Why doesn't a video projector produce screen flicker when recorded??

[yoda313]

I just noticed this phenomenon. Whenever you use a camcorder to record a tube tv you get the annoying screen flicker. I finally noticed that the two demos I did of my video projector were flicker free.

Why is that? What properties do the video projector poses to negate the screen flicker that is recorded off of tube tvs??

[TooLFooL]

progressive scan? quicker refresh rate?

[Noahtuck]

Because you are recording a projection on the wall or screen.
The flicker comes from the picture tube itself when aiming your camcorder directly at the picture tube.
I'm sure someone will come along with a more specific and detailed reason but that's the jist of it.

Also if you look at the end of an infared remote control while perssing a button on it, you don't see anything, the led on the end that transmit's the signal, but if you look at it through a camcorder you can see it light up, i discovered this by accident 10/15+ years ago.
I used to have & use these special little card's that looked like credit cards with a little square of special material on them so you could point a tv/vcr/ect. remote at them and they would lite up so you could check to see if the remote was working.

[edDV]

Identify the projector you are using.

TooLFooL has the basic answer. Interlace scan is difficult to synchronize and near impossible with consumer equipment. Half the lines are scanned at a time for interlace display (odd or even lines). The camcorder is also scanning with interlace scan and almost by definition is out of sync with the display.

Pro camcorders can be sync'd to pro monitors for interlace scan through a process known as gen-lock. It is also possible to electronically sync TV and computer monitors with 24 FPS film (as done in the movies) without the normal heavy flicker.

Simple progressive scan for the display isn't the full solution. The progressive image is painted to the screen and then fades between refresh scans. A camcorder will record this fade as flicker at scan rate. The ways around that is to use longer camcorder exposures but too much of that gets you motion smear.

[Noahtuck]

Well, i've never seen any type of flicker or screen roll through a camcorder off anything except a CRT picture tube which would lead one to believe it's from the picture tube itself, not the picture you are watching.
Where the picture from a projector, regardless of what it is, you are just looking at the picture that is being projected on the wall, not from the projector or CRT tube itself.

[SingSing]

LCD monitor and LCD projector are updated pixel by pixel.

CRT and camcorder CCD are updated line by line. CRT capture often has a horizontal band, where those lines being updated(sweep over). CRT has the same scan rate as your camcorder, but they are not synchronous(exact), so the band appears to walk forward/up or backwar/down on your capture. This is like two cars tarvel about the same speed, you sees the faster car slowly move ahead, even both cars are at 65mph.

[yoda313]

Ok thanks. That makes sense. Its an lcd projector but not progressive by any stretch of the imagination.

[FOO]

The light from a CRT comes from phosphor that is lit by a moving single point electron beam from behind.
The phosphor does stay lit for a short while after the beam is gone but there are times when it is
not lit. So at any given time there are dark areas on the screen.

The LCD has a light that shines through the whole thing continuously, so here are never any
dark areas.