Film-Tech Forum ARCHIVE: anyone using the new Harkness Hall P1M (microperfored 0.5mm) screen ?

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Posted by David Baum (Member # 568) on 11-23-2000, 07:51 PM:

hi

how is it ( gain, color accuracy, does the front speakers need much equalization compared to the 1.2mm perfored models ?).

thanks
David

Posted by Brad Miller (Member # 2) on 11-24-2000, 01:43 AM:

While the subject of Harkness screens is up and running, has anyone used the Spectral 2000 silver screen surface?

Posted by Gordon McLeod (Member # 33) on 11-24-2000, 08:15 AM:

All my rep theatre installations have used the spectral2000 and find it excellent

Posted by Barry Hans (Member # 477) on 11-24-2000, 02:02 PM:

We just installed a Spectral 2000 screen last weekend and it is GREAT! Looks as if we jumped up a bulb size or two! Well worth the high price.

Posted by Alan Lyman (Member # 557) on 11-27-2000, 04:55 AM:

Shouldn´t the Silverbased screens only be used for 3D films,or can this type of screen in particular,also be used for normal filmprojection?

Posted by Gordon McLeod (Member # 33) on 11-27-2000, 07:01 AM:

Silver Based screens can be used for all types of projection But they are highly directional so wide viewing angles must be avoided due to the light falloff that occurs

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

SMPTE Recommended Practice RP 95 specifies "Installation of Gain Screens". Because a gain screen is directional, and acts somewhat like a mirror, it needs to be properly curved to reflect the projector's light back to the center of the audience. Ideally, this is done by ray tracing (angle of incidence = angle of reflection), but some simple "rules of thumb" are sometimes used to choose the proper screen radius and angle of tilt.

RP 95 suggests the radius of the screen curvature should be (Projection distance + Distance Between the screen and audience center) / 2. So if the throw is 100 feet, and the center of the audience is 50 feet from the screen, the radius of the screen curvature should be (100 + 50) / 2 = 75 feet.

Matte white screens should always be installed "flat". But unless gain screens have the proper curvature, getting uniform illumination throughout the auditorium will be difficult.

------------------
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 Brad Miller (Member # 2) on 11-28-2000, 04:54 PM:

"Matte white screens should always be installed "flat"."

Well, you've got a few people to tell about that little tidbit!

I hate curved screens in all aspects. Every curved screen I've ever seen (even AMC's compound curved ones) causes geometric distortions of the image. I do not like the THX Broadway rectangle "smiling" at me and every tall building "leaning" inward!

Posted by Rory Burke (Member # 512) on 11-28-2000, 05:41 PM:

Brad M

I believe SMPTE also has a standard for distortion of the screen image as well...and if some theater chains followed the proper procedures to with in tolerable levels that might not occur as often.... but true enough in a way, that THX broadway trailer "blue box" points to you off the bat if your aperature plate is cut improperly or if there is too much upward angle of the screen as seen in some stadium theaters, venietting etc etc. I kind of like that blue box cause it keeps procetionists honest when framming their picture as well. And how many times have I noticed the surrounds swapped during the TEX trailer as he flys around the auditorium. OUCH!!! Some one should come out with a trailer that intentionally, while entertaining the audience, does a quick Channel ID and picture format check. As a matter of fact I wouldn't doubt if that was part of the original intent of the THX Broadway trailer.

Rory

Posted by Dave Bird (Member # 490) on 11-28-2000, 07:20 PM:

Weren't curved screens really intended for special formats like Cinerama and IMAX? Isn't the only reason they install them now for the gimmicky publicity "with giant wall-to-wall CURVED screens"? (No matter the presentation.) What was the aspect ratio of Cinerama? Some of those outdoor screens were absolute beasts!

Posted by Gordon McLeod (Member # 33) on 11-28-2000, 08:03 PM:

When done properley a curved gain screen will exhibit a flatter light light field and better overall focus
If not done properley then that is another story

Posted by Brad Miller (Member # 2) on 11-28-2000, 09:56 PM:

Gordon,

Please point me to one done properly. I'd like to see it. At a previous screening room I had set up, I took a string with a Sharpie marker on one end and the other end tied to the aperture and drew lines on the walls where the screen was to go (all 4 sides) and I was wholly unimpressed with the result and "bent straight lines" was annoying as always. The projector was not at any vertical angle either nor was in a position for horizontal keystoning. Now how much more accurate can you get than with a string???

