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

Nebby

Novice Member
Hi All

I've just begun to dip my toes into the wonderful world of CRT!

I've recently purchased a second hand Seleco 320...

While I have the option of paying for a professional install, I am keen to learn more about this new 'toy', and have had a crack at setting things up myself.

After a few nights spent tweaking under dimmed lights, I'd say I'm within touching distance of a nice picture. However...

The CRT is currently connected to a DVD player (Pioneer DV-353)by SVHS cable (will switch to component video output soon). When watching a movie (I've tested a few), I seem to be experiencing what I can only liken to a 'rainbow effect' if I happen to glance away from the screen. This sometimes occurs if the action involves fast movement.

I've experienced the 'rainbow effect' before when looking at a dlp projector, but was under the impression that I shouldn't experience the condition with a CRT. This leads me to believe that I've gone wrong somewhere during set-up, although I've started from scratch two or three times now, just in case I' missed something along the way.

While I'm happy to pay for the professional install, I can't stand being beaten! Given my lack of CRT experience, if the above suggests a particular problem or setting I need to look at, I'd be most grateful for any help / advice.

Cheers
 
Don't panic, i think you'll find this is normal. I run a Barco 7LT froma Denon 2900 and expereince the same. The PJ was professionally installed. You may find that you are particularly sensitive to the effect. I found that DLP gave me a headache and was very distracting, whereas with CRT it is only on light against black, and in fairness you do have to exagerate your eye movement dramatically to see it. Sit back, relax and enjoy the world's best projectors.... CRT
 

Nebby

Novice Member
Hi mrxfilms

Thanks for the reply and encouragement. I guess I'll keep tweaking...it's all part of the fun, I guess...and experimenting with "Y/C delay", "blue stretch", "peaking", "comb filter" and so on.

Do you think there's some kind of conspiracy going on with av equipment manufacturers? The manual that came with the Seleco is a classic...it shows you how to adjust the settings outlined above, but then fails to explain what effect any adjustment will have on the picture!!!

Do you know of any glossary's that I might find on-line, that explain these dark arts?

Nebby
 

cessquill

Active Member
I've got a fair amount of information with just google searches. My manual is the same. Yes, I'm aware how to turn things up and down - all the settings adjust exactly the same. I want to know what they do.

Some of the Italian-English translation in mine means that when they do try to explain, it just sounds like rubbish.
 
Hello Nebby,
There is a web site called crtprojectors.co.uk who have bags of info on CRT's. They have a slight bias towards Barco but plenty of info on others. When i first decide to go the way of CRT 2 years ago, this site provided a good grounding of info. Print the FAQ section out and you will have plenty of toilet reading.
Regards
Pete B
 

LV426

Administrator
Staff member
Some 'experts' initially deny that CRT rainbows are possible. Indeed, a few years ago at 'The Event' I saw this effect, commented on it, and it was dismissed as imagination by the expert presenter.

Yet there they are. Others have seen them too (although very few people have 'fast' enough vision).

I can only assume that the the coloured tubes are not energised concurrently, but consecutively, and, coupled with the intermittent nature inherent (ie unavoidably flickering) of any CRT presentation, this does indeed produce, effectively, the same thing as 1-chip DLPs do.

To reduce (but never remove) it for a CRT you need to use an external scaler to ramp up the refresh rate as high as the projector will take.
 

Nebby

Novice Member
Hi Pete

Just had a quick look at the site you suggested...looks like I've got plenty of reading material!

Thanks for the help
 

Nebby

Novice Member
And thanks to you too Nigel...although I have to admit, being such a newbie I only understood the last paragraph of your post (I tend to pick up on things that involve spending money!) and, of course, your sign-off reference to one of the greatest movies ever made!
 

Jeff

Well-known Member
Originally posted by nigel

To reduce (but never remove) it for a CRT you need to use an external scaler to ramp up the refresh rate as high as the projector will take.
This has a serious impact on picture quality, if you see rainbows on CRTs and flicker bothers you a lot then I would suggest that CRT isn't a solution for you.

Despite the fact that I see rainbows on even the best single chip DLP projectors and 50Hz bothers me on large(28"+) CRT TV's, I run my CRT projector at 48Hz for NTSC film and 50Hz for PAL and enjoy the experience greatly.

Each to his own as they say.
 

chrisgeary

Member
yes i can detect a slight rainbow effect with my 801s, but i have to rapidly move my eye from left to right to get it (a thoroughly unnatural experience - even after a bottle of wine!) - just moving your eye from the left of the screen to the right isnt enough - so i never notice it! if you haven't seen an LCD or DLP projector, you should.. you only have move a millimeter and the rainbow effect strikes!
 

LV426

Administrator
Staff member
Originally posted by chrisgeary
if you haven't seen an LCD or DLP projector, you should.. you only have move a millimeter and the rainbow effect strikes!
Do you mean that BOTH DLPs AND LCDs have rainbows?

