The question Why do the focus points leds in my viewfinder appear shadowed? raises another question for me. How are these indicator lights implemented in typical DSLRs? Are they actually small LEDs etched into the focusing screen, and if so, how do they get their power? Or are they projected/reflected from somewhere?
The new Fujifilm X100 has a "hybrid viewfinder" which can show arbitrary heads-up information, including completely switching to electronic viewfinder mode. Is this a much-further-along extension of the same approach taken in DSLRs, or is it different?
In their review of the Nikon D3S, DPReview says:
The AF points are not etched onto the focusing screen, but are displayed on the LCD layer sandwiched inside it.
Is this correct for this model, and do other models and brands follow the same approach? Are there advantages and disadvantages to different designs?