The adjective “analogous” is from the Greek word analogos, meaning “comparable in certain respects”. From this comes the noun “analogue”, which is used to name a thing that is similar to another thing (e.g. The ethos of “return love for hatred” is a Taoist analogue to Christianity’s “love thy enemy“).
This name applied to film photography therefore seems paradoxical, since it serves to highlight the differences between film and digital photography via use of a term that is more correctly used to recognise similarities.
Analogue has a further specialised meaning. It refers to a signal where the output is proportional to the input, normally in relation to the combination of a device and a media that can together measure, record, or reproduce continuous information.
For example, older telephones converted the vibration of sounds to electric current, which travelled a wire, and upon reaching its destination was converted back into amplified vibrations. A tape recorder converted sound information to magnetism on the surface of the tape, and these fields were later converted into electrical current by the reading head, which was in turn amplified and transformed into vibration of a speaker.
On this basis, the sensor in a digital camera is also an analogue system. Each of the many millions of pixels in the sensor is a light-sensitive photocell, which generates a tiny electrical current in response to light: the brighter the light, the stronger the current. It only becomes a digital system when the brightness levels are coded into the binary (digital) record of that image.
The word “digital” comes from digit, as in fingers and toes. We count on our fingers (sometimes our toes), and so digit has also come to mean numbers. Digital systems use numbers to store and manipulate information. But I digress…
Film photography is not a true analogue process: it’s a chemical process whereby exposing light sensitive photographic film requires chemical solutions to develop and stabilize the image.
So, there’s another irony to our new terminology. Digital photography is underpinned by an analogue system, and film photography is not a true analogue process. Only the first non-film cameras were wholly analogue systems: they recorded pixel signals continuously, as videotape machines did.
To add further confusing, there are two different spellings of the word. “Analogue” is the traditional English spelling, while the phonetically simplified “analog” is American. However, in the USA both words are used. Analog generally refers to electronics devices, while analogue is often reserved for use in the sense something that bears a resemblance to something else (or so I understand).