there are four controls on this camera that need to be managed to operate the focal-plane shutter. most cameras have two or three shutter controls - a speed selector, a shutter release, and maybe a lever to cock the shutter - so what the hell is going on here
the shutter release is at least sort of normal. it's that 7-shaped lever in the middle, and to trip the shutter you pull the tab on the bottom of it towards the back of the camera. sounds simple enough, but if you cock the shutter (we'll get to how) and hit the release, you won't get a picture.
that's because - as this is really more of a large format camera despite having a 120 back - you need to pull the darkslide. why is there a darkslide on the 120 back? well one reason is so that you can swap backs without exposing any film in them (although you can't do that on this particular model for reasons that mostly aren't important), but the other reason is that if you cock the shutter with the darkslide open it'll expose the film. what?
let's back up a second and talk about how focal plane shutters work on literally every other camera in existence. there are two curtains that can cover the film gate, and when the shutter is cocked the first curtain is closed and the second curtain is open. to fire the shutter at a given speed, the camera releases the first curtain to start uncovering the film, waits the given exposure time, and releases the second curtain which blocks the light again. this means that a) the shutter speed is determined solely by the time between curtain releases, so you can have a single setting for it, and b) you can keep the shutter completely closed while it's being cocked by having the second curtain latch on to the first curtain and pull it back across the frame.
one nuance of this approach (and focal plane shutters in general) is that it does not require that the entirety of the film is exposed at once. for most of my film cameras, the shutter curtains take about 1/60 of a second to cross the frame, but that's okay because if you want a faster time like 1/1000 you can just release the second curtain after 1/1000 of a second anyways and the two curtains will form a tiny little gap that swipes across the gate and only exposes any individual portion of the film for 1/1000 of a second.
the speed graphic works differently. it has one shutter curtain with several different gaps of various sizes in it, and the overall shutter speed is selected by choosing a gap and then also adjusting the speed at which it crosses the film.
this is why you need the darkslide. since there's only one curtain, it can't overlap with the second curtain while you're cocking the shutter - the gap is going to have to go back over the frame, so you put the darkslide back in.
selecting the gap is done at the same time as cocking the shutter. every time you wind that big knob at the top of the camera, it moves to the next smaller gap, and every time you trip the shutter it moves to the next larger gap. that means that if you wind the shutter to anything but the slowest setting and then fire it, it's actually still cocked, just for a completely different shutter speed.
then since there are only four gap widths available (remember, these gaps are physically cut into the shutter curtain so they can't be adjusted on-the-fly like two-curtain shutters do), there's also a fine-adjustment knob down at the bottom that tweaks how wound-up the shutter spring is. it's operated similarly to selecting a gap, where you turn it twice to move up to the next tension level and then click this extremely loud release lever twice to go back to the previous one. of course, there isn't a simple relationship between gap width, spring tension, and shutter speed so there's an enormous lookup table (there are twenty-four possible combinations) attached to the camera. oh and of course since the shutter doesn't really have "cocked" and "released" states (hitting the shutter release will always do something - even if you trip the shutter on the "A" gap setting you can actually do it two more times before it stops making noise) if you forget to "cock the shutter" it won't not work, it'll ruin your photo. that sucks!
so the whole process of using this thing goes something like this:
- meter the scene
- set required aperture on the lens (opening the lens's own shutter, if it has one)
- look up the required shutter speed on the speed table
- set the shutter gap, if it's not already correct
- set the shutter tension, if it's not already correct
- focus through the rangefinder
- compose through the viewfinder
- pull the darkslide
- trip the shutter
- return the darkslide
- unlock the film advance
- advance the film
screwing up any of those steps will at best give you a poorly exposed image and very well might completely ruin it. it's no point-and-shoot!