Quote Originally Posted by gnashings
Just one more thing - could someone please explain to me the significance of "Copal Square" shutter design? How is it different from other focal plain shutters? What are the pros and cons? I understand this EF has metal curtains...is that good or bad (or depending on application?) Thanks!
The Copal Square shutter was the first propriety focal plane shutter and was instrumental in popularising the 35mm reflex. Before the Copal Square, the horizontal cloth shutter is structually more entrenched within the construction of the camera and was made by the camera maker as well, but the advent of the Copal Square means that the intricacy of shutter design and construction is taken care of; just bolt the thing in and you're done. Being a metal vertical shutter it also means that it can X-synchronise at at least one stop faster than horizontal shutters, and being a well-built and pretty much self-contained unit, its reliability is very good too.

The Copal Square used in the Canon EF is of a hybrid design: the fast speeds are mechanically timed but the slow speed electronically timed.