Film-Tech Forum ARCHIVE: 10-12 footlamberts

This is topic 10-12 footlamberts in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Brad Miller (Member # 2) on 11-12-1999, 03:50 AM:

Seems someone listened to Gordon's recommendation as the prints of Messenger are to be projected between 10-12 footlamberts.

What does everyone think of the projected image? Did anyone who normally ran 16 footlamberts actually lower their lamphouse output to meet the 10-12 footlambert spec?

Posted by John Pytlak (Member # 331) on 11-12-1999, 06:57 AM:

Standard SMPTE 196M specifies an aim of 16 footlamberts, with an allowed range of 12 to 22 footlamberts for theatres. Almost all prints are timed by the laboratory in accordance with this standard, and should ideally be projected at 16 footlamberts. The contrast aims of the film stocks are based on prints being shown at the 16 footlambert aim.

If the distributor timed the prints lighter in hopes of compensating for theatres that had dim screens, they compromised the overall quality of the image. Making a print lighter will tend to compress the highlight detail, wash out the flesh tones, and make the blacks more "smoky". But since they accepted the "look" of the prints that way, and are recommending a lower luminance for showing them, I would comply with their request. But be sure to return to the standard 16fL luminance after the run.

To show why this philosophy is flawed, imagine taking the practice to the extreme. If theatres have dim screens, why not make the prints REALLY light? If you do, the film will be clear and have no image!

------------------
John Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Research Labs, Building 69, Room 7419
Eastman Kodak Company
Rochester, NY 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243

Posted by John Walsh (Member # 168) on 11-12-1999, 10:50 AM:

I really hate to sound like a cynic (and maybe like a pain in the ass, too) but I just can't see 99% of theaters adjusting the lamp to match the recommened fL for one film. IMSO (in my sarcastic opinion) most theaters can't even get 10fL if they wanted to. Sorry to rant, but not only do I feel this is the most prevalent single problem in theaters, but is ignored by owners and equipment installers.

Theater owner: I need 20 consoles for my new theater complex. I want the best light on the screen I can get. All of them are 18ft x 45ft.

Equipment supplier: "Well, our "BlastLight 5000W" seems about right. That'll be $1800 each."

Theater owner: "At DarkStar supply, they told me that the Cataract 2000W's would work. It's $750 cheaper. See ya later....."

Equipment supplier: "Wait! I can supply the TotalEclipse 2000W's," (sigh) "for the same price."

Theater owner: "How good are they?"

Equipment supplier: "Well, they aren't as bright as....."

Theater owner: "Well, if they're no good..." (starts dialing cell phone.)

Equipment supplier: "I meant, uhm.. ah.. the PAINT on the outside is not as bright, yeah, that's what I meant..."

Theater owner: (Hangs up cell phone, but doesn't put it away.) "So I really don't need 5000 watts?"

Equipment supplier: (Eyes are on phone) "No, you don't really need it."

Theater owner: "OK then." (puts phone in pocket.) "Trying to up sell me, eh? Ha-ha, well, I'm an expert at that. So how good are these lamps?"

Equipment supplier: (Sighs) "Very good." (theater owner reaches towards pocket) "I meant to say, 'the best you can get.'"

Theater owner: "Good, that's what I want to brag to other owners at NATO. Give me some free logo T-shirts and baseball caps, too. Those consoles come with the bulbs, right?"

It also doesn't help that you need a $2200 meter to read brightness. When you can't get your boss to buy good quality splicing tape, how are you going to get a meter? Unless someone comes up with a cheaper way of mesuring reflected light, few people will even know how bad off they are.

SO THERE!
.....i feel better now.....

Posted by Brad Miller (Member # 2) on 11-12-1999, 02:46 PM:

Comical post...but all too true, John. I think you are correct that if 1 in 100 theatres actually adjust their lamp output to meet this temporary spec, the director will be lucky!

I haven't screened this film, but will make a point to check it. It is playing in an auditorium with an 80 foot screen and a 4.5K lamp, which can only get 12fl anyway...so that was easy. Once it moves to a smaller house though, 16fl is effortless to achieve on scope! That's when the timing will really show up if the bulb isn't defocused a bit.

Posted by Steve Guttag (Member # 268) on 11-12-1999, 03:10 PM:

Excellent Post!!! It is often too true. Especially the one about the other dealer that ALWAYS has a cheaper alternative that they have put in 1000s of theatres with "no complaints."

Hey with a 12fL requirement, most theatres should be about right...it is the 16fL that they have problems with!

Steve

Posted by Randy Stankey (Member # 64) on 11-12-1999, 03:37 PM:

I'm not adjusting our lamphouses. No way! CFS's are a pain to adjust. On top of that, the print is going to move in two weeks and then the week after that, etc. etc.... Adjusting the output up and down on several projectors would be crazy even IF i had time to do it!

