Film-Tech Forum ARCHIVE: What is everyone using for a light meter !

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Posted by Alan Gouger (Member # 543) on 11-26-2000, 09:34 PM:

Is there anything out there thats cost effective that works without costing $$$$$

Posted by Randy Stankey (Member # 64) on 11-26-2000, 10:47 PM:

Cheapest one I've seen costs about $1,800 to $2,000!

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.

Posted by Gordon McLeod (Member # 33) on 11-27-2000, 07:04 AM:

Most analogue meters will work as the mechanical movement of the meter will null the shutter flicker.
Digital ones must have sufficient sampling rates to null out the shutter effect
A spot meter with 1 degree sensing will work is it meets the above requirement
Even though the mechanical ones will average the shutter they must be recalibrated for it
Pentax analogue ones are recalibratable.
The most popular is the Minolta LS100 or the Spectra Cine

Posted by John Pytlak (Member # 331) on 11-27-2000, 08:38 AM:

Here are the two recent Cinema Notes articles I wrote about measuring screen luminance:
http://www.kodak.com/US/en/motion/newsletters/notes/march2000/pytlak.shtml
http://www.kodak.com/US/en/motion/newsletters/notes/june2000/pytlak.shtml

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.

------------------
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

Posted by Alan Gouger (Member # 543) on 11-27-2000, 09:10 PM:

Thanks everyone.
John: great articals!

Posted by Bill Purdy (Member # 202) on 11-28-2000, 09:32 AM:

If you will go back in the archives to:

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 . . . . . . . . . . . .

------------------
Bill Purdy
Component Engineering

Posted by John Pytlak (Member # 331) on 11-28-2000, 12:09 PM:

Thanks, Bill:

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?

Posted by Rory Burke (Member # 512) on 11-28-2000, 12:39 PM:

THe Spectra CineSPot is probably the best way to go as far as reliability and accuracy...and cost being the main issue. However the meter must be calibrated or forget accuracy. My problem is I have sent in several CineSpot meters back to Spectra for a pricy calibration and to have them come back all reading different values. I have given up on calibrating with them totally. Is there a another way or another company that can calibrate them? Is using a fancy laptop lightmeter like the Ultra Stereo and then calibrating each one of my Cine Spot meters< it should be only a little trim pot or something to adjust only> a safe route to go? Or do I have to actually risk again the $200 bucks for some kid behind the counter to do a fair and precise job for me?

Rory

Posted by John Pytlak (Member # 331) on 11-28-2000, 01:19 PM:

Rory:

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.

Posted by Rory Burke (Member # 512) on 11-28-2000, 05:25 PM:

John P.

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.

Rory

Posted by Gordon McLeod (Member # 33) on 11-28-2000, 05:30 PM:

At one time Photographic analysis (they also distributed spliceing tape) had a light meter calibration service
THe since trim pot is not the only one that needs ajusting THere is also a min and max and curve pot on the amplifier board inside the handle

Posted by Alan Gouger (Member # 543) on 11-29-2000, 09:43 PM:

Has anyone had any experience with the PSA 200.
Im thinking of buying one!

Posted by John Pytlak (Member # 331) on 11-30-2000, 05:46 AM:

Kodak owns several PSA 200 Projection System Analyzers. They are very useful for setting final lamphouse alignment and focus, as they provide a display of screen uniformity measured in the auditorium, but conveniently displayed on a laptop screen that can be positioned in the booth. There is some cabling, boot-up, and set-up time required, so a handheld meter is more convenient for a "quick check" of luminance and uniformity. If you are a service tech who does lots of complete lamphouse alignments, the PSA is very handy. For day-to-day checks in a theatre, a handheld meter will probably find more use.

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

Posted by John Walsh (Member # 168) on 11-13-2003, 04:55 PM:

Bringing up an old topic....

We are looking for a second light meter. The Sekonic L-508 Cine Zoom Master was suggested. I seem to remember reading somewhere that, since it 'sampled' the light at a slower rate than the 48 flashes per second MP projectors operate at, it was not suitable for theater use. But as I check the info at the web site, it says it does have adjustable FPS setting.
here

Pentex Digital Spotmeter was also suggested, but again I don't know if it's suitable.
here

For a 'second' meter, I would be happy with one that was only accurate to +- 1fL. We have a LS100 for critical measurements, or to check cheaper meters.

Any suggestions....?

[ 11-14-2003, 10:57 PM: Message edited by: John Walsh ]

Posted by Mark Gulbrandsen (Member # 72) on 11-13-2003, 07:08 PM:

At CLACO we have USL PSA lightmeter serial number 1. Its been around for quite a while now and we use it constantly. Great for when you're doing lamphouse/reflector upgrades and we even use it for setting up 15kw lamphouses at a 15/70 3D theatre! VERY versatle and without a doubt ULS's best and most useful product. The meter is in Wyoming right now and was just used on a new 8 plex install.
Mark @ CLACO

Posted by John Pytlak (Member # 331) on 11-13-2003, 07:35 PM:

That fps calibration on the Sekonic is for when it is being used as a meter for motion picture cameras --- it factors in the exposure time to calculate the lens stop.

As mentioned in my article, any spot meter that measures reflected light accurately can be used if it is calibrated against an "official" screen luminance meter like the Minolta LS-100. But many meters intended for photography can at best read light within 1/3 of a stop --- in other words, they can barely show the difference between 12, 16, and 20 footlamberts, much less have an accuracy of +/- 1 footlambert. And the calibration of a "non-standard" meter would only apply to the particular conditions you calibrated it to, e.g., a two-blade shutter (48 interruptions per second) and approximately 5400K color temperature.

