I'm not asking the question as a beginner (!), but because I am surprised to see mirrorless cameras widely being described as SLRs (where the "R" surely stands for "Reflex"), for example here :
Sony Digital SLR Cameras - Jessops
My understanding is that "Reflex" means "Reflection", ie a mirror is involved. A possible alternative is that it refers to the "reflex" action (as in a knee jerk) of the mirror (again) jumping out of the way when the shutter is pressed as in a traditional SLR; however the latter meaning is belied by the long-established term "Twin Lens Reflex" in which the mirror does not move.
Sony themselves on their website do not describe the A99 II (for example) as a DSLR, but as an "Interchangeable lens mirrorless" (
SLT & DSLR-Like Cameras | Digital SLR-Like Cameras for Professionals | Sony UK). I understand that the mirrorless do in fact contain some sort of translucent mirror, but you can hardly say they have a mirror and call them mirrorless in the same breath (unless you are a salesman of course
).
The Wikipedia entry for "Reflex Camera" (
Reflex camera - Wikipedia) is nonsense IMHO : saying, among other things, "
The twin-lens reflex camera provides both a viewfinder image and the reflected image from the actual camera lens". In fact a TLR does not show the user the view through the "actual camera lens" which will take the picture.
PS : The Sony website is a mess of Javascript and the above link may not work properly, but I've done my best. I notice that the same Javascript automatically put the phase "DSLR-Like" into the link description above, although that term does not appear on that web page anywhere AFAICT.