate. If one wants to make heavy modifications to a camera by substantially enlarging the format size, one has to be prepared to accept compromises like scale focus, or spend a lot of time/money on engineering a focusing system.

Cropping a TLR is cool, but it's a bit like the cropped-panoramic format on film P&Ses - it has a higher aspect ratio, but the lens isn't actually a wider angle than the uncropped version.

With the TLR though you're not wasting film. And there's still loads of resolution.

Donald Qualls · Dec 1, 2025

Jbennett68 said:
modify a fully mechanical SLR to 24x65 format.

On the heavy side (WAY on the heavy side!) but an RB67 does a pretty good job putting 24x67(ish) on 35 mm film. With image over the sprockets, if you like that. There are 3D print or commercially made masks for 35 mm film to fit the RB67 backs, too...

Cholentpot · Dec 1, 2025

Scanned a roll that I tried Pano on the half-frame. Didn't work out too well. I'll have to try again. The pano worked but the focus did not.

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

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