Even if I had something like the Stong P.S. I STILL wouldn't do it. It's silly!

Posted by Christopher Seo (Member # 7) on 11-12-1999, 04:47 PM:

Regarding the measurement of screen brightness... does anyone know if light meters used in photography can be adapted to fit the bill? I know there are two different kinds of measures, one for incident and one for reflected light... can one of these be used?

Posted by Steve Guttag (Member # 268) on 11-12-1999, 06:17 PM:

You have actually answered your own question, no a photography light meter won't do it becuase it will read in foot-candles. Furthermore it's sensor is designed for light to fall upon it rather than focus it's sensor onto a specific part of the screen. Now if you use you meter in conjunction with a light meter you can measure screen gain!

Steve

Posted by Gordon McLeod (Member # 33) on 11-12-1999, 06:48 PM:

actually most spotmeters can read footlamberts but must be recalibrated to alow for the ballistic action of the shutter
Pentax is a favorite to get converted

Posted by Ken Layton (Member # 133) on 11-13-1999, 01:58 AM:

The manual for the Strong "Utility" carbon arc states it can put out 20 foot lamberts on an 18 foot wide screen.

Posted by John Walsh (Member # 168) on 11-13-1999, 01:54 PM:

Yeah, but I think that's just a hyped-up claim. There are other factors besides screen size which effect the final brightness. It's like cars in the '60's; back then, listed engine horsepower was on a dynamometer; today it's at the wheeles with all accys. on and running.
Not that a Strong was a POS, but that everybody hyped their spec's.

Posted by John Pytlak (Member # 331) on 11-23-1999, 10:32 AM:

Based on Strong's "Lens Selector and Picture Size Computer", figure about 5 watts per square foot of screen area (2.39:1 scope format) to adequately light a 1.0 gain matte white screen. So a 1000 square-foot matte screen will need at least 5000 watts.

With a 1.5 gain curved screen, figure about 4 watts per square foot. And about 3 watts per square foot for a 1.7 gain curved screen.

Obviously this assumes normal efficiencies for the lamphouse, shutter and optics. Any misalignment, dirty screen, three-blade shutter, etc. will require much more power. The effective f/stop of the projection lens is also an important factor, with a wider lens opening offering greater light efficiency, at the expense of depth of focus.

BTW, a 1000-square foot screen is 20.5 X 49 feet for the 2.39:1 scope format.

Posted by John Pytlak (Member # 331) on 11-23-1999, 10:53 AM:

Just an addendum for our friends outside of the USA that use the metric system:

For a 1.0 gain matte white screen, figure about 54 watts per square metre of screen area. So a 100 square metre (6.5 X 15.5 metres) matte white screen needs at least 5400 watts, so a 6000-watt xenon bulb is the smallest that will do the job.

Use at least 43 watts per square metre for a 1.5 gain curved screen.

Use at least 34 watts per square metre for a 1.7 gain curved screen.

Again, these "rules of thumb" are based on the Strong/IscoOptic "Lens Selector and Picture Size Comparator".

Posted by John Walsh (Member # 168) on 11-23-1999, 02:31 PM:

I always used:

Height of screen squared, times 12

exp: 20.5 ft screen sq = 420.25
times 12 = 5049 watts

Which is the same, but JP's formula is better, because you can account for gain screens (which our theater company dislikes, so we don't have to worry about it.)

Posted by Bill Purdy (Member # 202) on 11-29-1999, 04:06 PM:

Returning to the question of how you can measure the brightness, I offer a suggestion. Back in the early 80's when the THX program was beginning, they still hired outside technicians (not employees of the theatre) for the re-certifications and the TAP checks. We had the problem that there were no good meters available unless you found an old Spectra or the like. In my case, I bought a used Soligor spot meter which came with a handy chart for converting the EV readings into Ft. Lamberts. It was a little tricky because the part of the scale of interest to me was very compressed. After taking a reading I had to consult the little chart taped to the side of the meter, but it worked. When Spectra brought out their new model I was pleased to discover that my old one method was really quite accurate. The key is that you use a spot meter which is calibrated in EV.

Posted by Vernon Klingman (Member # 258) on 12-11-1999, 06:57 AM:

Sometimes even foot lambert meters don't work right. Take a look at my news letter about the Sekonic 508C foot lambert meter.
http://www.cin-tronics.com/News_letter.htm

------------------
Vernon Klingman
Cin-Tronics
http://www.cin-tronics.com

Posted by Chris Erwin (Member # 176) on 12-11-1999, 08:21 PM:

After reading this post again, I felt the need to comment. If the standard is set, in this case around (16 foot lamberts), and someone decides in thier own infiniate wisdom to time the release prints funny,that's their problem. I wouldn't screw with my xenon because someone choose to be "artisy" or "creative".

Just IMSO
--Chris