Film-Tech Forum ARCHIVE: Luminosity envy (mine is brighter than yours)

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Posted by Peter Berrett (Member # 672) on 05-29-2001, 08:32 AM:

Hi all

A friend from the Coburg Drive-in has been kind enough to answer a few of my questions about fls, luminosity and the relative brightness of cinema vs drive-ins screens. I was surprised to find out that most drive-ins only have about 6fls of brightness vs 16, 21 fls etc in cinemas.

I am sure that there are a few drive-in operators out there who follow these forums. What level of brightness have you been able to get on your screens? It has been explained to me that the larger the surface area of the screen the less luminosity there will be so lighting up a large screen must be something of a technical challenge.

Who has the most luminous drive-in and how was the level of brightness achieved? Is it easy/possible to get 16fls on a large drive-in screen?

cheers Peter

Posted by John Pytlak (Member # 331) on 05-29-2001, 09:36 AM:

Most drive-in screens are painted with matte white paint, which at best is equivalent to a matte white screen having a gain of about 1. Weathering quickly reduces the "whiteness", so after a few months the gain is much less.

A "rule of thumb" for lighting a matte white gain=1 screen is that you need about 5 watts per square foot of anamorphic screen area to achieve 16 footlamberts with a normal 2-blade shutter (50% light efficiency). So a 20 x 48 foot scope image having 960 square feet would need about 5000 watts, and a 25 x 60 foot image having 1500 square feet would need at least 7500 watts to properly light a matte white screen.

But as the lamp power is increased, the effects of heat on the film become significant. The power from a 6000 or 7000 watt lamphouse going through a 35mm frame of film will cause permanent damage to the film if carelessly "hot spotted", or if the infrared heat energy is not efficiently removed by proper filtration. Thermally induced "focus flutter" is also an issue at high power levels. For 35mm film, 7000 watts is about the largest lamp that is practical, even when proper heat control measures are in place.

Drive-ins "push the envelope" in several ways. High speed "drive-in" intermittents having faster pulldown can allow a smaller shutter blade having greater efficiency. "Drive-in" shutters may use slightly smaller blades that don't completely cover the film pulldown, trading a bit of travel ghost for a few percent more light. Water cooled gates are widely used. More efficient lenses offer some help. Some have experimented with silver paints or more directional screen surfaces. But more than likely, any drive-in with a screen larger than 25 x 60 feet will find it difficult to achieve 16 footlamberts. A 50 x 120 foot screen has four times the area, and at best, only 1/4 the screen luminance of a 25 x 60 foot screen.

For really huge screens, 70mm prints would allow more power to be used, since the energy is spread over a much larger area on the film. This fact has sadly been forgotten by many.

------------------
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 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Peter Berrett (Member # 672) on 05-30-2001, 04:39 AM:

Thanks John

Coburg Drive-in here in Melbourne has a screen about 33 metres (110ft) in width. Taking a guess at its height (48 ft?) that works out at about 5,280 square feet which, using your calculation works out at about 26000+ watts to get 16fl on the big screen.

Fortunately I'm told that Coburg has projectors with water cooled gates and can run 70mm film which would spread out the light over a larger area but I take it that even over the larger area of film this level of wattage would melt the film. Getting the 16fls could be difficult.

cheers Peter

Posted by Dave Bird (Member # 490) on 06-01-2001, 06:53 PM:

I brought this thread back partly because it's touched on again in the Moulin Rouge thread above.

I don't think I've ever heard what the average INDOOR luminance is. Some conversations I've had locally with some theatre folk seem to indicate that a 3-4K bulb is still very large, "only drive-ins use those". So I'm wondering, with the new large "wall-to-wall" huge screens, are INDOOR theatres now "cheating" like the DI's always have "underlamping"? Or are they up into the 5-7K bulbs (5W per sq.ft.) as John prescribes?

