Quote:
Originally Posted by Username1
Hu- You know there's some funny stuff in yer graphs...... In the "15gp22-21axp22.pdf" that includes "RX43" in the on screen title. The 15gp22 actually has a narrower color spectrum than the 21axp22, and much narrower than p22 phosporous. Smaller triangles on the graph do actually indicate narrower color spectrum. And on the measured graphs both the 15gp, and the 21axp seem to have a very similar shape, except for the brightness level. (You notice in the old RCA p22 graphs also put up on this thread RCA correctly uses the term "relative" in its brightness scale, the vertical left scale. Relative in this case is kind or normalizing with refrence to brightness.) For actual more acurate comparison you are going to have to measure both, or all tubes you compare at very similar brightness levels. (or beam currents, Something I took exception to when this discussion took place many years ago on Pete's private site.) You will get very hard to distinguish readings using those scales with such wide differences in light levels. Think about reading 2V acurately on an analog meter when you chose to use the 400V full scale deflection setting. And you also have to first establish that your instrument has a flat response across the full spectrum. And in addition, that the instrument is accurate across all light intensity levels. And as for the overall screen face color, it may just be the difference in the material between the phosphorous pigment, or in the material used to hold the phosphorous in suspension when deposited on the screen. Anyway just a squirrels thought on the presented data.
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P22 refers to any RGB color tube. The points shown are some particular set of phosphors, which appears to have the later non-NTSC blue. Cliff maybe can tell us the source of the numbers, which may be ideal phosphor numbers or measurements with a colorimeter rather than a spectroradiometer.
The reduced purity in the 15GP22 tube is to be expected. Later techniques for reducing electron scatter, etc. had not been invented yet. Specifically, the green is very close to where it should be, the blue is close to NTSC blue, which is not as violet as later blue phosphors. The only real degradation is in the red, indicating the red purity was not ideal. Also, maybe Cliff can comment on whether these numbers came from a spectroradiometer, or a colorimeter. If a colorimeter, errors are also to be expected.
I talked with the president of Spectracal at the Hollywood Post Alliance in February, and he said that the I-1 spectroradiometer is much more accurate than colorimeters, and is reasonably comparable to much more expensive spectroradiometers. Of course, this non-lab model, costing about 1/10 of the top ones, is only calibrated once, at the factory, whereas a lab instrument would be calibrated yearly or more often to a NIST-traceable standard. The important thing is that it can correctly handle the red primary spectrum that trails off into the infrared. Back when we first measured Cliff's field-sequential color wheels on a CRT with the Spyder II colorimeter, we got wildly wrong results due to the deviation of the deep red response from the standard observer curves. The Spyder III improved that considerably, but only the I-1 gives results that are really close to eyeball color.
05-13-2011, 07:16 AM
Hybrid Mode
