A classic example being Star Wars, but I am aware that it was used way before that, at the turn of the century. I get that today it can be done relatively "easily" with the aid of a computer, but back in the analog days, how was it accomplished?
The same way Méliès did his transformations or equal exposure on different planes. By partially blocking camera lens and then rerecording the picture. For wipes there were two easiest methods:
- You've put a screen that was locked into camera mechanism so when the operator turned crank the screen travelled some space before the lens so the film was not fully exposure. Then, movie reel was backed, blocking screen was turned into reverse and turning the crank exposed the previously not exposed film while blocking exposed one from double exposure. This method is usually recognized by the blurred line of the wipe
- Second one was done manually on the assembly line. It was regarded as more labour, time and material consuming as you needed to manually cut each frame by hand and pair it with corresponding one. It was used very rarely and can be recognised by clean wipe line and sometimes "jump" of the wipe while travelling.
A quick search for history of film wipes reveals:
Some extremely effective (and expensive) wipes were used in the otherwise very low-budget Laurel and Hardy short film Thicker than Water. For each of the scene changes in this film, either Laurel or Hardy or both of them would seize a curtain or some other object at the edge of the frame and move it across the screen. The opening frames of the next scene were optically printed onto this object, so that—when the object entirely filled the screen—the movie had "wiped" the last shot of the previous scene and begun the first shot of the next.
The earliest known example of a wipe was George Albert Smith's Mary Jane's Mishap of 1903.