Posted by Gordon McLeod (Member # 33) on 06-01-2001, 08:03 PM:

Most of the larger screens are running 5-7K lamps in an attempt to reach the goal of 16fl on some of the larger sheets

Posted by John Pytlak (Member # 331) on 06-01-2001, 08:51 PM:

The news is not good. A Lucasfilm TAP survey found that the average screen luminance for FIRST RUN theatres was only about 11 footlamberts. About 90% of the theatres that request certification by the Kodak ScreenCheck Experience program need remedial work to meet the aim of 16 footlamberts. ScreenCheck has found some screens as low as 5 footlamberts in the center, and 2 at the corners! A dim screen is NOT "Film Done Right".

Posted by Gordon McLeod (Member # 33) on 06-01-2001, 09:19 PM:

I rather doubt it will change since the trend is to larger screens than 35mm will withstand the energy of
Maybe it is time to rethink the 16fl issue to be more practacle in the reality of the realworld
WHich would look worse a print timed for 12fl projected at 12fl or a print timed for 16fl and projected at 12fl

Posted by David Kilderry (Member # 142) on 06-01-2001, 09:25 PM:

Supervising a circuit of several hundred screens both indoor and outdoor, I can tell you that we have done a lot of work in recent years to improve the level of light on our screens.

The single biggest step in the right direction for us was the purchase of a light meter for theatre use (we bought the Spectra Cine, but other fine meters are available). Both Kodak and the local filmlab use the same meters here and they are calibrated alike. This ensures we are all singing from the same hymn book.

We found several screens below 8 fl and a few over 30fl! We set about upgrading lamphouses, mirrors (reflectors), lenses, rectifiers (power supplies), and embarked on an annual screen cleaning program with factory trained cleaners using the correct chemicals and method. My post under the Moulin Rouge topic explains the areas we look at specifically.

Our largest indoor screens now use 7,000 watt lamps and we use everything else all the way down to 1,600 watts on our smallest screens. Outside of our drive-in screens, none of our light should be below 14 fl at screen centre. Most are close to 16 fl with many exceeding this on c/s.

Looking at one of the show prints of Moulin that we are running again yesterday, this film just dazzles and cries out for light at or slightly above 16fl. It looks very flat if screened otherwise.

Now, back to our quest to increase the light on our 110 ft drive-in screen.

David Kilderry

Posted by Peter Berrett (Member # 672) on 06-01-2001, 10:14 PM:

This is really a consumer affairs issue. It is arguable that a movie theatre patron is entitled to a minimum level of luminosity and that cost-cutting by way of the use of dimmer lamps is the cinematic equivalent of filling half a popcorn bag with air.

I wonder whether a set standard of luminosity should be agreed to under a voluntary code of conduct that could be set up by the industry. Given technological restraints there could be different standards for drive-ins and for cinemas. I would suggest that 6fls for drive-in theatres and 14 fls for cinemas would be a reasonable standard given. Alternatively there could be a common standard expressed in terms of watts/square foot.

It would be an interesting exercise to see which cinemas/theatres here in Melbourne would not currently meet these standards.

Turn up the brightness.

cheers Peter

Posted by John Pytlak (Member # 331) on 06-02-2001, 06:58 AM:

Screen luminance and viewing conditions for screening rooms and indoor theatres is specified by standard SMPTE 196M. The aim is 16 footlamberts, with an allowed range for theatres of 12 to 22 footlamberts.

SMPTE Recommended Practice RP12 specifies screen luminance for drive-ins. It recommends an aim of 16 footlamberts, but allows a lower limit that should never be less than 4.5 footlamberts.
http://www.smpte.org/standards/

Posted by John Pytlak (Member # 331) on 06-02-2001, 07:13 AM:

Gordon said: "Maybe it is time to rethink the 16fl issue to be more practacle in the reality of the realworld
WHich would look worse a print timed for 12fl projected at 12fl or a print timed for 16fl and projected at 12fl"

Timing a print for 12 footlamberts (i.e., making the print lighter) will compromise quality. A lighter print will lose detail in the highlights, have pasty looking flesh tones, desaturated colors, and smoky/milky shadows. It won't really look better at 12 footlamberts than a properly timed print, and will definitely look worse at 16 footlamberts.

