According Wikipedia plane spotting is a hobby of tracking the movement of aircraft, which is often accomplished by photography. Besides monitoring aircraft, aircraft spotting enthusiasts (who are usually called plane spotters) often also record information regarding airports, air traffic control communications and airline routes.
Over time the hobby has evolved, if only due to the availability of improved technical equipment. In the beginning a plane spotter would have binoculars and a notebook, then photocamera’s became available, radios air band options and scanners. Now there is the internet with the possibility to real time follow aircraft movement of ADS-B transmitting aircraft. In 1999 a definition of plane spotters / aviation photographer was established based on a purely hypothetical question:
Picture yourself out near an airbase all by yourself, and you see a very special aircraft coming in for landing. You have just one chance during landing on which you can either read the serialnumber of with your binoculars or shoot a picture of the aircraft without a readable serial on it. You know you definately won’t get a second chance !
Read it of, I never take my camera to airbases anyway
Read it of, the camera is only for an occasional shot
Read it of, although you had a little doubt what to choose(
Read it of, but with pain in your hart about missing the photo
Read it of, but only after you have made a very tough decision
Miss it because you can’t decide weather to read or shoot
Photograph it, cursing that you have missed the serialnumber
Photograph it, but feeling uncomfortable about missing the serial
Photograph it, the serialnumber is of minor importance anyway
Photograph it, serials are only of use if they can be read on photo
Photograph it, a serial is just paint to brighten up an aircraft
If you choose the first answer, you are an S5, if you choose the second answer, you are an S4, etc. The middle answer is SF (SF = Sience Fiction, such people do not exist), and then the scale increases F1 to F5. The scale does not indicate how fanatic you are in your hobbies, only which of the two hobbies is more important to you.