G'day Bill,



05 Dec 96 07:28, Bill Grimsley wrote to Rod Gasson:



 RG>> to IR. However most (if not all) of them have a filter in

 RG>> front of the pickup to block it out.



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



They USED to be easily removable - it was just a matter of setting the

colour balance to Indoor rather than Outdoor and the filter was

physically out of the way - With the newer fully automatic cameras

this is no longer the case though, and the filter is either there or

it isn't (depending on make/model). The electronics compensate for it.



 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.



 BG> That won't do at all, then.  It simply won't be sensitive enough for

 BG> the intended application.



Probably not...   however, I was being a little conservative, and as

Keith (I think it was) reported, his camera detected the IR from his

remote control from about 15ft away.   It still only detects the

source of infrared though, rather than any beams of it, and although

the theory is that you should be able to scatter this light (with

smoke, etc) and see the beam, my experiments at this were fruitless.



 BG>> However, given that almost all video cameras now use an IR beam

 BG>> for their auto-focus detectors,



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

 RG>> camcorders for several years now..



 BG> Really?  I know I don't normally repair them, but all of the (older)

 BG> camcorders I do look at have had IR auto-focus (and that includes

 BG> those cameras with CCD pickups).



The transition was pretty swift and without a lot of advertising

hoo-ha.  From a user P.O.V there wasn't much of a change.



 BG> Sure beats the older ultrasonic

 BG> focussing system too...



And the CCD focusing systems are an equally impressive jump as the

switch from ultrasonic to IR was.



 RG>> They generally use a dedicated CCD pickup these days and monitor

 RG>> & adjust the focus for the best frequency response from it

 RG>> (well, that's the simple description). Such cameras actually

 RG>> focus the _image_, unlike the older IR system which basically

 RG>> measured the distance from the object being filmed and adjusted

 RG>> the lens position according to this distance.



 BG> Does this apply to ALL cameras these days, or are some still being

 BG> made with IR auto-focus?



If not all, it would certainly be the majority of them.



 BG> It's just that to date, I've never seen the

 BG> system you describe (or maybe I have, and simply didn't notice it for

 BG> what it was).



Probably the latter.   Such cameras are easy to identify because the

autofocus will work from infinity all the way down to macro. They are

actually good enough to focus on the inside of the lens cap itself.

('Course, with a black lens cap you'll not see this, but many camera's

use a translucent white cap, which makes it easy to see).



Cheers,

Rod



--- FMail 0.94