David Kilderry is correct that image quality improves dramatically as screen luminance is increased -- there is no real reason that today's 35mm projection technology cannot properly light screens up to about 25 x 60 feet. And if theatres insist on having screens that are 30 or 35 or 40 feet high, there is technology that has been around for 45 years that can do the job -- 70mm prints.

IMHO, sinking to the lowest common denominator is NOT the solution to dim screens.

Posted by Brad Miller (Member # 2) on 06-02-2001, 03:41 PM:

I replaced a very old 4k lamphouse (with a reflector that was in horrid condition) at a theater yesterday with a Christie SLC 4k lamphouse and everyone who saw the test run was just staring in awe at how incredible the image looked. I didn't have my light meter, but walking next door to the other identical auditorium still running a 4k lamphouse (with decent reflector) was like night and day. Suddenly that old lamphouse, which everyone had been pleased with up until last night (except for the projectionists and myself), just looked like PURE CRAP compared to the current model Christie next door.

Sometimes people need to look at their equipment and realize that technology does improve over time. I'll bet that even with a brand new reflector in the old 4k unit, I could stack it up to a Christie SLC running a 3k lamp and the Christie would still be a no contest winner.

As far as timing prints at 12fl, please NO! We ran Pearl Harbor through in that auditorium and even with a regular release print (2383 stock), it looked absolutely outstanding!

Posted by John Pytlak (Member # 331) on 06-04-2001, 07:29 AM:

"Brighter is Better".

The reason a print looks better at the proper screen luminance has to do with human vision. Apparent sharpness increases with higher light levels --- that's why it's easier to read fine print with a good reading light than in dim light. Colors also improve as light levels increase --- for example, colors seem more vivid on a bright sunny day than on a dark and cloudy day, and under dim moonlight even bright colors appear almost black-and-white. Quality improves dramatically going from 8 footlamberts to the aim of 16 footlamberts, and SMPTE 196M allows up to 22 footlamberts.

As Brad notes, "everyone who saw the test run was just staring in awe at how incredible the image looked." with a brighter image.

Posted by Peter Berrett (Member # 672) on 06-05-2001, 04:47 AM:

Thanks John

I have yet to see a 70mm print at our local drive-in. I understand that they can be hard to get. It would interesting to compare the brightness on the screen.

By the way this begs a question that has puzzled me for a while. Why is there no such thing as 140mm film, 280 mm film etc? Logically as the size increases the light you can shine through each frame should increase as well so for driveins the large film size would be very handy.

I found a history of film sizes at
http://www.xs4all.nl/~wichm/filmsize.html

but the only reaons give that there are not larger sizes is that teh film isnot strong enough. I would have thought that with all the wonderful new materials being developed like kevlar a new larger format would be possible.

Have your technical staff at Kodak developed a larger print standard?

cheers Peter

Posted by John Pytlak (Member # 331) on 06-05-2001, 07:21 AM:

For motion picture use, 65mm / 70mm is probably the largest size practicable. For the very large IMAX format (15-perf 70mm), reliably tranporting and registering such a large frame required the development of unique projection technology ("rolling loop").

Yes, a larger format could be developed, but the image quality of modern films offers excellent quality on huge screens, especially with 70mm prints.

Posted by David Kilderry (Member # 142) on 06-08-2001, 09:03 AM:

Today we are seeing 5,000 watts through 35mm without water cooled heads (Kinoton FP50 and Cinemeccanica Vic 5) and no adverse effects. Add water and we run 7,000 watts and still have the film staying in shape and don't burn our fingers on the gate!

If 70mm film was run exclusivly through a conventional maltese cross movement projector (not a Jones rolling loop) what size lamp would the film handle?

The light (heat energy) is spread over a much larger frame. Would it handle the new 10,000 watt xenons? Is a 70mm release of major films viable if they continue to have screens 60ft plus in width? I love big screens, but if they only have 10fl or less it defeats the purpose.