Posted by Paul H. Rayton (Member # 1817) on 11-13-2003, 07:48 PM:

I have a "Spectra", which I use at my theatre, but the way I got it saved some money.... At the suggestion of a dealer, I purchased a Pentax meter, and then took it out to Spectra and paid them the "conversion" fee to have it set up for reading specifically foot-Lamberts. This saved me a few hundred $$, but may not be practical for those not residing in the Los Angeles area.
At that time (about 8 years ago), Spectra did not impress me so negatively.
I have recently seen more people carrying around the Minolta meter. But you probably can't take a similar dollar-saving shortcut, since it is built and set for reading screen luminance by the same company. No "financial shortcut".
The only problem with sharing a somewhat fragile device among several locations and different people is the "rental car" syndrome: "It's not mine, so I don't really have to take particular care of it." Even studio-owned light meters here locally are sometimes showing signs of wear and tear, and some techs will trust my own personal meter rather than the multi-user studio meters.
But some meter is better than no meter!

Posted by Manny Knowles (Member # 1171) on 11-13-2003, 08:34 PM:

Can anyone provide list prices or even "ballpark" cost for some of these products?

In particular, I'm interested in the USL PSA-200. I checked the Ultra-Stereo website and they don't list a price.

Posted by Gordon McLeod (Member # 33) on 11-13-2003, 09:16 PM:

This is from Verns website
http://www.cin-tronics.com/News_letter.htm
and there is an article on the problems with that meter
The FPS is for camera exposure settings

Posted by Steve Guttag (Member # 268) on 11-13-2003, 11:12 PM:

We have three now...the Spectra Cine-Spot that reads in fL and f-cd. It is great for measuring screen gain. It also reads down to .01fL for contrast measurments. Its biggest drawback is that it is an unlit LCD screen...kinda rough in a dark environment.

We now have the USL PSA light meter system. This is an excellent tool. It allows for precise alignment and also for near perfect balance between the projectors in a mulitple projector installation. Ours will do both 2-wing and 3-wing shutters. It also will measure Jitter, Weave and lamp stability. Another advantage of it for us is that you can save a report so you can provide documentation to the customer.

It only reads down to .1 fL so it isn't useful for contrast measurments but it does most everything else. It also tops out at 40 or so fL without using Netrual-Density filters...not a real problem since we target for 16fL

The latest edition to our light meter arsenal is the USL Color Meter. This will read out down to .001fL. As the name implies it also measures the color of the light in X and Y coordinates and also lists the equivalent "temperture" in Kelvin.

All of the above have their place and all are excellent in their own way...if I could have only one...it would probably be the PSA.

Steve

Posted by Michael Schaffer (Member # 1204) on 11-14-2003, 01:17 AM:

What about this Minolta light meter?

And here is a question about the USL system: why is the version for 3-blade shutters more expensive than for 2-blade shutters? Isn`t it just a software feature to switch between the two types of shutters? Does it work with XP?

Posted by John Walsh (Member # 168) on 11-14-2003, 08:05 AM:

I have a quote on my desk for the Minolta LS-100/LS-110. Either model is $3145.00. They do leasing, and an extended warranty is $450.00.

Posted by Steve Guttag (Member # 268) on 11-14-2003, 09:05 AM:

The 3-wing and jump/weave stuff is indeed an additional expense and it is also just a software difference. However, how do you charge for the extra time and expense to develop those software versions (and keep them supported on future software upgrades) without having to charge everyone for them? How many people deal with 3-wing shutters?.

Dolby wanted to charge to activate the Dolby-E decoder within a CP-650...think about it...the processing and software already reside within the processor...they just wanted to charge you to activate it. This idea of charging for software isn't a new thing...check out Microsoft! As to the CP-650...this is a past-tense thing...Very few CP-650 installations ever would want the Dolby-E decoding since it is strictly a pre-broadcast medium. The ability to perform that function goes away with version 2.2 or 2.3. The processing space is going to be used elsewhere. I do some rather off-the-beaten-path installations and I only have two CP-650s that are Dolby-E capable...they are at a university with a film program that supports both film and video.

Manny...as to your request...here are the LIST prices for the PSA:

Standard 48Hz model: $3,995.00
48/72Hz model: $4,395.00

Jitter Weave Upgrade to either: $425.00

Steve

[ 11-14-2003, 04:21 PM: Message edited by: Steve Guttag ]

Posted by Erick Akers (Member # 875) on 11-14-2003, 03:24 PM:

I just picked up a Spectra for $230.00 U.S.,
and it works great!!!

Unless you absolutly need one now, it pays to shop around.

I doubt anyone would dissagree that I got a hell of a deal!!!

Posted by John Hawkinson (Member # 1135) on 11-14-2003, 03:53 PM:

The LS-110 and the LS-100 are the same price? What's the difference? We've been using an LS-110 since there's one conveniently available...I just assumed the 110 was as good as the 100 for cinema use. Is that a bad assumption?

--jhawk

Posted by John Walsh (Member # 168) on 11-14-2003, 11:03 PM:

The info on the LS-100 is here

And the LS-110 is here

Posted by John Hawkinson (Member # 1135) on 11-15-2003, 12:36 AM:

Thanks, John; I was looking for a comparison with respect to suitability for cinema usage, though. I guess the difference is the LS-110 has a 1/3-degree angle. I would hope that's not a problem, but was hoping someone (John P.?) could comment.

--jhawk