What a New Brain Buys You
Four things, only one of which is the film compatibility everybody asks about first.
1. Metering that measures the right thing
This is the part that separates our board from the obvious way to build a replacement, and it is worth understanding before you spend $590.
The original SX-70 does not meter the scene and then calculate a shutter speed. It opens the shutter and watches the light arrive. A photodiode feeds current into a capacitor, charge builds while the exposure is actually happening, and when it crosses a threshold a solenoid slams the blades shut. Ken Shirriff, who has decapped and photographed the original Polaroid chips, puts it plainly: the film's exposure depends on the total amount of light received, which is the same value that the integration calculates.
That distinction is the whole ballgame. The camera is measuring the actual quantity that decides whether your photograph is correctly exposed, instead of predicting it.
The easy way to build a replacement board is to sample the light before the shutter opens, compute a time in software, and count it out on a microcontroller clock. That works, and in flat daylight you would never know the difference. It also throws away everything the integrator was good at. Our V2 keeps the analog cell: a modern photodiode in the 1972 topology. Three things follow from that.
Light that changes during the exposure still counts. SX-70 exposures run long in dim light, sometimes several seconds. A car goes past, someone turns on a lamp, the cloud moves. An integrating circuit closes the shutter when the film has had enough, whenever that is. A pre-computed exposure locked in its answer the instant you pressed the button and has no idea any of that happened.
Flash gets genuinely metered. Flash light arrives during the exposure, and how much of it comes back depends on distance, on reflectance, on what is behind your subject. A cell that is still counting sees the return and terminates on it, which is the same principle as off-the-film flash metering in a good SLR. A board computing in advance can only estimate the flash from the focus distance and hope. That is why flash metering is on the feature list at all.
There are no steps. An analog integrator is continuous. A digital board picks from a list of shutter values. On an f/8 lens shooting instant film this is the smallest of the three, but it is not nothing.
So the upgrade here is not the architecture. Polaroid got that right in 1972. The upgrade is the components. A fifty year old photodiode and a fifty year old capacitor drift, and they drift quietly: not a dramatic failure, just frames that come back a little thin or a little heavy and an owner who assumes that is how the camera looks. New parts in the original circuit means the camera meters the way Land's engineers intended and keeps doing it.
2. Any Polaroid film you can currently buy
SX-70 film is ISO 160. Polaroid 600 and i-Type are ISO 640. Folding cameras could only shoot SX-70, unless they were modified to shoot 600, but then that is permanent.
The other traditional fix is a neutral density filter, a gel over the pack or a filter in front of the electric eye, cutting about two stops so the camera's fixed assumption lands correctly. It works. It also throws away two stops of light on a lens that opens to f/8, in a camera whose shutter tops out around 1/175. On a bright afternoon you will not notice. Indoors, at dusk, in a bar, anywhere you actually want an instant photograph, you have taken a slow camera and made it two stops slower.
A board that knows what is in the camera does not need the filter. Flip the switch, it meters for 640 and exposes for 640, and you keep both stops. No gel, no tools, no disassembly, and you can change your mind between packs.
OpenSX70: What It Is and Why Every SX-70 We Sell Has One
Almost everything on a Polaroid SX-70 can be fixed forever. The gear train cleans up. The mirror re-silvers. The rollers clean, the seals get replaced, the leather comes off and goes back on in whatever color you want. We have been rebuilding the entire SX-70 line for over a decade and the mechanical side holds no mysteries. There is exactly one part that was never fixable, and it is the one that decides whether the camera works at all: the electronic control module Polaroid sealed into the body in 1972. OpenSX70 replaces it. That single swap turns out to fix several unrelated problems at once, which is why every SX-70 that leaves our shop now has one.
The One Part That Was Never Fixable
Edwin Land's SX-70 was the first instant SLR ever built and the engineering is still absurd. A 116mm f/8 four element glass lens. Manual focus from 10.4 inches to infinity, through the taking lens, via a folding mirror path. An aluminum body that goes from flat to shooting in one motion.
Running all of it is the electronic control module, a board designed in the same years and the same idiom as the Apollo guidance hardware. It reads the scene through a photocell, sets the exposure, fires the shutter, drives the motor, flips the mirror, and times the ejection. Nothing on the camera happens without it.
Two things follow from that, and both of them are why SX-70s sit in closets.
The first is that the board assumes ISO 160 film, because in 1972 the only pack that existed was ISO 160. It has no input for anything else. When Polaroid's modern factory settled on 600 speed as the volume product, every surviving SX-70 became a camera aimed at film it could not meter for.