David Kilderry

Posted by John Pytlak (Member # 331) on 06-08-2001, 12:32 PM:

David Kilderry asked: "The light (heat energy) is spread over a much larger frame. Would it handle the new 10,000 watt xenons? Is a 70mm release of major films viable if they continue to have screens 60ft plus in width?"

The projectable image area of a 5-perf 70mm print is 1.912 x 0.870 inches (48.56 x 22.10 millimetres). The projected image area of 35mm "scope" is 0.825 x 0.690 inches (20.96 x 17.53 millimetres). So the image area of 70mm is almost three times greater than that of 35mm scope. Theoretically, with proper heat filtration and gate cooling, you could put three times the radiant energy through that 70mm frame, compared to 35mm.

In practice, the largest lamphouse available for that format today is 10,000 watts (e.g., the Kinoton Universal Lamphouse or other lamphouse designed for special venue 70mm). If the energy is spread uniformly across the 70mm frame, 10,000 watts is certainly practicable.

Making 70mm prints for huge screens is certainly viable. 65mm/70mm films are readily available from Kodak. Several labs worldwide (e.g., CFI, Technicolor, Imagica, etc.) have printing and processing capability, including "blow up" printing from 35mm originals. DTS Digital Sound has proven itself reliable with the 70mm releases of "Titanic" and "Vertigo". Distributors have been willing to make special 70mm prints for some European theatres (e.g., Spektrum, Kinopolis) and premier events.

But 70mm prints do cost considerably more than 35mm, primarily due to the cost of making the 65mm printing negative, and the more labor-intensive and slower printing and processing operations required (e.g., printing the DTS timecode now requires a second pass through the printer). Hopefully, the "Splendor of 70mm" will live again.

Posted by Peter Berrett (Member # 672) on 06-09-2001, 01:55 AM:

This begs a question then.

Do the benefits of screening in 70mm at a Drive-in outweigh the costs?

Put another way what is the practical experience of drive-in theatre operators? If you make a much brighter and better picture does this translate to more $$$ through the gate and is this sufficient to defray the extra costs associated with running 70mm?

Sadly, I have a suspicion that many drive-in patrons do not worry overly about the degree of luminosity as long as the picture quality is adequate. The drive-in 'experience' is more than just what is on the screen.

Still I look forward to seeing a brighter image at my local drive in one day.

cheers Peter

Posted by Dave Bird (Member # 490) on 06-09-2001, 10:02 AM:

The best way is to attend "country" drive-in's where the screens are 50-60 ft. There is one reasonably nearby here that was 14.5fl
when intstalled, it's stunning and LOOKS bigger than screens I know to be larger. Not surprising when we hear that even indoor screens average less light.

Next question, not sure we ever covered, where a 35/70 projector was set up for 16fl
(let's say with a 7K bulb), how much light would be achieved with 70mm on the same screen with same bulb? (I'm assuming they wouldn't change lamps). Is there a gain or loss?

Posted by Aaron Sisemore (Member # 145) on 06-09-2001, 06:00 PM:

>>Put another way what is the practical experience of drive-in theatre operators? If you make a much brighter and better picture does this translate to more $$$ through the gate and is this sufficient to defray the extra costs associated with running 70mm?<<

If you can convince the studios to strike 70mm prints for drive-ins (since that they wouldn't do the same for a hardtop anyways),then I will be truly amazed!! The studios couldn;t give a rat's ass about a drive-in..

>>Next question, not sure we ever covered, where a 35/70 projector was set up for 16fl (let's say with a 7K bulb), how much light would be achieved with 70mm on the same screen with same bulb? (I'm assuming they wouldn't change lamps). Is there a gain or loss?<<

Depending on the lenses and screen sizes, there would be a HUGE gain in luminance with 70mm for a given wattage comapred to 35. You simply can force more light thru a bigger hole

-Aaron

Posted by Peter Berrett (Member # 672) on 06-09-2001, 10:23 PM:

Funny...

