How-to: Convert an automatic Polaroid pack film camera to use manual shutter speeds

Back in 1960s, automatic exposure was an amazing advance in photography. Polaroid, in its quest to make a really easy-to-use camera, made most of its cameras with only automatic exposure. I mean, who needed anything else? Fast forward to today and it seems automatic exposure has lost its mojo. Complete control over shutter and aperture is the order of the day.

I had in my possession a bunch of automatic cameras, so I got to thinking, “how hard would it be to give these wonderful cameras manual shutter speed capabilities?” I’m not an electronics engineer or anything like that, but I did like to take stuff apart when I was a child….so, I figured that sort of qualified me to dive into this one.

This article covers the process of figuring out how to retrofit manual shutter control on a number of Polaroid Land cameras, as well as the creation of a hybrid manual and auto-exposure system.

Here’s what I cover:

Creating a digital shutter control circuit?

I read about a way to do this with a microcontroller and some software, but the whole process seemed a little daunting to me: putting together a digital timing circuit, programming it, then basically tearing out the analog shutter circuit in the Polaroid camera and replacing it with the new digital one.

I didn’t really like the way the program operated: keeping the shutter solenoid powered up after cocking the shutter until you released it. Besides, would I be betraying the underlying premise of “analog” photography by converting the shutter to digital?

Philosophical musings aside, I thought it might be a LOT easier (and way cheaper) to replace the Polaroid “Electric Eye”, which is basically a variable resistor, with either a potentiometer (another variable resistor) or a resistor array. The camera I was most interested in doing this on was being used to take paper negatives (check out this link for more on that), and it had a piece of black hockey tape over its electric eye, which basically left me with the bulb option as the only shutter speed. The exposure had to be a second or more since it’s hard to try accurately controlling the shutter speed any faster than that with a cable release.

Replacing the Polaroid Electric Eye

It started simply enough: I took apart the lens body, removed the circuit board, de-soldered the Electric Eye, and attached leads to the terminals it was soldered to.

After reassembling the lens body, I connected a potentiometer (POT) to the leads, and sure enough, turning the dial affected the shutter speed! I quickly discovered however, that the POT didn’t give me the shutter speed range nor the accuracy I needed, so I decided that a resistor array and a 12-point dial switch would work best.

12-point mechanical switches are readily available at the local electronics store, so I got a couple of switches and a package of resistors of varying values and went to work.

Making a manual shutter speed selector

I started by trying to get the shutter speed down to 1 second (my baseline). This ended up needing a resistor with a value of 190 kilohm. Excellent. Next, since 1/2 second is 1/2 of 1, I thought the resistor for that speed would be 1/2 of 190, or 95 kilohms…but it turned out to be 140 kilohms.

This told me there wasn’t a linear relationship between shutter speed and resistance, at least at low shutter speeds, so I made a chart with shutter speeds and resistance values and found a linear relationship (between shutter speed and resistance) started around 1/8 second at 60 kilohms.

Since I only needed shutter speeds up to 1/30 (as this was for paper negatives shot at ISO 3), I decided to fill in the values between shutter speeds since I had 12 points on the switch to play with.

I was doing the shutter tests using the open aperture setting on a Polaroid Land Model 450 camera. The camera has two aperture settings and thought I had the cat in the bag until I tested a resistor using the closed aperture setting — the shutter speed was slower.

It made sense. The closed aperture setting is 2 stops smaller than the open aperture setting, so the shutter speed should be 2 stops slower — this was sort of the case. But as a result, my project was no longer a simple, fool-proof way of controlling the shutter.

The aperture setting would need to be taken into account.

Rather than getting discouraged about this wrinkle, I forged ahead and came up with the following chart showing resistor values plus the respective shutter speeds they translated to for each of the two aperture settings:

kilohm	194	165	140	120	100	80	60	45	30	22.5	15
Open Aperture (speed/sec)	1	3/4	1/2	3/8	1/4	3/15	1/8	3/30	1/15	3/60	1/30
Closed Aperture (speed/sec)	2	1.?	1.5	1.25	1	3/4	1/2	3/8	1/4	3/15	1/8

I concluded from this chart that I could get fairly accurate shutter speeds as slow as 1 second. This didn’t bother me because I would use the bulb setting to make any exposures longer than a second. I would have to remember to add 2 stops to the shutter speed when using the closed setting, but having gone this far, I decided this was workable for me!

Building the resistor array

My first attempt at building an array was a little clumsy. I simply soldered together resistors adding up to the right value to each switch terminal, and stretched them out to one side of the switch.

Getting the right value isn’t straightforward since they don’t make resistors with values like 165K, so I had to get out a resistor calculator and combine resistors either in series or parallel (or both) to get the right value. For instance, two 330K resistors in parallel give a value of 165K. Then I slipped heat-shrinkable tubing over each resistor combination and soldered all the ends together. The two leads from the shutter led back to the battery compartment, where they were soldered to the common terminal on the switch and the ends of the resistors. One switch terminal was left empty for “bulb.”

I had to gut the battery compartment to make the switch fit, then drilled a hole into the side of the camera and installed the switch. I also added a switch template with the shutter speeds on it to match the switch terminals. After testing (and retesting), I had confidence that it was going to work.

Using this resistor array for paper negatives was so freeing! Now I could use larger apertures with shutter speeds of under a second and control the depth of field instead of being limited to smaller apertures (and exposures over a second) during the day. I also had the ability to choose shutter speeds in between the standard ones, which was a bonus since the Polaroid doesn’t have the ability to set the aperture 1/2 way between stops.

