Film-Tech Forum ARCHIVE: 16mm Screen Illumination (Calculation of)

This is topic 16mm Screen Illumination (Calculation of) in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Manny Knowles (Member # 1171) on 03-20-2006, 11:28 AM:

Can you find it in your hearts to help an insensitive prick???

How do we calculate screen illumination for 16mm?

I'd like to know what the standard says but I'd also like to know how to "ballpark" the requirement (like multiplying sq. ft * 5W for 35mm).

Posted by Jeff Taylor (Member # 443) on 03-20-2006, 02:48 PM:

I'm sure I'm oversimplifying it, but why wouldn't 16mm be the same as 35 in terms of desired screen illumination. The film's the same except narrower, the lenses are similar, so why wouldn't the same formula apply?

Posted by Phil Hill (Member # 371) on 03-20-2006, 02:57 PM:

Manny, knowing you all these years, I've NEVER known you to be insensitive...

Posted by Manny Knowles (Member # 1171) on 03-20-2006, 03:37 PM:

One at a time...

Jeff --> Interesting. In hazarding a guess, I couldn't decide whether it would be the same or about half (around 45%).

Phil --> What're you saying??? That i'm "just" a prick?

Posted by John Pytlak (Member # 331) on 03-20-2006, 03:38 PM:

Standard SMPTE 196M specifies an aim screen luminance of 16 footlamberts for 16mm, just like 35mm.

I suspect the efficiency of illumination for 16mm projectors varies more than 35mm, so I'm not sure there is a "rule of thumb" relating lamp size to light on the screen. If the projector has a specification for total lumens, figure at least 16 lumens needed for each square foot of a matte white screen.

Posted by Steve Guttag (Member # 268) on 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.

Posted by Mike Croaro (Member # 3123) on 03-20-2006, 07:01 PM:

Hi Manny; Folks:

This will give you an idea regarding the 350 watt xenon lamp light oputput. A few years ago I shot a picture 8 X 11 with the Eiki EX-3000 Xenon machine. 350 Watt xenon lamp and 2 inch F/1.2 lens. Picture was very bright. I could have enlarged the screen to say 10 X 14 and still obtained a nice bright picture.

Mike

Posted by Jeff Taylor (Member # 443) on 03-21-2006, 11:15 AM:

A million years ago in Junior High I recall routinely showing films in an 800 seat auditorium with balcony (sorry, can't remember screen size) using an RCA 400 JR with a 1200 watt incandescent lamp (3-bladed shutter!)with decent results. In a pinch we also used DeVry Bantam's with a 1000 watt lamp. Given the lamps, reflectors, and optics of the day I doubt those machines put out more than the 800-850 lumens that table top 250 watt halogen 16mm projectors claim today.

Posted by Steve Guttag (Member # 268) on 03-22-2006, 03:43 AM:

You'll probably be down to 10-10.5 fL with a 350-watt xenon on a 10-foot tall picture...at 8-feet it should have been around 16fL with 12fL coming in around 9.25-feet tall.

Posted by Manny Knowles (Member # 1171) on 03-25-2006, 04:40 PM:

Gee, thanks guys!