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AnalogRocks
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Joined: 08 Mar 2006
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Location: Toronto, Ontario, Canada
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 Link Posted: Tue Dec 29, 2020 6:28 am Post subject: |
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Yeah the bulbs. I've read the stuff you wear for changing bulbs is the top of a bomb disposal officers suite. There are Youtube video's that show what the bulb can do.
IMAX bulb change out: https://www.youtube.com/watch?v=lSIhnR5QzYs
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CIR Engineering
Joined: 25 Aug 2008
Posts: 4264
Location: Chicago USA & Berlin Germany
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| Link Posted: Wed Dec 30, 2020 4:27 pm Post subject: |
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| AnalogRocks wrote: | Yeah the bulbs. I've read the stuff you wear for changing bulbs is the top of a bomb disposal officers suite. There are Youtube video's that show what the bulb can do.
IMAX bulb change out: https://www.youtube.com/watch?v=lSIhnR5QzYs |
And it only lasts 1,200 hours!
craigr
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Zebra
Joined: 02 Jul 2020
Posts: 87
Location: NJ USA
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| Link Posted: Tue Jan 05, 2021 6:44 pm Post subject: |
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| garyfritz wrote: | The docs claim the Eidophor was 80x brighter than CRTs of the day. Other docs claim 10,000 lumens, and I assume that would be ANSI lumens -- I doubt it was current-limited like CRTs are. A 9500LC puts out about 260 ANSI lumens, so 10,000 / 260 = 38x; a G90 at 60Hz is rated 280 lumens, 10000/280 = 35.7. So the Eidophor had roughly 35-40x the lumens of the best CRTs.
They claimed screens up to 18 metres = 59' in width. Assuming a 4x3 aspect ratio, that's 59 * 59/1.33 = 2611 sq ft -- call it 2500 sq ft. So that enormous screen would only have 10000 / 2500 = 4 ft-candles -- unwatchably dim in my opinion. Cut the screen size in half (9 metres = 30' wide) and you'd have a nice bright 16 ftC image. It could probably do an acceptable image 35 or even 40' wide.
Your HT screen is probably about 7-8' wide. Mine is 7.1' x 4', which is 28.4 sq ft. But the Eidophor probably had a 4x3 panel image, and my screen wouldn't use all of the height. A 16x9 screen would only use 9/12 = 75% of the 4x3 = 16x12 panel image. So it would only see 75% of the 10,000 lumens, or 7500 lumens. Which would be really bright, but your screen shouldn't catch fire. 7500 lumens is "only" 5.8x more than the 1300 ANSI lumens put out by my RS-45. My ftC calculations aren't working right -- I'm getting crazy-high ftC for both my RS-45 and the Eidophor -- but it should be about 5.8x brighter than my RS-45, or about 90-100 ftC. I think you could almost watch that in full sun.  |
What period does "CRT projectors of the day" cover? It seems like that device predates CRT projectors. There's a big difference between CRT projectors 1979 and CRT projectors 2001.
I'm not sure I'd believe that thing could match 80 stacked Sony G90 or Barco 909s. Maybe one of those old 200 lumen 480i only analog devices from the early 80's.
It also doesn't really state how "80x brighter" is measured. Most projector manufacturers (including CRT) advertise peak lumens. The marketing literature for a Sony G90 claims over 1000 lumens. Why would we assume the Eidophor documentation would be using more honest metrics like calibrated lumens.
I wouldn't base any assumptions on our more recent expectations for brightness to screen size ratios. Projectors were hysterically a lot dimmer. It's why they started using silver screens in theaters.
We'd probably be horrified by how dim old theater projectors were if we measured what what used to light a 25 meter screen back in the 60's and 70's.
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kal
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