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Topic: 16mm Screen Illumination (Calculation of)
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 03-20-2006 06:08 PM
Dear Prick...err Manny...
Illumination is illumination. That is, lumen output to a square area of screen is the same for all projected formats but John P hit the nail on the head. When was the last time you saw a lumen output for a 35mm projection system? As such, there is no point of reference. Many people are working with the 12xH^2 for 35mm 1.85 and that works to some degree and does get you into the ballpark (depending on lens, screen and lamphouse system). Many systems are better served with 13*h^2 for 35mm 1.85.
But back to 16mm...all is not so easy. 16mm is an efficient format in that it is nearly square...well 4:3. However, the smaller aperture requires an arc with a smaller point of light for efficientcy (it is only .286" high). With 35mm, most lenses are effectively f/2.0...16mm lenses are all over the place.
I've seen such lumen ratings on ELMO xenon projectors as 5500 lumens for 2KW, 3500 Lumens for 1KW, 2000 Lumens for 550W, and 1400 lumens on 350W. These are all with 50mm f/1.2 lenses so you lumen output will most likely go down from there.
If you don't have a xenon lamp, then the color temp is going to look a bit orange which will throw off your intuition on brightness.
So, using these numbers and presumming a matte-white screen and a brand new lamp and everything going your way....etc.
A 350 xenon projector is good up to about 8 x 10.5
A 550 xenon is good up to about 9.5 x 12.75
A 1000 xenon is good up to about 12.75 x 17
A 2000 xenon is good up to about 16 x 21.25
For what ever its worth...it seems like I always end up with a lens in the 35mm EF range so that takes about a 20% hit due to the less efficient lens (they tend to be closer to f/1.5).
Now the above was for 16fL...you can most likely slide it down closer to 12fL for most shows and it will still look decent (and barely within SMPTE specs).
With the smaller halogen lamp portables...you really should restrict yourself to under 8-foot tall screens but I've seen them do better than they should on larger screens...again, their image will be yellow appearing to begin with then again, depending on how the print was timed (tungsten or white) it will look proper with orange light.
We once did a premier in 16mm with an "EK" print where we told the lab we thought we could get (and we did) 14fL with a given projection system (happened to be a Norelco EL5020 with a Strong Lume-X and Schneider 35mm Cinelux, of course). Since the person that shot the film owned the lab that made the print...we got a perfectly timed and white-point print for the projection system used (you never get this in real life...only when the lab owner's film and premier)...the result was FANTASTIC...I still remember it as beening the best 16mm I've ever seen and it eclipsed virtually all of the 35mm release prints I've ever seen.
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