This is topic What is the largest screen possible with today's lamphous and 35 mm technology? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


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Posted by Kevin Wale (Member # 1851) on 10-02-2003, 07:27 PM:
 
Title says it all. I'm just wondering if anything approaching IMAX size is even possible with a 35mm projector.

I assume the lamp technology is there. The hinderence I think of is the lenses.

Any ideas?
 

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Posted by Gordon McLeod (Member # 33) on 10-02-2003, 08:57 PM:
 
The limitation is the film itself 35mm wide the size of a postage stamp
It has a fixed amount of resolution
and can handle a finite amount of heat aka light
35mm really shouldn't be asked to make a scope picture bigger than 48-52'
 

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Posted by Aaron Sisemore (Member # 145) on 10-02-2003, 10:28 PM:
 
You are limited only by the lamp wattage and the throw distance. Remember the larger the screen, the more might energy required to illuminate it to the proper brightness levels. The largest xenon lamp that can be safely run with 35mm film is 7000W. Scope will be a bit brighter than flat for a given set of parameters. The shorter the throw, the more wattage you will need to light up a very large screen. Keep the throw long, and you can use longer lenses. Huge screens with short throws are very difficult to do right with 35mm. To completely fill an IMAX screen would be near impossible to do because of vignetting issues and lamp wattage.

-Aaron
 

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Posted by Steve Kraus (Member # 476) on 10-03-2003, 11:08 AM:
 
There is probably some way to do it with a Cinefocus gate hooked up to a source of refrigerated air.
 

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Posted by Kevin Wale (Member # 1851) on 10-03-2003, 11:48 AM:
 
I was driving and I saw our old abandoned drive in screen and I thought... why can't we put a screen that size in the auditorium? I feel as do most it seems, that larger screens are the future of cinema. If you sit on the back row of many theatres, it's litterally not much different than watching my parent's 55" Mitsubishi 16x9 hidef tv.

I hear everyday people talking about how such and such movie will be great but that they are waiting for the DVD. It seems that more and more every day only the big big big movies(LOTR, Matrix, SW, etc.) are really catching people's interest in the long run. Before we did our lamphouse upgrades, EPII looked 100 times better on our hidef than it did at our theatre. This is likely the case at many theatres.

IMAX is in the drivers seat with all the digital mastering going on. Since they can get those movies early now I can see that they may litterally replace what we think of as the cinema. However, it totally cuts off the edges of the picture. Even flat is wider than IMAX. Nothing beats the original Star Wars in scope. To me even IMAX wouldn't.

So, I just kinda got off in my what if mode wondering what if there was IMAX size for those who need something more than what is currently offered, while retaining widescreen for those of us who have that odd emotional attatchment to 2.35:1.

I guess now is a good time to be thinking about it... someone will be the guy who infuses old time life back into the industry. I just hope we don't have to compromise some of the things that TV has compromised for so long.
 

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Posted by Daryl C. W. O'Shea (Member # 1303) on 10-03-2003, 11:51 AM:
 
Yeah, maybe somebody should develop a 70mm system for regular theatres.

You don't need digital technology to make 'big' movies. You just need some extra money for the extra film and the equipment to show it.
 

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Posted by Aaron Sisemore (Member # 145) on 10-03-2003, 11:59 AM:
 

quote:

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I was driving and I saw our old abandoned drive in screen and I thought... why can't we put a screen that size
in the auditorium?

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quote:

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Why do longer lenses need less wattage? I thought wattage was determined by screen size only, not throw.

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Shorter lenses refract light at wider angles to magnify an image for a large screen/short throw situation (as many new stadium-seated theatres are using), thus require more light (and therefore more wattage) to produce a given level of brightness than the same size screen with a longer throw distance.

Example: A 46x19 screen with a 52' throw (and a short focal length lens) will require more lamp wattage to get 16fl than a 46x19 screen with a 150'throw (and longer lens).

-Aaron
 

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Posted by Alan Haigh (Member # 1781) on 10-05-2003, 02:47 AM:
 
Thanks Aaron

So long focal length lenses are more efficient than short ones. Presumably the short ones get hotter? Is it a big difference in efficiency?

Alan
 

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Posted by Paul Mayer (Member # 355) on 10-05-2003, 12:49 PM:
 
Up to a point. After a certain focal length, long lenses simply can't have their elements be wide enough to keep the f ratio down (that's where 4"-wide lenses come into play). Shorter lenses generally require more glass elements in their design to correct optical abberations that become very noticable at wide projection angles. Those extra elements and the resulting extra air-glass and glass-glass transitions eat up light even when the best optical coatings are used. In the end, the fastest lenses exist in the middle range of focal lengths, with both short and long lenses being slower in terms of f ratios (higher f numbers mean slower lenses and therefore less light).

Although a faster lens will put more light on the screen (all other things being equal) faster does not automatically mean better. Depth of focus becomes an issue with fast lenses. From what I've seen and read if one stays within a range of about f2.0 to f2.8 one can expect good depth of focus and reasonable light output. Faster than that with short lenses and/or high keystone angles may result in an inability to get the whole image to focus simultaneously.
 

