Rod, at 10:49 on Nov 30 1996, you wrote to Bill Grimsley...

DM>> I believe a standard video camera can detect IR, and sees 
DM>> it as a point of light, or whatever.

BG> Rod seems to think so as well, but I'm not convinced

RG> Alas, it is true - The CCD (and tube) cameras are sensitive 
RG> to IR. However most (if not all) of them have a filter in 
RG> front of the pickup to block it out.

A passive glass-type filter presumably, and easily removable?

RG> Even without this filter they are generally not sensitive 
RG> enough to be useful though... they will only just bearly show 
RG> the IR radiation emitted from typical IR remote control when 
RG> pointed directly at the lens from a few inches (sometimes 
RG> feet) away.

That won't do at all, then.  It simply won't be sensitive enough for the
intended application.

BG> However, given that almost all video cameras now use an IR beam for their 
BG> auto-focus detectors,

RG> Not so....  IR beams for AF haven't been used in most 
RG> camcorders for several years now.. 

Really?  I know I don't normally repair them, but all of the (older)
camcorders I do look at have had IR auto-focus (and that includes those
cameras with CCD pickups).  Sure beats the older ultrasonic focussing
system too...

RG> They generally use a dedicated CCD pickup these days and monitor & adjust 
RG> the focus for the best frequency response from it  (well, that's the simple 
RG> description). Such cameras actually focus the _image_, unlike the older IR 
RG> system which basically measured the distance from the object being filmed 
RG> and adjusted the lens position according to this distance.

Does this apply to ALL cameras these days, or are some still being made
with IR auto-focus?  It's just that to date, I've never seen the system you
describe (or maybe I have, and simply didn't notice it for what it was).

Regards, Bill

--- MsgedSQ/2 3.50