2016 hit me hard. 100-Series pack film for Polaroid cameras would no longer be produced and it was only a matter of time before all of my packfilm cameras would become orphans. By 2019, my film stash was running low and I was toying with the idea of making these cameras work with other film types. But it wasn’t until 2021 that I was willing to admit pack film would not be coming back, and that the best future for these cameras is to give them the ability to use different film formats. In the back of my mind was my non-working SX-70 Sonar…
The question: should I or shouldn’t I?
I was hoping that I’d somehow figure out how to fix the SX-70 Sonar, but taking off the cover and staring at it for a while convinced me it was beyond my capabilities. Combine that with the fact I already had 3 other SX-70s, and the decision became easier: cannibalize the SX-70 film transport mechanism and make it into a film back that could be mated to a Polaroid pack camera.
That Polaroid camera happened to be a model 450. I’d call it the SX-450.
Even after the decision was made it took me a while to get up the nerve to tear apart an SX-70 Sonar. These cameras are becoming popular and they are an elegantly designed miracle. It seemed such a shame to purposely wreck one permanently.
As a last-ditch attempt to find an alternative, I got a Polaroid box camera (Sun 600) and tore it apart, but found the motor and gear train were too high to fit into a pack camera. So, after watching a few SX-70 disassembly videos, I filed a screwdriver head down to a 1mm square and jumped in with both feet.
SX-70’s are not unlike a puzzle. There were times I wasn’t sure I was going to be able to disassemble it down to the film pack and keep the drive train intact. And even then, I wasn’t sure what I’d be working with once I got there.
Diving deep into the Polaroid SX-70
A few blind clips later, and pressure on the correct points and I had the film mechanism in my hand. Two microswitches on the drive train showed promise for isolating control over film ejection to a simple mechanical means, but to my dismay, both were oriented in the wrong direction.
I needed at least one switch to open at the end of the ejection cycle to stop the motor so it wouldn’t eject all the pictures once it started. After staring at switches and running the ejection motor countless times, I came to the conclusion that the best solution was to turn one of the switches around to work in reverse: once the motor started its ejection sequence (by an ejection switch), this switch would drop off the timing cam and close, giving power to the motor until the timing cam came around again to open it at the end of the cycle and stop the motor. This was way easier said than done.
The switch is small, and has all the correct mounting pins and orientation to work in the direction it was designed for. And, the clearances are very tight inside the gear train where the switch is located. I had to file down the switch housing as well as the switch contacts so they wouldn’t short against the frame. I mounted and tested the ejection sequence and couldn’t believe it when it worked! The wiring was simple: Connect the battery to the switch, then to the motor and back to the battery. Then, connect another push button switch in parallel to the timing micro switch to kick start the motor. Once the motor started, the microswitch would keep it running until the film was ejected, then would turn off…
…or would it? Motors run on a fraction of a second after power is removed, so I had to angle the switch to turn off just before the end of the cycle, or it would run on and catch the next ejection cycle. After calibrating it to work, I realized I was using an old battery. A solid 6 volts made the motor run faster and run on longer, so more adjustments and it seemed to be working reliably. Some epoxy glue hopefully keeps the switch from moving. This was the hardest part of this project.
As for wiring, I ran 4 wires to the camera to make this work: 2 wires from the battery terminals to power it up when using i-type film (which doesn’t have a built-in battery) and to act as a kill switch (if something malfunctions), and 2 wires for the ejection switch. I found out later that the kill switch is essential to keeping the batteries fresh. For some reason, the IC chip controlling the motor draws a bit of power so the kill switch is necessary to keep the batteries from draining when not using it.
Then, as I was putting it back together, I had some difficulty finding wires that were thin enough to fit in the case as I slid it on. The camera uses ribbon cables and even a thin wire has difficulty fitting between the existing ribbon cable and the case. But after finding the right wire, the SX-70 back was ready for deployment onto a pack camera.
The other half of the camera: a Polaroid Model 450
The first step was to remove the entire back door assembly from the Model 450. This meant drilling out 4 rivets holding the hinge assembly on. Once the back was off, I was pleased to see how well the SX-70 back fit onto the pack camera. It was meant to be!
The next step was to compensate for the SX-70 film plane, which I measured was around 18mm farther back from the original. There are two ways to do this:
- Prevent the focusing scissors from opening all the way and,
- Moving the lens/shutter body back by the same amount.
In early tests with method 1, I found that the rangefinder could be calibrated to focus at infinity, but would not be accurate elsewhere. This is because when the focusing scissors are not fully deployed, the focus action does not move the lens body the same amount as when it is deployed completely. This would require a modification to the rangefinder cam, which is a difficult trial and error process.
So, I went with method 2. I made 3 spacers out of sheet metal from the Polaroid back. Two of them were narrow pieces with 3/16” holes drilled 18mm apart center to center, and the third was a wider piece with 2 1/16” pilot holes drilled 18mm apart.
