Welcome to ‘Kagoo Explains’ - a series of short articles explaining some of the confusing terminology used to describe technology. This week we’re looking at the magic of instant cameras, and how the chemicals in the film allow you to create a physical photo within seconds!
If you’ve read our run-down of the Best Instant Cameras for 2020, you may have some questions about exactly how this process takes place. Well, the first thing to understand is that while the camera is important, the real magic of instant photography lies hidden in a special type of film.
Instant photography was first invented by Edwin H. Land in 1947, and while the process has changed somewhat, the principles remain the same. When you press the shutter button of an instant camera, it opens the shutter to capture the image of whatever the camera is ‘seeing’, much like the way your eye works. The light from this image enters the lens and is bounced down onto the photosensitive (i.e - it reacts to light) film.
This light then causes a ‘latent image’ to appear on the film - you can see this in the photo to the right. The light particles gathered from the lens react with a chemical compound called ‘silver halide’, causing small clusters of silver atoms to appear on the film, marking it with the image captured by the camera. In black & white film, there is a single layer, while in colour film there are 3 - red, green and blue - and the light only reacts with the layer that matches it’s colour. So red light captured by the camera passes through the green and blue layers, but reacts with the red layer. In this way a full-colour image is built up between all of the layers.
That’s the overly-simple explanation, and if you’re interested in diving deeper, more information can be found in this How Stuff Works article on How Film Works. What’s important is that we now have an image of the scene the camera was pointed at, captured in time. However it’s not ready yet - the film needs to be ‘developed’ to turn it from a ghostly collection of silver particles to a full photo.
Developing film requires yet more special chemicals - called dye developers - that bond with the silver particles in a specific layer, allowing certain colours through but blocking others. With a standard camera this requires manual application of chemicals and some time, but with an instant camera it happens within seconds!
In an unused Polaroid photo, there is a pouch of chemicals squishing around at the bottom of the photo border - if you lightly press a new Polaroid you can feel them there. These chemicals contain everything needed to kick start the chemical reaction and ‘develop’ the photo into a finished print.
How does it work? Well after the latent image has been captured by the camera, the film is pushed through a pair of rollers and out of the camera. The rollers cause the pouch of chemicals to break - they are then smeared evenly over the print like a rolling pin rolling out pizza dough.
The act of smearing the chemicals over the film starts the reaction going - the dye developers work to only let the correct colour dye onto the image from each colour layer, and the final photo is built up by all these different colour layers coming together.
The final piece of the puzzle happens on the surface of the photo. If you’ve ever used an instant camera, you’ll know that the photos start blank, then the photo appears like magic. The reason for this is that the developing process requires time, and until it’s finished the photo has to be protected from any additional light. Since the photosensitive film collects any light shone on it, a group of chemicals called ‘opacifiers’ are mixed in with the dye developers. These cause the top layer of the photo to cloud up, turning it milky white and protecting the film from gathering any additional light until the developing is finished.
Despite what OutKast
may think, you don't actually have to shake Polaroids to speed up the developing. This idea originated with the early generations of instant cameras, where the chemicals came out wet, so needed time (or shaking) to dry. These days? It's not necessary, but damn does it feel satisfying!
These opacifers are timed to break down within seconds, and the clouding starts to clear - leaving you holding your new physical photo! There’s a pretty amazing bit of chemistry happening in that tiny square of white paper, right?