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Posted by Alan Haigh (Member # 1781) on 10-05-2003, 04:43 PM:
 
So to some up my disparate thoughts on this thread:-

For a big screen you need
A big lamp (7kW)
A lamphouse with good optics, well aligned.
A good lens with a medium focal length, also no keystoning etc.
A "high gain" screen
port hole glass that isn't fireproof (?!)
Cooling!
Large amount of money to replace lamps every few hundred hours.

And then you're OK up to 50 feet, or 60 with a following wind. Any more and the film starts to buckle with the heat.

Not for the faint hearted then!
 

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Posted by Bevan Wright (Member # 1884) on 10-05-2003, 05:17 PM:
 
>60ft is definitely possible given the following:

1) 6kW lamp - you can easily reach 35mm's thermal threshold with a 6kW lamp if it is properly set-up, maintained and aligned, 6kW also seems to be a more efficient lamp and lasts longer than a 7kW in most cases - unless you are going to very short arcs.

2) Modern reflector optics (horizontal)

3) ISCO RED lenses or Schneider Cinelux - hopefully someone buy's ISCO out of bankruptcy before they go away.

4) AR coated, both sides (single pane) port glass - double panes in most cases just mean a few more surfaces that don't get cleaned.

5) Proper alignment - light meter must be present when changing lamps and checked every few weeks due to arc burn-back.

6) Good prints - show prints preferably, although I have seen some good high-speed prints but they are few and far between.

7) Perlux II screen - It kills me when people want to do >50ft matte white screens.

8) Cooling - I've seen 6kW lamps go for >1,800 hours before needing to be changed because the booth was kept VERY cool. Watercooling only helps the 'finger burn' factor but may be necessary depending on the projector.
 

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Posted by Richard Fowler (Member # 893) on 10-05-2003, 08:59 PM:
 
Water cooling is more neccessary on machines with brass castings such as a Century. Kinoton with - kind to film - Delrin runners also require cooling at high temperatures. Machines with machined aluminum support with matte box stepped light baffle as used in the Kelmar conversion kits and on machines such as the Christie, can dissipate the heat more easily so water cooling option is not usually offered. Glass cold coated reflectors also do a better job of light output versus heat than coated metal units.
 

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Posted by Gordon McLeod (Member # 33) on 10-06-2003, 09:35 AM:
 
I have found that the Kelmar aluminum ones are terrible for focus drift with large lamps when they get hot
 

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Posted by Paul Trimboli (Member # 1509) on 10-07-2003, 08:02 AM:
 
Just wanted to add that at the IMAX SR cinema I work at we have a Cinemecannica with a Strong X60D lamp house running a 7k lamp on a 22meter screen! Water cooled gate of course! Schnider optics. I know most IMAX SR theatres have the port for 35mm and there are even pictures on film-tech showing them! The light does go out at the corners, but I think it looks good and people love watching movies on a huge screen!
 

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Posted by John Pytlak (Member # 331) on 10-07-2003, 08:20 AM:
 
With good engineering design and care in equipment selection and alignment, you certainly can go larger than 25 x 60 feet. But please don't sacrifice image quality for size --- standard SMPTE 196M specifies no less than 12 footlamberts at the center of the screen, with the screen sides between 75% and 90% of the center reading, and no less than 10 footlamberts anywhere on the screen.
 

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Posted by Steve Kraus (Member # 476) on 10-07-2003, 07:46 PM:
 
Design suggestion for Bevan...but I think I should put it in the other thread.
 

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Posted by Kevin Wale (Member # 1851) on 10-08-2003, 01:20 AM:
 
This has been a very educational thread. Thanks for participating in this thread so much. I have to read and reread to soak it all in. Then I have to really try and grasp all the ideas. It's so great being amongst so many knowledgable people.
 

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Posted by Jim Leko (Member # 1287) on 10-08-2003, 02:11 AM:
 
According to the Arclight Cinerama Dome webpage, the Screen in the Dome is 32x86ft. The screen is curved, so I don't know how much that makes a difference. The picture when I went (Scarface) was plenty bright, and clear.
 

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Posted by Bevan Wright (Member # 1884) on 10-08-2003, 05:52 AM:
 
John P., there has been a theory kicked around for sometime that very large screens need less light simply due to the sheer size and amount of light coming back to the viewer. [If I'm not mistaken, IMAX screens tend to get away with less light and have very satisfactory results on their massive sheets.]

Several industry experts have discussed doing some studies to prove this theory... have you heard of anyone actually going through with this activity?
 

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Posted by John Pytlak (Member # 331) on 10-08-2003, 06:04 AM:
 
I don't know of any study, but I don't subscribe to that theory. It's really the viewing angle that determines how "big" a picture appears. As you know, SMPTE 196M specifies 2 to 4 times the image height as the preferred viewing distance. Most 35mm theatres today put seats in the range of about 1 to 5 image heights. If the theory held, the people close to the screen would feel it's too bright, and the people at the back of the theatre would feel it's too dim.

Of course, IMAX and other 70mm special venue theatres have seats much closer than 1X the screen height, so maybe they are a special case.
 

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Posted by Gordon McLeod (Member # 33) on 10-08-2003, 09:34 AM:
 
Bill Shaw did tests way way back when regarding the light levels and in the beginning prints like North of Superior as such were timed for light levels around 9FL
Often more light shows off strobing more readily
 

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Posted by John Pytlak (Member # 331) on 10-08-2003, 01:01 PM:
 

quote:

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Often more light shows off strobing more readily

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