Then, I removed the lens/shutter body from the focusing scissors. I unscrewed the top black cap on the vertical strut holding the lens/shutter body and removed the spacer. If it spins, it can be pulled off revealing a nut underneath which can be removed.
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Then, I removed the nut at the bottom of the vertical strut and removed the strut from the lens/shutter body. If you do this a spring will come out, which can be put aside, along with a wave washer which is saved for reassembly. Then I unscrewed the bottom horizontal strut from the lens/shutter housing.
Then, I cut a piece of 3/16” steel rod to around 88mm, inserted it into the lens/shutter body, and placed the spacers facing forward on the top and bottom of the rod. I fed the vertical strut through the other holes on the spacer and placed the rod spacer on top of the top spacer and screwed it onto the focusing scissors.
Next, I installed the bottom horizontal strut and put the wave washer between that and the focusing scissors, then installed the nut. I screwed the larger spacer onto the lens body on the bottom right side and found a screw to screw it to the horizontal strut. I later designed some spacers to be 3D printed, which made it look a little nicer.
You’ll notice I didn’t replace the spring, which helps unfold the bellows. This is because the bellows doesn’t lock into the closed position anymore. Without the spring, the bellows stays in place when closed, and will close enough to fit inside the case if you don’t fold down the viewfinder. A little modification to the case made it fit with a raised viewfinder.
Putting it all together
Now to the exciting part. I cut some black 10mm closed cell craft foam and lined the edges of the film plane on the Model 450. Then, I cut some strips of thinner black craft foam and lined the edges of the SX-70 film plane, testing the fit until it took a moderate amount of pressure to bottom out on the camera frame.
My goal was to create a light-tight seal between the SX-70 back and the Model 450 camera. I cut 4 metal strips out of an old SX-70 film cartridge and used them to mount the back to the camera. I found the best way was to pre-drill holes and use small short screws to secure the straps to the camera. While pressing down on the back, I pre-drilled the holes to mount the back and screwed the back on, being sure that the wires were fed out at the top near the shutter.
The moment of truth…
Once the back was on, it was time for a test! I used an SX-70 pack (with a battery), and set the camera speed to 150 ASA. As an even more difficult test, I decided to take a picture using the portrait attachment and the flashcube unit. After taking the picture, I shorted the two wires that kick start the ejection motor, and out came the picture!
This newer Polaroid film doesn’t develop in a minute anymore. However, as the faint image emerged I was amazed that both focus and exposure worked!
Finishing projects always seem to take the longest. I got a very small micro switch for the ejection button and mounted it beside the shutter button with glue. Then, I ran the wires to the battery compartment and wired in a kill switch and another switch to change between SX-70/600 film cartridges and i-type (without a battery).
2x AAA battery holders provide power for both the camera and the back. There isn’t much room inside the battery compartment, so I had to remove the left trim piece and cut out all of the plastic which was used to mount the old battery holder. I mounted the kill switch on the back of a trimmed battery compartment door, and tucked the film-type switch into the battery compartment.
As you can see above, black hockey tape covered over the ugly-looking straps holding it together, as well as the gap across the top with the wires. I had to leave a little slot open to access the film door latch on the SX-70 back. Opening the back requires inserting a thin piece of something into that slot and levering up to press the lever down which opens the film door.
Should I talk about the reversed elephant in the room? Yes, the resulting pictures are horizontally reversed. SX-70 film is exposed from the front, meaning it will show what the lens projects onto it. SX-70 cameras reverse the lens-reversed image again by an angled mirror in its path. The only way to reverse the reversed image is by a mirror. So, in case I need to take a picture of something that has writing on it, I made a lens, electric eye, and viewfinder attachments which all have mirrors at 45 degrees.
I found using the camera sideways is quite difficult, but using it like a TLR camera is more intuitive. Of course, using it like a TLR puts the wider white border on the side of the picture, so I’ll have to learn to use it sideways. The mirror kit? Well, it needs a little tweaking since the framing is off a bit and the flash doesn’t cover the right side of the photo.
This project isn’t for the faint of heart. But the rewards are great. Yes, you can use an SX-70 camera to take pictures with SX-70 film. And you can modify an SX-70 camera to use 600 and i-type film. But extending the bellows, focusing by lining up the images inside the rangefinder and pushing levers back and forth, using high-power flashcubes indoors, and using a smaller aperture (f/25) outdoors are all unique to a pack film camera. And, I can take pictures once again with my Polaroid model 450, which makes me happy!
More sample shots (and ones of the SX-450 itself) follow below!
Thanks for reading. Looking forward to hearing your thoughts below.
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Wow. This is really something. I admire the thinking and ingenuity here. I could never do something like this. Bravo!
This is really fun! Thanks for sharing.