>>2665334The aperture ring is jammed? Is it stuck on A by chance? If so there's a button on the side of the lens that you have to push in and hold while you move the aperture ring from A to f1.4 or 1.8 or whatever.
In response to your flash question, shutter speed doesn't affect the flash output at all. Aperture is what determines how powerful the flash is. Think about it this way:
Flashes fire extremely quick (much faster than 1/1000th of a second). So that means no matter what, your flash will be faster than your shutter. It will have the same power if you shot at 1/1000th of a second vs 1 second. However, if you shoot at f2.8 and then again at f4. The flash power will be half at f4 compared to what it was at f2.8 because the lens opening is letting in half as much light.
The fun thing with flash and shutter speed is you can use the relationship to shoot a long exposure but still freeze action the moment that the flash fires.
On most FD mount Canon cameras I believe the flash sync (which is the fastest shutter speed your camera can shoot when using a flash) is only 1/60th of a second. If you look at your shutter speed dial you'll see a little lightning bolt next to a shutter speed. This is the fastest shutter speed you can use with a flash.
Let me know if you have any other questions!
Here's an example photo where the shutter speed was long and the flash is what froze the action.