The second is that these boards fail, and nobody makes another one. Fifty year old solder joints crack, capacitors dry out, and the biggest issue is the photocell becomes worn and covered in fungus, the metering barely works- and they can only be cleaned so well. When a board dies, the camera is finished: there is no new-old-stock supply, no service manual that gets you to a component level fix, and no replacement to buy. A perfect body with a dead board was, until recently, a shelf ornament with a very good lens on it.
What OpenSX70 Actually Is
OpenSX70 is an open source project started in early 2017 and run by an engineer named Joaquin, and Zane (and more friends). The idea is simple and slightly heretical: do not repair the 1972 board, replace it with a modern Arduino-based one you can program.
This is a transplant, not a modification. The new board takes over every job the old one had, then adds jobs the old one was never capable of, because a programmable board can be told things a hardwired one cannot. That is the whole conceptual leap. The SX-70's behavior stops being a fact of its manufacture and becomes a matter of firmware.
It was not the first attempt to modernize an SX-70. It is however the only one that uses an analog metering method, the same way the original board uses. A closed modification is only as good as whoever made it and only lasts as long as they stay interested. An open design outlives its author, which for a camera that has already outlived its manufacturer twice is the only sensible way to do it.
The board we install is our own V2, developed on that foundation and calibrated on our bench for each camera it goes into. The project deserves the credit for the idea and the groundwork. What we add is the part a hobbyist board does not come with: consistent metering across bodies, a tested install, and a warranty.
What a New Brain Buys You
Four things, only one of which is the film compatibility everybody asks about first.
1. Metering that measures the right thing
This is the part that separates our board from the obvious way to build a replacement, and it is worth understanding before you spend $590.
The original SX-70 does not meter the scene and then calculate a shutter speed. It opens the shutter and watches the light arrive. A photodiode feeds current into a capacitor, charge builds while the exposure is actually happening, and when it crosses a threshold a solenoid slams the blades shut. Ken Shirriff, who has decapped and photographed the original Polaroid chips, puts it plainly: the film's exposure depends on the total amount of light received, which is the same value that the integration calculates.
That distinction is the whole ballgame. The camera is measuring the actual quantity that decides whether your photograph is correctly exposed, instead of predicting it.
The easy way to build a replacement board is to sample the light before the shutter opens, compute a time in software, and count it out on a microcontroller clock. That works, and in flat daylight you would never know the difference. It also throws away everything the integrator was good at. Our V2 keeps the analog cell: a modern photodiode in the 1972 topology. Three things follow from that.
Light that changes during the exposure still counts. SX-70 exposures run long in dim light, sometimes several seconds. A car goes past, someone turns on a lamp, the cloud moves. An integrating circuit closes the shutter when the film has had enough, whenever that is. A pre-computed exposure locked in its answer the instant you pressed the button and has no idea any of that happened.
Flash gets genuinely metered. Flash light arrives during the exposure, and how much of it comes back depends on distance, on reflectance, on what is behind your subject. A cell that is still counting sees the return and terminates on it, which is the same principle as off-the-film flash metering in a good SLR. A board computing in advance can only estimate the flash from the focus distance and hope. That is why flash metering is on the feature list at all.
There are no steps. An analog integrator is continuous. A digital board picks from a list of shutter values. On an f/8 lens shooting instant film this is the smallest of the three, but it is not nothing.
So the upgrade here is not the architecture. Polaroid got that right in 1972. The upgrade is the components. A fifty year old photodiode and a fifty year old capacitor drift, and they drift quietly: not a dramatic failure, just frames that come back a little thin or a little heavy and an owner who assumes that is how the camera looks. New parts in the original circuit means the camera meters the way Land's engineers intended and keeps doing it.
2. Any Polaroid film you can currently buy
SX-70 film is ISO 160. Polaroid 600 and i-Type are ISO 640. Folding cameras could only shoot SX-70, unless they were modified to shoot 600, but then that is permanent.
The other traditional fix is a neutral density filter, a gel over the pack or a filter in front of the electric eye, cutting about two stops so the camera's fixed assumption lands correctly. It works. It also throws away two stops of light on a lens that opens to f/8, in a camera whose shutter tops out around 1/175. On a bright afternoon you will not notice. Indoors, at dusk, in a bar, anywhere you actually want an instant photograph, you have taken a slow camera and made it two stops slower.
A board that knows what is in the camera does not need the filter. Flip the switch, it meters for 640 and exposes for 640, and you keep both stops. No gel, no tools, no disassembly, and you can change your mind between packs.
3. Behaviors the 1972 board could not have
Some of what a programmable board adds has nothing to do with exposure at all. It is just logic the original could not run.
