Photographing with flash

You have to switch the flash sync contact depending on either flash bulb or speedlight.
When using flash bulb, set the white picture in the window by raising the milled shutter ring and turning it. And when using speedlight, set the red zig zag in the window.

Both circuits of synchro socket and flash sync contact are switched at the same time by doing above.
You can't use apeture-priority system when using flash.
With speedlight, flash synchronization is from slower speed up to 1/125sec.