my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Digital Cinema Forum   » Projection port distance from lens. (Page 1)

This topic comprises 2 pages: 1  2

Author Topic: Projection port distance from lens. Adam Fraser Master Film Handler Posts: 499 From: Houghton Lake, MI, USA Registered: Dec 2001 posted 03-11-2015 10:46 AM                        We are working with an architect to add another screen to our theatre. We have a chance to re-use our old booth but there will be a 10 foot distance between the projector and a window in the back of the auditorium. The image will be about 2.2'x5.5' when it gets to the port in the rear of the auditorium. Any problems we need to be aware of when placing the port window so far from the lens? Who would you recommend to have make a 3'x7' port window with the proper glass. I know the window will be very expensive but should be much cheaper than making a complete cantilevered projection booth for a 80 seat auditorium.  |  IP: Logged Mitchell Dvoskin Phenomenal Film Handler Posts: 1869 From: West Milford, NJ, USA Registered: Jan 2001 posted 03-11-2015 12:10 PM                     There are certainly better qualified people on this forum than I to answer this, but from my experience the 2 issues you will face is loss of light and the image being reflected back off the glass into the lens (which creates strange visible artifacts).  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 03-11-2015 12:20 PM                     Would it be feasible to shoot through an open port if a "baffle tunnel" of sorts were created between machine and window?  |  IP: Logged Frank Cox Film God Posts: 2234 From: Melville Saskatchewan Canada Registered: Apr 2011 posted 03-11-2015 02:03 PM                        What about something along the line of a big furnace duct, open on the auditorium end and with the port glass placed on the projector's end. If you insulate it, no more sound should escape into the auditorium than usual.  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 03-11-2015 03:55 PM                     The light loss is the same whether it's a 4" square or 4'. Object or dirt on the glass look a lot worse on screen with the glass farther away though! You should use coated optical glass to reduce reflection, and that gets expensive for a 4' piece. It's better to have the glass tilted back so reflections hit the floor and don't bounce back to the screen: particularly with 3D adapters you will get weird ghost images if uncoated port glass is square to the projector. The reflection off the lens front element is magnified by the convex surface and that glass is coated - I have seen a very very dim ghost from a cross pattern off the lens with uncoated window glass parallel to the lens but it would not be an issue in a movie. I would recommend using proper coated optical glass with a tilt.  |  IP: Logged Rick Raskin Phenomenal Film Handler Posts: 1100 From: Manassas Virginia Registered: Jan 2003 posted 03-11-2015 04:47 PM                     I like Frank's idea. Simply frame in a light tunnel from the old booth wall to the theater. Place the port glass at the booth end and angle it down as Dave suggests.  |  IP: Logged Adam Fraser Master Film Handler Posts: 499 From: Houghton Lake, MI, USA Registered: Dec 2001 posted 03-11-2015 05:27 PM                        Thank you for the replies, and will run all of this by my architect. The only problem I am seeing with a light tunnel is aesthetics as it would go over our lobby and block the view of a 12' wide x 18' tall stone fireplace.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 03-11-2015 06:53 PM                     3'x7' is a heck of a port glass. But it is certainly doable. Roughly 2sqm of Amiran. It is available in the necessary format and strength, since it is used for architectucal applications as well. Depending on your supplier, it could cost you 1500-2000US$ excl. mounting/framing. There are different varieties of Amiran - make sure you get the right one - 'optiwhite'. 'Amiran' only depicts the antireflective coating. - Carsten  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 03-11-2015 09:38 PM                    Wait...are you saying the projector beam is going to be going across your open lobby and then through the giant port at the rear of the new theatre? What would keep extraneous lobby light from the theatre or am I not understanding the plan? If so this seems like a lot of trouble to keep the projector in the existing booth and if you really don't want to build a new booth for it then, as despised as it might be, maybe this is a call for a boothless setup.  |  IP: Logged Adam Fraser Master Film Handler Posts: 499 From: Houghton Lake, MI, USA Registered: Dec 2001 posted 03-11-2015 09:59 PM                        The projector has projected above an open lobby for 74 years with no extraneous light problems. What we are looking to do is twin our auditorium horizontally, while building a new booth for the front auditorium. We will now be building a rear wall to the new auditorium, and the lobby will be more of a common area than it was before. Here is a picture of the lobby in question, the portholes are on the right. The wall you see on the left will be removed and built to the roof, which would require a port window for the image to pass through.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 03-17-2015 05:49 AM                     Wow. Hard to imagine you're not getting issues with ambient light spill through a 2qm projection window. Yes, a 'light corridor' across that part will look awkward. Really no chance to get the projector over to the left area/closer to the screen? - Carsten  |  IP: Logged Rick Raskin Phenomenal Film Handler Posts: 1100 From: Manassas Virginia Registered: Jan 2003 posted 03-17-2015 04:25 PM                     How about if you periscope the image up to the ceiling and then into a light tunnel? I've seen it done in reverse where the booth was on the floor above the theater. I've also seen it done where the ports were too low and patrons in the balcony would have interfered.  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 03-17-2015 07:40 PM                       There's no good argument for any periscope. The resulting picture is always unacceptable.  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 03-18-2015 12:39 AM                     Okay... Does a guest would walk along this "hallway" until he gets to the stone fireplace then hang a left to get to his seat? The projector, in the booth, above the buffalo head shoots across the hallway and over to the screen, which is on the left? So, then, the picture shoots out of the port window, over the gap and would go through another piece of glass? Yeah, it can be done. I've seen stranger things. But I'd have to say that I'm not real hip on the picture shooting through two pieces of glass, much less one that will be hard to reach when it gets dirty. Use optical glass and angle it and, from what I can tell, it will work, though.  |  IP: Logged Mitchell Dvoskin Phenomenal Film Handler Posts: 1869 From: West Milford, NJ, USA Registered: Jan 2001 posted 03-18-2015 09:12 AM                     If you are going to spend the money to do construction, do it right. As impressive as that stone chimney is rising 2 stories up to the ceiling, ultimately your patrons are there to see the movie, not the lobby. That said, don't build the new wall up to the existing ceiling. Build it to the level just below the existing projection port holes and build a new ceiling from that wall to the port hole wall, leaving the space above it open so you can project the picture over it. I've seen this done, it works fine. I have even seen this done so that from the auditorium, the area above the lobby is made to look like a faux balcony.  |  IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1  2

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.