These are the features nobody asks about and everybody ends up using. At roughly a dollar fifty a frame, knowing a photograph will fail before you take it is worth as much as any exposure improvement, and a print fogged on its way out of the camera is one you paid for and did not get.
4. A 1972 camera that can be updated
Firmware is the quiet consequence of all this. Behavior that used to be fixed in copper is now code, which means a camera you buy today can gain capabilities later without new hardware inside it. That is a genuinely strange sentence to write about a camera designed before the pocket calculator, and it is the reason we went this route rather than doing filter conversions.
The openSX70 platform can, in principle, drive manual shutter speeds, bulb and T modes, double and multiple exposures, a self timer, delayed mirror release to kill vibration, and a PC socket for studio strobes. People are shooting all of that today.
What It Still Cannot Do
Those manual functions are not in the board as we ship it. They need a control dongle, which is in development here and is not finished. It will plug into a camera already carrying our V2 board, so nothing you buy now becomes a dead end, but we are not going to sell you a camera on a feature that is still in development. Treat what is on our shelf as an excellent automatic camera that will shoot any modern Polaroid pack, and treat manual control as something coming later.
Two limits stay put regardless of firmware. The lens is f/8 and the shutter tops out around 1/175. Those are mechanical facts of a folding SLR from 1972, and no board moves them.
Original or Sonar
Both get the same board and the same restoration. The only real difference is how you focus.
The Original at $590 is the purer object and the better camera to learn on. Focusing an SLR by eye at ten inches teaches you more in one pack than an automatic camera will in ten.
The Sonar from $600 bounces an ultrasonic pulse off the subject and racks the lens for you. It is fast and accurate, and sound does not care about glass, so pointed through a window it will focus on the window. That is why the manual override matters. The Sonar is the better party camera and the Original is the better portrait camera. Ten dollars separates them, so buy the focusing method you will actually use.
What the Restoration Involves
The board is the headline and the last step. A new brain in a camera with perished seals and a dry gear train is an expensive way to ruin a pack of film.
Every SX-70 through here gets a full diagnostic of the mechanical and electronic systems, then a complete clean, lubricate and adjust: rollers, gear train, mirror, shutter blades, light seals. The optics come apart and go back together clean. Re-leathering is optional and is where most of the personality comes from. Then the V2 board goes in and gets calibrated against a reference, because a board that meters correctly in one body does not automatically meter correctly in the next.
Everything we sell carries a six month warranty, extendable by another six for $90. If the SX-70 you want to shoot is the one already in your closet, send it instead of buying ours: turnaround is usually eight to twelve days from arrival, and the full scope is on our Polaroid restorations page.
Polaroid SX-70 Original
$590
View ProductFrequently Asked Questions
What is OpenSX70?
An open source project started in 2017 that replaces the Polaroid SX-70's original 1972 electronic control module with a modern Arduino-based board. Because the board is programmable and the design is public, it both revives cameras with dead electronics and adds behavior the original could not perform. The board we install is our own V2, built on that foundation.
Can an SX-70 shoot 600 film?
All of ours can! Not as it left the factory. The original board assumes ISO 160 and 600 film is ISO 640, so a stock SX-70 overexposes it by two stops. The old fix is a two stop neutral density filter. Our board instead switches the camera between ISO 160 and ISO 640 with no filter, so you keep the two stops of light.
Does the board give me manual shutter speeds?
Not yet. Manual speeds, bulb and T, multiple exposure and strobe sync all need a control dongle still in development. It will work with the V2 board already in these cameras, so buying now does not lock you out of it.
Is this better than a filter conversion?
For most people, yes. A filter conversion is cheaper and it works, but it only addresses film speed, and it does so by throwing away two stops on a lens that opens to f/8. The board solves film speed electronically and also replaces the failure-prone module, fixes drifted metering, and adds flash metering, low light warning and hold to eject.
What film should I buy for it?
Either. That is the point. 600 and i-Type are easier to find, come in more special editions and give you more speed. SX-70 film is the original look. Both are on our Polaroid film shelf, and the camera switches between them with a flick.
Where to Start
If you want the best instant photograph a camera can make and you are willing to focus it yourself, buy the SX-70 Original at $590. If you want to hand it to someone at a party and have the picture come out, buy the SX-70 Sonar from $600. Both are rebuilt here, both carry the V2 board, and both come with six months of warranty.
Load either from our Polaroid film shelf, or look through the rest of the Polaroid cameras we have rebuilt. And if yours is in a drawer because it stopped working, that is the exact problem this board was built to solve. Send it to us.
Share Your Shots
Tag your SX-70 prints with #BFCsx70
Griffin Malone
Griffin does construction, project management, some photography, and bartending. When not working you may catch them playing pool, pinball, or biking around Brooklyn.
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