Quote:
Originally Posted by earlyfilm
I've never seen the mention of filter density in the Peter Goldmark system, just the Kodak or Wratten filter color number, and knew that surviving CBS color filters did not match the published Wratten numbers. <<<-->>>
The mention of an overall yellow filter by the author is counterproductive.
James
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I've read this article before and there may be some confusion in the filter number callouts.
The use of a Wratten #6 Yellow filter over the entire screen is correct for an experimental CBS set, the RX-40 color converter, which used two standard Wratten filters and one special one in the wheel. The standard filters are Red Wratten #25, Green Wratten #58 and the special is a Blue Wratten #47, 3/4 density. The yellow filter rebalanced the overall image color from blue-ish to white.
The second filter set was called "Monsanto E" and didn't require the yellow filter.
Both sets of filters made the same color picture, but by different means.
What does all this mean today if you are going to build a color wheel set?
It is absolutely correct, but now useless information because neither sets of filters have been made for the last 50 years.
Wratten filters would also be prohibitively expensive, costing about $2400.00 for enough to build ONE 22-1/2 inch wheel for a 10 inch CRT. [!!!!]
I did a lot of research for the ETF Museum on color filters for their CBS sets and found I could use good quality polycarbonate lighting filters to make new color wheels. The picture quality is excellent and the work I did utilized a good spectroradiometer to document and match the color filters correctly.
The basic requirements for a set of color filters today is that they must produce no difference in, or otherwise 'color' the white light balance from the CRT as they spin in front of the screen, they must be strong and they must not fade.
If you are building a wheel set you might be using one with a round tube 10 or 12 inch CRT. Anything bigger and the wheel becomes VERY LARGE and hard to control.
The color temperature of most 10 and 12 inch CRTs is in the realm of 7000 degrees Kelvin. This is a bright bluish white, especially if you have a 10FP4 or a 12KP4 Aluminized CRT in the set.
Three particular color filters made by Roscolux will color balance very well with these CRTs and produce beautiful, deeply saturated color pictures.
The type numbers for them are Roscolux Red #25, Blue #76 and Green #90.
They are very cheap compared to Wratten Kodak filters, about $8 bucks for a 20X24 inch sheet from any theatrical lighting company.
Building a color wheel is easy to do with standard craft supplies. If you need more information about any of this, I'll be checking the thread.
The usual disclaimer: I have no affiliation with Roscolux or any other manufacturer of color filters except as a happy customer.
Cliff