That curved screen was replaced a few weeks later with a FLAT screen and I noticed no distortion whatsoever, focus was razor sharp corner to corner and although I didn't measure the difference with a light meter, I was well satisfied with the light dispersion on the flat screen.

I think Dave Bird put it best a couple of posts above, curved screens are an advertising gimmick for 35mm presentations.

Rory,

Be careful with the older "Dolby A" versions of the THX Broadway trailer, they were printed significantly high in frame! The old "DTS only" versions were the same way. The "SRD only" and "SDDS only" and the new "multi track" Broadways are the only ones properly centered in frame.

Posted by John Pytlak (Member # 331) on 11-29-2000, 06:33 AM:

Matte white (gain=1) screens should NOT be curved. High gain screens installed in relatively wide auditoriums SHOULD be curved, per SMPTE Recommended Practive RP 95. Ideally, the curve should be optimized by ray tracing, to reflect the light back to the center of the audience. But the "rule of thumb" curve of having a radius of (Projection distance + Distance between screen and audience center) / 2 is NOT a deeply curved screen, and should not cause a major problem with distortion or focus uniformity.

Deeply curved screens were used for Cinerama and D-150, the idea being to "surround" the audience and engage their peripheral vision. Distortion was an issue, especially in seats away from the "sweet spot" of the auditorium.

Posted by Dick Vaughan (Member # 540) on 11-29-2000, 07:53 AM:

Dave
Cinerama aspect ratio is 2.72:1

For details of our Cinerama installation see http://www.comp.brad.ac.uk/research/GIP/film.html

All the best

Dick vaughan

Posted by Frank Prete (Member # 627) on 11-29-2000, 04:02 PM:

Brad,

Unfortunate that you haven't seen any curved screens that look good. I can think of plenty that not only look good as you enter the auditorium, but look great once the show starts.

Next time your in Australia, I'll show you a few of my favourites which are sure to change your opinion.

Getting back to the original question, I am yet to see any micro-perf screens yet, but I am wondering if cinemas are starting to install them to be ready for 'digital' cinema?

Frank.

Posted by Brad Miller (Member # 2) on 11-30-2000, 02:06 AM:

Since I don't think I will be in Australia any time soon, someone please direct me to a properly installed curved screen in the Dallas or Denver area. I'll check it out and post my findings.

Posted by Dave Bird (Member # 490) on 11-30-2000, 06:54 AM:

There used to be a process for painting outdoor CURVED screens for gain by painting them silver, then a light spray of white, not quite covering all the silver. Recently, I've heard a couple drive-ins described as having a very dull picture, moreso than usual. One screen is curved (not many of those around), one is corrugated. Is it possible that over the years, the proper process of painting was either lost or ignored for cost reasons and painted matte white like all the other flat screens?

Posted by John Pytlak (Member # 331) on 11-30-2000, 07:34 AM:

The problem with curving a matte (gain=1) surface is cross-reflections. Since a matte surface reflects light in all directions, curving it reflects some light across the curve of the screen, reducing contrast.

A high gain screen is very directional, acting somewhat like a mirror in its reflection pattern. So it needs to be curved to reflect light toward the center of the audience, or the illumination uniformity will be poor. But because gain screens are so directional, contrast-reducing cross-reflections are much less of a problem.

The screen manufacturers use proprietary coatings to make "gain" screens like the Spectral or Perlux. Using a combination of metallic and white paints on a drive-in screen may simulate these coatings, but I suspect it would have been hard to control the gain precisely or uniformly.

Posted by Stefan Scholz (Member # 147) on 11-30-2000, 10:57 AM:

I agree with John. Reflective screen surface must be curved, as it acts like a mirror in reflection. Flat mounted the light distribution would not be even. The recommended practise specifies a light curvature only, not one of those deeply curves which require specially made prints.
Go and draw the reflective lines (incomming = outgoig agle) ad yo'll know why the RP standard is there.

Posted by John Pytlak (Member # 331) on 11-30-2000, 11:36 AM:

David Baum originally asked about the Harkness Hall MP screens. (microperforated 0.5mm screen)

AFAIK, the MP screens with 0.5mm perfs were originally developed especially for Digital Cinema applications, where the projected pixels created a very objectionable moire (interference) pattern with the 1.2mm perforations of regular screens.

According to Harkness Hall's product data, the regular screens have 1.2mm perforations, occupying about 5.3% of the screen area. Sound attenuation is about 2dB per octave above 2KHz.

