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It's been said that you could kludge a regular photographic meter IF it has a narow enough field of view. You'd have to compare it against a "regular" light meter then determine a "fudge" factor. (1) Not very convenient, having to take a reading then multiply or divide by some number all the time. (2) You have to have a "regular" meter to compate with in the first place, meaning you have to either buy one or know someone who would let you borrow theirs. -- Why not just borrow it and use THAT?!

PS: Mr. Pytlak is the expert on this. He wrote an article in Film Notes. Ninety percent of what I know comes from reading that article. I forget what issue it was, but I bet it's on the Manual Downlads page.

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The Minolta LS-100 and the SpectraCine CineSpot SC-600 were specifically designed to measure screen luminance. The UltraStereo Labs PSA-200 Projection System Analyzer is really handy, since it looks at the entire screen at once, and allows you to see the effect of any lamphouse alignment changes on uniformity using a laptop computer display.

Using a less expensive spot photometer to measure light is an option, but it needs to be calibrated to read correctly for xenon light, and the 48 interruptions per second of the shutter. Many photographic meters are only accurate to within 1/3 of a stop, which is not enough to tell the difference between 12 and 16 footlamberts, but if properly calibrated, they are better than not measuring at all.

One idea is to purchase a Minolta LS-100, SpectraCine SC-600, USL PSA-200, or similar "real" screen luminance meter, and SHARE it among several theatres in a city. A $3000 meter to properly set up and maintain 50 or 60 screens is certainly a worthwhile investment in quality. With reasonable care, these meters will last for many years.

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Forum/Archive

10-12 footlamberts
Christopher Seo
11-12-1999
and scroll down a ways you will find a chart which you can use to convert the units of measurement found on many spot meters, to Footlamberts. I used to use a Soligor spot meter until I got fancy and bought the Spectra. I found them to be very close. It was just a pain in the posterior to have to take a reading and then go to the chart and then back . . . . . . . . . . . .

You're correct that having to consult a conversion table between Exposure Value (EV) and footlamberts is a real pain.

Here's your meter's table:

EV 7 = 5.2276 footlamberts
EV 8 = 10.455 footlamberts
EV 9 = 20.91 footlamberts
EV 10 = 41.821 footlamberts

Looking at the conversion table, it's easy to see that these meters have considerable compression of the scale. As I noted, reading most of these photographic spotmeters closer than 1/3 of a stop (EV value) is difficult, and 1/3 of a stop (EV) separates each of these footlambert values:

4
5
6.25
8
10
12.5
16
20
25
32

(Standard SMPTE 196M specifies an aim of 16 footlamberts (55 candelas/square metre), and an allowed range for theatres of 12 to 22 footlamberts).

I agree using ANY properly calibrated spotmeter is better than using NO meter.

As I suggested, perhaps a few theatres in each city could get together to purchase and SHARE a "real" calibrated screen luminance meter that reads directly in footlamberts (or candelas per square metre), and circulate it for a weekly check of screen luminance of all the screens in each theatre. Dare I say COOPERATE with each other to improve quality?

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

Since SpectraCine is in Burbank CA, where you are located, why not go there in person? You can probably talk to the technician doing the calibration. Show them the discrepancies in person.

FACTORY SERVICE CENTER
SPECTRA CINE RESEARCH, CORPORATION
3605 W. Magnolia Blvd
Burbank, CA 91505

Jose A. Najar- Service Manager
Tel: 818 954 9222
Fax: 818 954 0016
http://www.spectracine.com/repair.htm

Proper calibration does require an optical bench and "standard" light source, or at least a "reference" meter traceable to NIST or ISO standards.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

I have gone that avenue and thus I have given up on Spectra to calibrate my light meters. I have spoken to them personally and they are of no help what so ever. IF you have ever been there in person, the building is located i a small office complex that looks like it should be a dentists office. The front room where you are attended to is so small one client can barely fit inside at a time. The place is very disorganized and the people there are discourteous and rush you while trying to get business and questions answered. I have had nothing but bad luck in the three years dealing with them and am looking for another company or some sort of self-calibrating advice.

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The USL website has more information, including the SMPTE paper about the PSA presented by Roger Hibbard and Jack Cashin:
http://www.uslinc.com/

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

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