I drove by the Coburg drive-in today and looked up to see somebody chainsawing the ends and top from Screen 1 (110 foot wide). ZZZZZZZZZZZZZzzzzzzz

Well - its one way to get a brighter picture <smile>

cheers Peter

Posted by John Pytlak (Member # 331) on 06-10-2001, 06:46 AM:

Peter said: "I drove by the Coburg drive-in today and looked up to see somebody chainsawing the ends and top from Screen 1 (110 foot wide)."

I'd hate to think they are doing it because someone read Film-Tech and found they could't get 16 footlamberts on a 110 foot screen. With 70mm prints, they might be able to.

Frankly, if light were the issue, I'd keep the huge screen and use a longer focal length lens when I didn't need to fill the full screen for a full lot. Just encourage people to park closer to the smaller, brighter image.

Posted by David Kilderry (Member # 142) on 06-12-2001, 04:20 AM:

OK Peter and John, I get the point. Just give us a chance to boost the light with the existing focal length and screen size. I do not want to be responsible for cutting down the size of Australia's largest operating drive-in screen!

We have a lamphouse and rectifier (power supply) upgrade on its way with 7,000 watts. Screen repaint is due this year and new lenses if necessary. We will give Theatre One at Coburg every opportunity to produce some decent light. All screens are 70mm capable if anyone ever makes a print available again for a drive-in.

Oh, and more scope prints please shot a few stops over!

Check it out at......

David

Posted by Peter Berrett (Member # 672) on 06-12-2001, 09:14 AM:

David said

"OK Peter and John, I get the point. Just give us a chance to boost the light with the existing focal length and screen size. I do not want to be responsible for cutting down the size of Australia's largest operating drive-in screen!"

Just kidding David. We love your Drive-in but more light is always welcome.

"We have a lamphouse and rectifier (power supply) upgrade on its way with 7,000 watts. Screen repaint is due this year and new lenses if necessary. We will give Theatre One at Coburg every opportunity to produce some decent light. All screens are 70mm capable if anyone ever makes a print available again for a drive-in."

Actually for readers, Theatre 1 isn't all that bad now. I've been there and it looks ok. You can never have enough footlamps however.

For those wondering what all this discussion is about you can have a look at the Coburg Drive-in at the following link.
http://www.drive-insdownunder.com.au/australian/vic_coburg.htm

The establishment is well run, always clean.
and the staff are friendly (no I don't own shares in Village).

The Drive-in is easily accessible from the city centre (about 15 minutes drive) so if you are visiting Melbourne for any reason it is a must see.

cheers Peter

Posted by Dave Bird (Member # 490) on 06-13-2001, 03:36 PM:

If you click on the link above, not only will you see a beautiful drive-in, but listen to this..... Realizing that a market exists, two RIVAL chains actually run this together. Not only that, they're adding to the "feel" with old billboards and nostalgia everywhere with a fabulous snack bar! I also noticed in another topic, David mentioned that they have new intermission films struck every 3 years AND RUN PROMO SNIPES AT THEIR INDOOR MULTIPLEXES!!! How refreshing is that? Two chains realizing that there is a market here, and doing a "bang-up" job at that! Take a look at the pix, and then you tell me if ANY chain (let alone two) in the world is putting this much effort into an outdoor, well done!

Posted by Peter Berrett (Member # 672) on 06-14-2001, 06:48 AM:

The good thing at this stage is that it is popular without becoming so popular that a lot of people you'd rather weren't there show up. The crowd that show up are pretty well behaved. In fact a lot of the patrons are quite yuppiesh - you see lots of 4 wheel drives!

It is good however to see that the drive-ins are successful and that in recent years they have been adding screens. My great hope is that someone will reopen the Wantirna Drive-in Theatre which is near to where I live. Coburg services the northern suburbs of Melbourne and Dromana largely services the southern suburbs of Melbourne however for residents of the eastern suburbs it is an hour's drive to either drive-in theatre.

