Quantcast

Help a newbie...rainbow effect with a CRT?

Roland @ B4

Active Member
I have set up close to a 1000 CRT's over the years. I set up both projectors that Nigel refers to, the first was a Barco 808 the second a double stacked Barco 1209 and have I never experienced what I could call rainbow.
I would be interested if the same effect can be seen on standard CRT televisions are the refresh rate will be low but the phospors will be pretty much the same.

There are a few people who have glasses that have cromatic problems bending light at differnt angles.
 
R

rob_w

Guest
Hi Roland,

It's not noticable except on thin white lines against black/ dark backgrounds. Try freezing some credits then look straight at the line, then flick your eyes up / down (for horizontal white line/ text), or left/right for vertical lines.

I don't wear glasses for viewing films (yet!). Maybe it's the same as why some people can't see rainbows on DLP machines. I'm pretty sure I saw blue flashes in the moonlight scenes in Pirates of the Carribean at the little odeon Leicester sq, and that uses a 3 chip machine I believe. - I also notice 'judder' on pans at the flicks too..

EDIT - never notice it on my TV though (phillips 32"). That's just got a crap picture:(

Cheers

Rob
 

LV426

Administrator
Staff member
Originally posted by Roland @ B4
I set up both projectors that Nigel refers to....
....and I have absolutely no doubt that they were all giving of their absolute best.

I guess I should say that, at least as far as the Glasgow Event was concerned - I honestly wasn't expecting to see the rainbow effect with CRT technology. When I did see it, it came as a complete surprise. I wasn't looking for it. But there it was. Much less obvious and less nauseating that with 1-chip DLP. But there, nevertheless.

I guess one way to prove this might be to take either still or movie photographs of the screen image, using a shutter speed on the camera much faster than the refresh rate of the device. This would, I guess, reveal any temporal artefacts.
 

Chris Frost

Well-known Member
Originally posted by robwells
...It's not noticable except on thin white lines against black/ dark backgrounds. Try freezing some credits then look straight at the line, then flick your eyes up / down (for horizontal white line/ text), or left/right for vertical lines.
Like Roland, I have set up more CRT projectors than I care to remember, but unlike him I have seen an effect similar to DLP rainbow, but I believe it is more of a 'persistence of vision' thing.

I can get the same effect flicking my eyes across my PC screen as I type this reply. I am also convinced I could replicate the effect with a high contrast image painted onto card so eliminating any question of this effect being caused by CRT or even three chip DLP.

My own thoughts as to the likely trigger for this phenomenon is a combination of image brightness and high contrast.

As for judder in cinema images, I think that is more to do with the frame rate of film (24 f.p.s) producing an animation type effect whenever the camera is panned or there is fast movement across the frame. And yes, it drives me nuts too :)


Regards
 

LV426

Administrator
Staff member
Originally posted by Chris Frost
....but I believe it is more of a 'persistence of vision' thing.

I can get the same effect flicking my eyes across my PC screen as I type this reply. I am also convinced I could replicate the effect with a high contrast image painted onto card so eliminating any question of this effect being caused by CRT or even three chip DLP.

My own thoughts as to the likely trigger for this phenomenon is a combination of image brightness and high contrast.

As for judder in cinema images, I think that is more to do with the frame rate of film (24 f.p.s) producing an animation type effect whenever the camera is panned or there is fast movement across the frame. And yes, it drives me nuts too :)


Regards
Persistence of vision? Plausible, I guess. Is your PC monitor a CRT item? I can't say I've seen anything similar with my LCD monitor - but - as you say, that may be down to lesser contrast.

One of these days, I will get around to photographing some displays and see, for sure, what if any temporal artefacts there are.

As for judder - it is an inevitable by-product of a sequence of still-frames. If the camera shutter speed is too high, especially. A prime (intentional) example is the early fight scene in 'Gladiator'.
 

Roland @ B4

Active Member
Should I confess to using an LCD monitor:blush: But have you ever tried to get a Laptop with a CRT monitor?
 

LV426

Administrator
Staff member
...or, more to the point - have you ever tried CARRYING one?
 

Jeff

Well-known Member
Roland,

I have a nice IBM laptop with built in CRT screen, it even has dual 5 1/4" floppy drives. :)
 

Jeff

Well-known Member


Just for Roland.
 
Top Bottom