Before electronic flash became the norm, we used flash bulbs. These were a one-time use bottle of sunlight. Typically they consisted of a glass envelope filled with oxygen. The bulb contained a filament similar to an ordinary tungsten lightbulb. The tips of the support wires upon which the filament was mounted, were tipped with phosphorous. The glass bulb was stuffed with aluminum wool.

Camera shutters are subsets of pocket watches. They contain springs and gears and a switch. Most early cameras were fitted with a shutter mounted just behind the front lens group. This was known as a between-the-lens shutter. Pressing the go button caused the spring loaded leaves of the shutter to open quickly, remain open for a timed interval, and then quickly close. This scheme is not too efficient. When the shutter opens and closes, the blades of the shutter act like a variable aperture. In other words, the shutter runs up and down the f-numbers as it opens and closes. Only at full open was the f-number equal to the pre-set aperture. Typically they operated at about 60% efficiency.

Between-the-lens shutters were popular because the clock-work mechanism allowed nearly perfect flash synchronization. These flash bulbs needed a warm-up time. The shutter switch was closed 20 milliseconds before the shutter reached full open. This was called “M” (for medium) synchronization. The electricity heated the filament. This ignited the phosphorous. The burning phosphorous ignited the aluminum wool. All this took 20 milliseconds (1/50 of a second). Another flashbulb design skipped the aluminum wool, instead using a heavy dose of phosphorous. This bub needs only 5 milliseconds (1/200 of a second) to reach peak brilliance. This was called “F” (fast) synchronization.

The between-the-lens shutter is limited to a top speed of about 1/800 of a second. Plus, every lens needed one. Thus it is impractical for cameras that feature interchangeable lenses. Focal plane shutter solves two issues. 1. It is at the rear of the camera so lenses can be used without built-in shutters. 2. The focal plane shutter can obtain shutter speeds in the 1/1000 + second range. Its disadvantages: 1. To synchronize it with a flash is challenging. Special flash bulbs are needed. This is because the focal plane shutter works by uncovering a slit in a curtain. The go button is pushed, a spring loaded curtain travels the span of layout of the rectangle (film or digital sensor) format size. The curtain travel time is sluggish. The curtain features a narrow slit. As the curtain travels, the slit covers and then uncovers only a portion of the format opening. In other words, the shutter speed is the time of travel of just the slit width. This time is just a fraction of travel time. Because the curtain travel time is long, special flashbulbs were needed. These were called “FP”. They worked by lengthening out the time the aluminum wool used to fully burn. In other words the blitz length was increased to accommodate the sluggish curtain movement time.

The advent of the electronic flash changes the mechanism of synchronization. The electronic flash needs no warm-up time. The duration of the electronic flash is a blitz about 1/800 or even 1/2000 of a second.

The between-the-lens shutter adapts; the switch is closed when the shutter reaches maximum opening (no warm-up time zero delay). This is called “X” synchronization.
The focal plane shutter of the modern SLR and has a big synchronization problem. The electric flash blitz must happen when the shutter is fully open. This means the slit width must be the same size as the format rectangle. Only a slow shutter speed will work. At slow shutters the slit width is super wide. For your camera this is 1/30 of a second. A more modern focal plane shutter with more powerful springs and lighter curtain can synchronize at far faster shutter speeds. Typically this will be about 1/125 of a second, some faster some slower.