If yes - you are seriously misguided. Although they aren't without their other shortcomings - LCDs do not, and never have, suffered form any rainbow or any other temporal artefact. They all produce a constant, unflickering image (assuming, of course, that they are working correctly).
 

chrisgeary

Member
yeah i have seen LCDs produce the rainbow effect. i have a friend who has a compaq jobby.. its very noticeable. no its not DLP ;o)
 

Jeff

Well-known Member
Nigel, see what you've started. Rainbows on LCOS anyone?
 

LV426

Administrator
Staff member
I started it?

I'm sorry chrisgeary. With some (only some) knowledge about how these things work I seriously doubt that what you saw was anything other than the product of a deranged mind. In any case, if true in the specific case, it's probably unique; certainly very very rare for an LCD to produce any kind of temporal artefact. Really - they just can't.
 

Jeff

Well-known Member
Originally posted by nigel
Really - they just can't.
Isn't this what was said when you claimed to see rainbows with CRTs? :)
 
R

rob_w

Guest
I can catch a rainbow on my barco 800 (720x480x72Hz):(

But only with white on black stuff (credits etc), and only if I move my eyes about.....

My old dlp on the other hand :rotfl:

Never noticed it on lcd though....

Could it be linked to the screen gain? - I use harkness hall perlux140. Meant to be quite a small viewing angle.

Rob
 

chrisgeary

Member
nigel: i really don't appreciate your tone. so far you have stated that i have a deranged and misguided mind without any real reason. i think you could show some respect for the views and opinions of others. why must you resort to patronising personal attacks rather than just debating the issues and opinions presented?
the thread is rainbow effects with CRT. perhaps we are not talking about the same thing so ill be clear about what i mean: i have seen, quite vividly, a streak of multicolour as my eyes move from one part of an LCD projected image to another. i can barely discern it with CRT, as can the thread-starter and as mrxfilms stated, you have to really try to see it. i stated that it is much more noticeable with LCD/DLP forgetting that nebby already knows this! duh, sorry.
you seem quite sure that your view is the only and correct one regarding LCD and rainbows and that my experience is invalid. yet by your own admission in other threads, some people see it, some don't. so can you not accept that i can see it, really quite vividly and am not deranged nor misguided?? perhaps there was some other factor that lead to me seeing it, and it was not the LCD equipment at all.. perhaps the DVD player and the connection used at the time. so lets hold the personal comments eh?

Chris

*white flag*
 

LV426

Administrator
Staff member
I'm sorry.

Let me put it another way.

LCDs don't produce a rainbow effect. At all.
 

rob12770

Banned
No Lcd's dont, I have notice this phenomenon on crt, but I would not call it a rainbow effect, I have noticed its worse if the convergance is not right, thus I have come to the conclusion that is all it is, when properly converged I cannot see it even if if i scan quickly accrosss the screen. suggest this topic be closed.
 

Nebby

Novice Member
Hi rob12770

This is just what I wanted to hear! I can't look at some dlp's for more than a minute or so, before pretty patterns start to appear before my eyes. Never had the problem with my Mitsubishi lcd...just a naff picture. If what you're suggesting is that my crt "rainbow" problem is due to how I've set the pj up, then I'll be a very happy bunny! Guess it's just a case of try and try again...

To confirm, when you say 'properly converged', you mean the red, green and blue tubes should sit perfectly, one on top of the other, don't you...not just 'hidden' behind the green?
 
R

rob_w

Guest
Originally posted by rob12770
No Lcd's dont, I have notice this phenomenon on crt, but I would not call it a rainbow effect, I have noticed its worse if the convergance is not right, thus I have come to the conclusion that is all it is, when properly converged I cannot see it even if if i scan quickly accrosss the screen. suggest this topic be closed.

Just because you've decided that its bad convergence that causes it doesn't really close the topic. I for one would love to know if more people see this on crt's.., and whether they all have badly set up projectors.:confused:

Cheers
Rob
 

LV426

Administrator
Staff member
When I said I'd seen the effect, the first time, it was on a high-end piece of equipment which had been specifically set up to show it at its best - at the first 'Event' in Glasgow. Those who know what I mean by 'Event' will know that the projectors there were all giving of their absolute best. So - yes, they were converged exactly right. I can't tell you exactly what equipment was in use, but I'm pretty sure it was about as good as it gets.

The next time I saw the effect was at a show at the Renaissance in Manchester in 2002?. The Denon room had, in it, TWO Barco CRTs plus associated scalers and so on - those more directly involved will say what - and, again, had been set up by real experts in the field. Again, they were (all 6 images) converged right.

On this occasion - on this VERY forum - several others also commented that they had seen rainbows.

I may be wrong, but, perhaps the common factor in these two experiences is that, in both cases, the screen was very large in relation to viewing distance - exactly how Home Cinema should be.
 
R

rob_w

Guest
""I just dont see the point in bitching at each other ?""

Fair enough, ain't all of us bitching though;)

Rob
 

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