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Topic: kw and Lumens

Philip Borgnes
Film Handler

Posts: 18
From: Seattle, WA, USA
Registered: Apr 2004

posted 05-24-2005 12:27 PM

John, you are a fount of knowledge!

This is a hoot,

quote:
"For comparison, an 1860 Oil lamp with a single flame produces approximately 2,500 lumens"

Now I just need to keep an oil-lamp on hand or two to back up my projector!

Steve, you raise an interesting point about something I just learned about - the difference between off-to-on contrast at the projector (typically the 2000:1 you see on specs) and the ANSI contrast (measured at the screen) which is more in line with your experience of seeing a 450:1 to 600:1. Environment plays heavily into ANSI contrast and is perhaps a more valid measure.

It seems this topic has wandered off a bit of the relation of kw to lumens, but it points out to me at least the need for SMPTE to help us out on this issue.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 05-24-2005 12:55 PM

Obviously, your quote from that source is likely a typo. I suspect an oil lamp produced only a few lumens.

My usual test of contrast ratio is to cast "shadow puppets" in the darkest areas of the picture, like a night scene. A distinct shadow in what should be a black area says the contrast ratio is mediocre.

I remember the comments about how truly black the dark areas of the Kodak VISION Premier Color Print Film 2393 prints were for "Minority Report":

http://www.film-tech.com/ubb/f4/t000334/p2.html

quote:
This was the 2nd time for me. An outstanding effort by Spielberg. The main thing I want to mention though is image quality. Aaron Haney said: "Also, the print that I saw had amazing contrast. There was a "feature presentation" snipe which ended with a fade to black just before the actual movie started. When the cut to the real movie happened, I couldn't believe just how much darker the screen suddenly became. That continued throughout the whole movie. Very deep blacks."

The print I saw today was exactly as Aaron describes. When the black leader of the feature started, it was nearly pitch black dark in the theater -- I actually thought the xenon had blown or something, the screen was so dark. Well, the entire movie was like that - incredible contrast, and very deep, rich blacks. I don't think I've ever seen anything like this before. And no, the screen is not under-lit. There was PLENTY of brightness (focus seemed perfect, and the image was steady too).

Long live film.

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Larry Myers
Master Film Handler

Posts: 371
From: Herndon, VA, USA
Registered: Jan 2001

posted 05-24-2005 03:00 PM

Hi

I collect old oil lamps. The reason the whales were almost wiped out is because of all those old oil lamps. Whale oil burns very bright. I am not sure if it's 2500 lumens but it might be 250 lumens or 250 foot candles or the same as burning 250 bees wax candles at 1 foot away.

USG standard light level in a work place should be about 12 foot candles. A 250 foot candle oil lamp would give off 16 foot candles at 4 feet away. That's 250fc at 1 ft, 64fc at 2 ft, 16fc at 4 ft and 4fc at 8 ft. These old lamps worked very well although, with just plain jane oil, light output is now only about 1/2 of the old days.

Larry

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 05-24-2005 05:48 PM

One of the things that is has been in the works is a uniform contrast ratio measurment target that could be used for film and video...it currently is looking like a modified checkerboard pattern of black and white squares. It is modified so a phometer can fully real the black and white sections and to actually excite such things as lens flare, which really do lower the contrast ratio.

Note too, in a theatre, ultimately the limiting factor will be the ambient light of the theatre itself in order to provide safe visible exits and pathways to those exits.

But back to the contrast test pattern...I'd be quite surprised if any DLP projector even approached 1000:1 in contrast ratio even in a pure pitch black room. It is one thing to basically lens-cap the projector for one reading, and then measure the direct light and say I have a bazillion to one contrast ratio, it is another thing to put up both black and white targets and do the same thing. Panasonic, for one is boasting a 4000:1 contrast ratio...how do they do it? With a variable iris on the light source...that works on all on/all off...but it doesn't work for all on, AND, all off.

If the film people used similar measurement methods...we would take a light reading with the shutter open and then with the shutter closed...it would be a meaningless number...just like the current video CR numbers.

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