The MP screens have 0.5mm perforations,occupying about 1.8% of the screen area. Sound attenuation is about 4dB per octave above 2KHz.

The smaller perfs of the MP screens should be less prone to form objectionable moire with Digital Cinema. The smaller holes also should be less visible from the front rows of seats (not that anyone should sit that close for today's Digital Cinema ). The smaller area occupied by the MP perfs should be a bit more efficient for reflection. But substantial equalization is needed to compensate for the much greater high frequency sound attenuation.

Kodak purchased a 25 x 64 foot Harkness Hall Matt White Plus MP screen for our projection lab in the 2000-seat "Theater on the Ridge" in Rochester, that is often used for "side-by-side" projection comparisons. We needed an efficient matte white surface designed for very close viewing. The new screen is installed "flat", and the frame is able to be "flown" for live stage shows.

Lots of information on the Harkness Hall website:
http://www.harknesshall.com

Posted by David Baum (Member # 568) on 12-11-2000, 07:08 PM:

oops, was away, noticed so many posts and extended discussion thanks to Brad Miller. Very interesting. Was not such aware of the curvature and mat screens incompatibility.
Thanks John for the last post on the Harkness Hall. How close can you sit in front of the 0.5mm screen ? As stated, this is for my home theater (and I still have to get a reply from H Hall about the curving metallic structure they provide, absolutely no idea on the price).
Oh, if by any chance any of you guys go to Belgium, I recommand you visit the IMAGIBRAINE THX complex in the south of Brussels: very very well done complex, excellent sound, excellent images. only 10 theaters but really well maintained ( complex is new, maybe 3 years old or something ).
regards
PS: Hi John ! ( QSC ). btw, all Kinepolis group will switch to 100. QSC DCA amps.

Posted by Richard Hamilton (Member # 321) on 12-11-2000, 08:17 PM:

Hey Brad,

How about a "Suck Screen"?

Rick

Posted by James R. Hammonds, Jr (Member # 673) on 12-11-2000, 09:52 PM:

are there certain silver screens that are able to direct light evenly in al directions or are they all that way at wide angles.
the theatre im at now has silver and they look absolotely horrible.
i dont know what kind they are, so maybe their just the bad kind.
i dont know what kind they are, butwe just had one replaced in one of our theatres, and it still looks the same.
i dont know why they didnt take that into consideration when they replaced it.
the only way to watch the movie and have it look good is to watch it from the booth.
but i dont think we can fit 200 people in the booth for one show.
maybe we could if people were made out of shrinky dinks, but their not, so there goes that.

Posted by Brad Miller (Member # 2) on 12-12-2000, 04:15 AM:

Richard,

Screens that "suck" are exactly that. They also help to make for a nice gymnasium-sounding acoustical environment.

By the way, is anyone still putting those in new complexes as of late?

Posted by David Kilderry (Member # 142) on 12-12-2000, 05:50 PM:

There are curved screens and then there are CURVED screens!

Many of todays modern screens here have a very slight curve and use Perlux screens, the results are very good.

MGM drive-ins here in Australia used giant 110ft plus curved screens at their twin drive-ins. The effect was amazing. (See Clayton page at www.drive-insdownunder.com.au)

Until the late 1980's Hoyts still operated a few deep curved strip screens for Cinerama presentations (later 70mm stuff). These were built in 1969 in anticipation of D-150 and single lens Cinerama continuing.

All you needed was a little bit of keystoning on a deep curve strip screen and a horizon shot in wide angle was all over the place. Still I recall seeing Star Wars and many other 70mm blowups on these screens and the results were pleasing - at least to a teenager.

David

Posted by David Kilderry (Member # 142) on 12-12-2000, 05:52 PM:

OOOOOOPPPPPPs!

Try www.drive-insdownunder.com.au

Posted by Brad Miller (Member # 2) on 12-12-2000, 05:54 PM:

When listing a link to another website, there MUST be a blank space immediately before and after the URL. For example, I cannot put a comma after www.film-tech.com, or it will add the comma to the link. Instead, I must type it in as www.film-tech.com , and THEN it works nicely.

Posted by David Kilderry (Member # 142) on 12-13-2000, 02:44 AM:

Thanks Brad,

I realised that a split second after I hit "post reply"!

David

Posted by Brad Miller (Member # 2) on 12-13-2000, 04:08 AM:

You can also edit a post to correct typos and such. Just click the "edit" button.