CurtPalme.com Home Theater Forum

Melifluonze · Posted: Sat Nov 08, 2014 1:20 pm Post subject: The color of filters...

Why is it that C elements are red and dye in glycol or H144 lenses seems to be magenta?

Also, what should the filter wavelengths or specifications be for red and green on 8" P16 and/or 180 tubes?

- M

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

I'm not sure about the dyed glycol, but as I saw my the colored lenses (HD-6, HD145) all looked the same 'red' as the c-elements and not magenta. There isn't much type of phosphors are used in projection tubes, by the way the last three letters designating the used phosphor int the panasonic nomenclature,
BMB is for blue, HKA for green (standard), RJA for red, tubes ending with these codes are have the same phosphors regardless of size, focusing type or pinout.

cosaw · Posted: Sat Nov 08, 2014 4:00 pm Post subject:

I think it's just slightly different ways of doing the same thing. Please someone correct me if I've got this wrong but I get the feeling it's more the Sony tubes that use Cyan and Magenta filtering?

I looked up some subtractive colour mixing theory: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/filter.html

As far as I understand we're essentially trying to block yellow. Discussing Magenta and Cyan filtered tubes again and using the theory in the link above, I guess that:

The red tube is putting out too much green. As red and green make yellow then if we block the green component we will only allow red through the filter and yellow won't be created. For this we use a Magenta filter.

The green tube is putting out too much red. As green and red make yellow then if we block the red component we will only allow green through the filter and yellow won't be created. For this we use a Cyan filter.

The blue tube must be fairly pure and so not need a filter.

Now all we need is someone to explain filters that are not Magenta or Cyan.

Again, someone correct me if I'm wrong but it seems more red tubes that seem to follow different rules when it comes to the C - element. Anyway we have to remember that Red, on the face of it, seems close to Magenta. Also whatever colour a filter appears to be - is surely the colour it is intended to allow to pass. So a red filter allows red and blocks everything else. Maybe you pick the methodology based on what type of phosphor your using as gjaky appears to suggest.

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

cosaw · Posted: Sat Nov 08, 2014 4:29 pm Post subject:

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

cosaw · Posted: Sat Nov 08, 2014 7:53 pm Post subject:

Can't really say I completely understand the graph or what it represents exactly. Suppose it's worth noting that red is all over the place whereas the crossover between blue and green is far more well defined.

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

cosaw · Posted: Sat Nov 08, 2014 10:23 pm Post subject:

So is the darker green C-element intended to block more blue or something else? If it's just darker as opposed to a different green then surely all it will do is cut overall light output relatively equally across the whole spectrum.

Melifluonze · Posted: Sun Nov 09, 2014 4:47 am Post subject:

Thank you for all the info, folks!

Very informative!

- M