Normally, after you peel apart the film, you're supposed to throw away the negative, which presents an environmental hazard since it contains caustic chemicals, and admire the print, or try to determine what went wrong using the troubleshooting guide in your Polaroid manual. But I thought it would be interesting to reverse the above procedure to figure out what really happens when you pull those two tabs out. Like, why do you have to pull out two tabs? How does that negative line up with the paper? Where does that complicated negative/positive/chemical combination all fit inside that film pack?
To answer these questions, I tried reconstructing a negative/positive film combination by glue-sticking the print back onto the flimsy tracing type paper that it's originally attached to. I also very carefully dabbed all those caustic chemicals off of the negative and the end where the excess accumulates after passing through the rollers. You may notice two things here. One, is that the negative is totally separate from the positive, and the chemicals are originally in a white pod strategically placed so that the rollers will squish them out between the negative and the print when the big tab is pulled out between the rollers. Ingenious.
Then, I took apart an empty film pack and noticed that there is a divider which the negatives sit behind, away from the positives. A nice curve is built in, so that when the first tab is pulled, the negative will do a 180 degree turn to meet the positive.
The negative lays down facing forward (so that it will get exposed when taking a picture)
Then the divider is layed down on top of it. Of course, this is all assembled in the dark at the factory.
The big tab gets layed down on the other side of the divider, and this is where I remembered that I needed to glue on the first white tab to the back of the big tab. See how the white tab stretches out? This is the part that sticks out of the camera.
Now, the positive, which is attached by that flimsy tracing paper, is pulled over to the right and layed down on top of the white chemical pod, accordian style.
When the first tab is pulled out, it pulls the negative around the corner and pulls the second tab through the rollers. Because the first tab is being pulled out of a different path than the second tab, it rips off. The paper is still not lined up with the negative, but it's getting closer.
When the second tab is pulled, the rollers break open the chemical pod, and the chemicals start squishing out towards the negative. Right when the negative reaches the rollers, the positive lines up with it, since that flimsy tracing paper which is glued to the positive has now taken up the slack, and both negative and positive are pulled through the rollers together. The rollers press the negative and positive together, spreading the chemicals almost perfectly between them.
Schematic
Click here to see a top-view of a film pack in its 3 stages: during exposure, when the first tab is pulled out, and when the big tab is pulled out.
Click here to see a top-view schematic of a roll film camera.
If you'd like to know how the film actually develops, Click here.
