>>3649969It's kind of complicated to explain, but easy to show. Here's a clip of what a rangefinder's viewfinder looks like:
https://youtu.be/QAmjugcBkmQBasically, you have a little rectangular bit in the middle (the rangefinder patch) which has a second view overlaid with the normal viewfinder view. When you turn the focus dial on the lens, this view in the rangefinder patch moves. When the two views line up, the bits that are lined up are going to be in focus.
Alternately, a lot of rangefinder shooters zone focus. There are markings on most manual lenses that show where the lens is focused, and lines with aperture numbers on them. So it'll be like
16|....11|....8|...4|...|...|4...|8...|11....|16
The middle line points to the distance that the lens is perfectly focused. The 4 lines will point to where the near and far limits of the depth of field if it's at f/4. The 8 lines will point to the near and far limits for f/8, etc. Get good at estimating your distance to your subject, get good at moving the focus dial by feel (often rangefinder lenses have a little tab on them to make this easier), and you can actually focus this way faster than any autofocus system.
And, of course, a lot of the time,
>>3649974 is correct.