The Wantirna Drive-in is thankfully largely intact and would enjoy bumper crowds from day 1. It is a real shame to see a largely intact drive-in in an populous area of young families sitting idle. Arguably it should never have been closed. It was owned by Trash and Treasure who run a sunday market there every week for a while and then was purchased by the State Government as a potential site for a public hospital. Thankfully this proposal fell through and the site now sits in limbo.

Recently I nominated the site to the National Trust as a site of significant historical interest. The snack bar has a unique architecture. It looks like a Pizza Hut with a projection room in the roof!

The site is largely complete and includes a ticket box, snack bar including inbuilt projection room and a separate brick projection room built later. The ramps are intact. All it really needs is three x 160ft screens (yes - 160ft screens - wouldn't that give a huge image!), 70/35mm projectors, some radio transmitters and some TLC.

Where are our cinema entrepreneurs? As the site is sitting idle chances are that the site could be leased for a peppercorn rent. The foundations for the screen are there - just buy a second hand drive-in screen from a country area set it up and make a fortune from all the young families in the area. Arguably the drive-in would be more profitable than some cinemas in Melbourne at present!

Perhpas a new (to Melbourne), aggressive, entrepreneurial cinema chain with loads of cash (ARE YOU LISTENING READINGS?!) might give some consideration to re-opening this Drive-in.

Won't somebody please re-open the Wantirna Drive-in Theatre?

<smile>

http://members.optushome.com.au/pberrett/drivein/theatre.html

Let's have some more luminosity at Wantirna.

cheers Peter

ps sorry to ramble on again about Wantirna but seeing this cinema open again is my holy grail.

Posted by David Kilderry (Member # 142) on 06-16-2001, 02:04 AM:

Dave,

Thanks for your great comments about Coburg drive-in. Hoyts sold out of the venue in the early 1990's and it has been 100% Village Theatres since that time.

It was built as an independent in 1965, was acquired by Hoyts in 1968 and closed by them in 1984. Village and Hoyts re-opened it in 1987. It is the last drive-in operated by Village who once had 40. It was also the last drive-in that Hoyts had any interest in.

It will feature on the nightly news next week here (Channel 7) and has had radio and news articles on it in the last week, all this when we are in mid-Winter! No, it does not snow here so drive-ins run all year round.

Peter:

You are on the right track with Wantirna, it was a beautiful site. It is very difficult however for anybody to commit to the location once it was bought by the Govt who could decide to build that hospital at any time.

David Kilderry

Posted by Dave Bird (Member # 490) on 07-04-2001, 12:10 PM:

Hey, if David really was chainsawing the screen to get more light

,
don't laugh, it's been done before. Look what I stumbled on today,
the recently closed (last year) Edgemere in Shrewsbury Mass did just that. You've gotta see it, there really is nothing new under the sun!
www.drive-ins.com/detail.php?code=maedge

Posted by Peter Berrett (Member # 672) on 07-05-2001, 04:10 AM:

Dave

Fortunately there are less destructive ways of increasing luminosity!

David

Yes it would take a bit of cash to get Wantirna up and running but not as much as you might think. One would not have to buy the site - one could simply lease it from the Government until such time as they decide what they are going to do with it. At present it is still used on Sundays by Trash & Treasure and idle the rest of the week. The Government would probably be glad for a little extra revenue generated from the site.

I have been told that in the past there was a consortium that wanted to reopen Wantirna but Trash & Treasure wouldn't play ball. With T&T sidelined there is no impediment to a new operator making a bid to reopen the site.

The main expense as I see it is the screen. The foundations are there - maybe a country drive-in screen could be bought cheaply second hand and reconstructed on the site (Yarrawonga?). A major cinema chain probably would have a spare projector lying around somewhere. Snack bar and projection rooms exist already. The only other thing would be some repainting of the ramps and a FM transmitter for sound.

Even if Wantirna is never open full-time again I hope that somehow there could be at least one more night when movies are shown at Wantirna, perhaps with a portable screen. It would be a memorable night (particularly if the former resident prostitute turnes up!).

cheers Peter