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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Tue Aug 29, 2017 2:37 pm Post subject: Help me understand how a screenshot test can confirm FL |
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I've been in a discussion with someone who's been trying to tell me they can determine the light output of my projector using the screenshots and the number from the camera. Other than when I first heard Trump had become president, this tops the list a the most stupid thing I've heard in awhile.
My opinion on this is that it's not possible period.
What's your thoughts on this?
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cmjohnson
Joined: 03 Apr 2006
Posts: 5180
Location: Buried under G90s
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| Posted: Tue Aug 29, 2017 3:15 pm Post subject: |
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It might be possible with a series of calibrations, measurements, and correlations, under laboratory conditions.
If you took reference images of a known calibrated light source and started correlating the image outputs, you could
establish a luminance transfer characteristic for the camera and lens system. But you'd have to do it for all combinations
of shutter speed, aperture, and ISO setting, at the very least.
But short of that, I would never trust any claim that a screen shot confirms light intensity levels.
Anyone who's making that claim and can't produce full calibration data on his entire measurement system and camera system is full of it.
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garyfritz
Joined: 08 Apr 2006
Posts: 12088
Location: Fort Collins, CO
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| Posted: Tue Aug 29, 2017 3:20 pm Post subject: |
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CJ, I think you omitted the "sh" at the start of that last word. 
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cmjohnson
Joined: 03 Apr 2006
Posts: 5180
Location: Buried under G90s
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| Posted: Tue Aug 29, 2017 3:34 pm Post subject: |
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Only because the board filter would have done something about it anyway!
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jbmeyer13
Joined: 03 Dec 2010
Posts: 1135
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| Posted: Tue Aug 29, 2017 4:34 pm Post subject: Re: Help me understand how a screenshot test can confirm FL |
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| mp20748 wrote: | I've been in a discussion with someone who's been trying to tell me they can determine the light output of my projector using the screenshots and the number from the camera. Other than when I first heard Trump had become president, this tops the list a the most stupid thing I've heard in awhile.
My opinion on this is that it's not possible period.
What's your thoughts on this? |
Are they saying they can tell you precisely how many ft. lamberts your pumping out based on the aperture/speed settings of the camera or just an approximation of light output?
The f-stop alone can drastically alter the appearance of the light output on screen so with the rest being equal makes this a pointless exercise if precision is of any importance in the discussion.
C'mon we all know with those Lugs your pushing 3 ftl 
_________________
Projector: Modded 9501LC ULtra- MP VIM, Vold VNB, ETECH LVPS, Silver VIM Cables, HD10F's & a V1 case!
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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Tue Aug 29, 2017 5:01 pm Post subject: Re: Help me understand how a screenshot test can confirm FL |
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| jbmeyer13 wrote: |
C'mon we all know with those Lugs your pushing 3 ftl |
Yes yes.. I was also told that wasn't an exact, but it would be close..
Sounds like this could be Crystal Ball Technology.
Yeah, you would need some of this for sure:
From CJ:
| Quote: | | It might be possible with a series of calibrations, measurements, and correlations, under laboratory conditions |
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cmjohnson
Joined: 03 Apr 2006
Posts: 5180
Location: Buried under G90s
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| Posted: Tue Aug 29, 2017 6:29 pm Post subject: |
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LUGs will easily achieve 11 ft-L but maybe not when focused to ultimate sharpness.
When I did that simulator retubing job in Japan, there were options for "high" and "low" brightness calibrations,
and the customer specified the low calibration.
That meant the projectors were all calibrated to deliver a whopping, eye-searing 3 ft-l peak white into the rear projection screens,
as seen from the pilot's position inside the dome.
They got pretty good tube life at 3 ft-l, I'll say that!
It was fine for a flight simulator.
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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Tue Aug 29, 2017 7:40 pm Post subject: |
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| cmjohnson wrote: | LUGs will easily achieve 11 ft-L but maybe not when focused to ultimate sharpness.
When I did that simulator retubing job in Japan, there were options for "high" and "low" brightness calibrations,
and the customer specified the low calibration.
That meant the projectors were all calibrated to deliver a whopping, eye-searing 3 ft-l peak white into the rear projection screens,
as seen from the pilot's position inside the dome.
They got pretty good tube life at 3 ft-l, I'll say that!
It was fine for a flight simulator. |
Absolutely, and that is what I've also been saying about LUG's. They can get bright, but any High Resolution CRT design purpose would be for low drive or lower drive. That is how you maintain it's resolution performance. And when used in simulators, the low drive is important to cut back on hot spotting and peaking (clipping) problems.
Ive done quite a bit of them myself, but the best was a setup in New Jersey that was a Cube (Stereo 4 projectors and screens) that showed what it looked like when a jet landed at night on an aircraft carrier. For that setup, they stayed with CRT much longer because the jet was landing in darkness..
Last edited by mp20748 on Wed Aug 30, 2017 8:03 am; edited 1 time in total
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cmjohnson
Joined: 03 Apr 2006
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