Black Widow Ultra with other Base Paints? - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 16 Old 06-04-14, 05:25 AM Thread Starter
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Re: Black Widow Ultra with other Base Paints?

Now I'm utterly confused. A direct measurement with the colorimeter (with a diffuser) aimed at the projector gives me a reading of 19.3 ft-L. Bounced off the white wall, this drops significantly to about 10.4 ft-L. Is it even possible to have a gain of 0.54 with a white wall??

Just to make sure that the diffusion wasn't throwing off the readings, I put a piece of white paper (yeah, I know it's not exactly spectrally neutral) in front of the colorimeter. This time the light was severely attenuated since I was using thick paper. Even so, the calculated gain was 0.52 for this run.

In both cases, color readings were fine. RGB was balanced and I even took measurements of my primaries and secondaries and nothing really seemed off - just the light intensity. If these readings are correct, then that would mean that my projector is tossing ~52 ft-L of light at that distance. Way higher than ProjectorCentral's calculated 29 ft-L. Right now I'm inclined to believe that my measurements are just off since I'm not using a unity gain reference but I'm open to ideas as well. I'm not all too confident if I can find some of that magnesium carbonate stuff, though. I've tried checking out our local online advertising sites and I found none of it.
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post #12 of 16 Old 06-04-14, 04:16 PM
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Re: Black Widow Ultra with other Base Paints?

Yeah, a white piece of paper would not have a gain that low; or a bright white paint either. Something is wrong somewhere. Now that I think more about it I'm going to have to say that I don't think a colorimeter can take reliable gain readings, it's just not designed for doing that. In order to get accurate gain readings one needs to have a 1° spotmeter. A colorimeter has a much wider field of view when taking readings. It may be possible to get something like a gain reading, but it would not really be comparable to true gain readings because it would be reading a much larger "spot" on the screen.
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post #13 of 16 Old 06-04-14, 04:33 PM Thread Starter
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Re: Black Widow Ultra with other Base Paints?

In that case, should I take safer path and go with a lighter gray (Veil) as opposed to the darker one (Dover Grey)? I would think that a slightly brighter screen is easier to fix than a dim one right?
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post #14 of 16 Old 06-04-14, 11:25 PM
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Re: Black Widow Ultra with other Base Paints?

Quote:
nightsky87 wrote: View Post
In that case, should I take safer path and go with a lighter gray (Veil) as opposed to the darker one (Dover Grey)? I would think that a slightly brighter screen is easier to fix than a dim one right?
I'm not quite sure what you mean by "fix". I can tell you one thing that might help you is that while the shade difference between 'Dover Grey' and 'Veil' is visible, it is not a "night and day" difference. We have found during testing of neutral gray screens that it takes a N0.2 difference (such as N8 and N8.2) to even be visible when the screens are side-by-side!

I guess it would be safer to get the lighter gray paint for your screen since you can usually turn down the brightness of the PJ if that is needed, but you can't make it brighter if it's already at maximum brightness.
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post #15 of 16 Old 06-05-14, 12:12 AM Thread Starter
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Re: Black Widow Ultra with other Base Paints?

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Harpmaker wrote: View Post
I guess it would be safer to get the lighter gray paint for your screen since you can usually turn down the brightness of the PJ if that is needed, but you can't make it brighter if it's already at maximum brightness.
Yep, that's what I was referring to by an easy "fix". I could turn down the lamp power from SmartEco to Eco if the image is far too bright. I'll probably just lose some ambient light suppression with the lighter paint. I guess I'll just have to try it out!

Thanks again for the help! I'll try to report back once that project is underway.
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post #16 of 16 Old 06-06-14, 04:51 PM
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Re: Black Widow Ultra with other Base Paints?

Quote:
nightsky87 wrote: View Post
Now I'm utterly confused. A direct measurement with the colorimeter (with a diffuser) aimed at the projector gives me a reading of 19.3 ft-L. Bounced off the white wall, this drops significantly to about 10.4 ft-L. Is it even possible to have a gain of 0.54 with a white wall??
Yep, there's something wrong here and probably is the way of measuring...

I suppose you aimed the projector from great distance with your colorimeter meanwhile you took your off screen readings from 30-40 cm away from your screen, right?

Well, all sensors have a range of reading...practically is a diameter that opens and closes as you get near or far from your light source. Take a look of this diagram and you 'll understand what i am talking about:




Therefore, i think that you take your off lens readings from a distance far more longer than one that took off your screen widing the angle and consequently reading more light.

Hope to be a bit clear because i don't believe i explained it well...sorry.
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