Adding faster, faster, faster shutter speeds!

Of course, I couldn’t stop there. I wanted manual shutter control for the other cameras I use with high-speed film. The question was whether the resistance values and shutter speed kept their linear relationship faster than 1/30 second. Since I don’t have the ability to measure shutter speeds above that, I would have to do this with film.

To do this, I simply clipped a piece of 35mm film and taped it (in the dark) to a film cartridge, loaded it into the camera, and metered the exposure for 1/125 second, using a resistor value of 3.75K (4x less than 15K or 1/30 sec). Once exposed, I developed the film, and the exposure looked good. I did the same with 930 ohms or 1/500 sec (4x less than 3.75K or 1/125 sec) and again, the exposure on the negative came out fine.

I could now make a chart with a full range of shutter speeds from 1 sec to 1/1000 sec to use with high-speed film. But I was not satisfied with how the previous resistor array worked out. It was messy and required a lot of space. After researching it a bit, I found a much more compact method of building the array: with accumulated values.

Starting with the lowest value, I could simply build the array using resistors in series, each adding to the value of the previous to give me the value needed for the particular shutter speed. Then I would connect the leads from the electric eye to the common terminal and the resistor coming off the 1/1000 sec terminal. Here’s the chart I came up with:

Shutter Speed	1/1000	1/500	1/250	1/125	1/60	1/30	1/15	1/8	1/4	1/2	1
Resistor value	468	930	1875	3.75K	7.5K	15K	30K	60K	100K	140K	190K
Accumulated	470	470	1K	1.8K	3.9K	6.8K	15K	33K	39K	39K	47K
Actual value	470K	926K	1.9K	3.7K	7.6K	14.4K	29.4K	62K	101K	140K	187K

This chart may look confusing, but I think it’s super cool. Resistors are soldered from each switch terminal to the next, making it much more compact. The first resistor (470 ohms) is soldered to the first switch terminal and connects to one of the leads. The next resistor (470 ohms) is soldered between terminal 1 and two, and so on.

Using BOTH auto and manual exposure modes

For the next camera I did, I was wondering whether it would be possible to keep the electric eye, retaining the automatic exposure option AND my new manual exposure settings.

Doing this would require a third wire from the shutter body and messing with the electric eye itself. Instead of removing it totally, I de-soldered it, bent one of the terminals sideways, and soldered a lead to the bent terminal.

Then I reinstalled the electric eye and soldered the unbent pin to the circuit board, along with a lead, and soldered another lead to the other terminal. Then I installed a switch in the battery compartment which switches between using the resistor array and the electric eye. Here’s the wiring diagram and some work-in-progress images:

I loved the way this was working out! But I had 2 cameras that I had modified for instant film, which didn’t have room anywhere for a resistor array. It took me a while looking at these cameras trying to figure out where to put it, when I remembered a quote out of the opensx70 project blog in which he said, “…then the dongle changed everything.”

Of course! I could make a dongle and plug it into the camera using a jack that automatically switched it from auto exposure to manual when the jack was plugged in!

This Dongle Changed Everything…

Starting at the end: ultimately, this is the manual shutter solution I like best because it retains the option to use the electric eye, provides automatic switching between the two, doesn’t need any space inside the battery compartment (or holes drilled), and only requires one resistor array to control all my cameras, though I did make another array to mount on 100-300 series cameras easier.

To create it, I soldered the three leads coming from the electric eye and its terminals to a 2.5mm jack I installed on the camera body. The 2 leads coming from the electric eye terminals were soldered to the two leads on the jack, and the third lead coming from the bent electric eye terminal was soldered to the switch terminal on the jack, which is normally closed.

Here’s how it looks:

How does it work?

• When there is no plug in the jack, the electric eye is connected to the shutter circuit as normal and provides auto-exposure.
• When a jack is plugged in, the electric eye is disconnected and the resistor array (my manual exposure selector) is used instead.

Next, I 3D printed a box and an interface that fits onto the flash mount on the Polaroid to house the manual shutter speed selector/resistor array I created. Here’s how it looks all hooked up:

Switching between apertures is done by changing the ASA speed setting on the dial, and switching the scene selection switch. This is explained in more detail in this guide I wrote on shooting paper negatives on Polaroid pack film cameras.

The manual shutter speed is affected a full 2-stops by the scene selection switch when set to the “bright sun only” setting. As a reminder of what aperture I’m using, I designed, printed, and laminated labels that sort of look like the original scene selection label. You can find complete instructions and files to do this on my website.

The cost

The parts are cheap — around $10 for the 12-point switch, 11 resistors, a 2.5mm jack and a 2.5mm plug. Of course, you will need a bit of wire and some solder, along with a soldering iron. You could probably make a dongle out of book board if you don’t have a 3D printer, and you may age a bit under all the stress of modifying your camera, but it’s probably worth it!

The benefits

Simple-ish: A camera that has manual shutter capabilities sort of like the sought-after Polaroids 180 and 195! No longer do I have to trust what the Electric Eye tells the camera. Any errors in exposure are my fault and mine alone!

As you may have guessed from my various articles and guides here on EMULSIVE, I love these cameras and really love this new capability.

I hope that this might inspire others to see the potential in that old Polaroid discovered in Grandpa’s attic. Rather than giving it the toss, give it a chance with alternate film and manual shutter control!

Thanks for reading,

~ Jim