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Author Topic: Critical distance between projector in change-over booth Marin Zorica Jedi Master Film Handler Posts: 671 From: Biograd na Moru, Croatia Registered: May 2003 posted 02-22-2010 06:56 AM                     I have one booth, screen is 8m (26ft) wide for scope, distane is 26m (85ft), and projector are each by side from center 1.9m (6ft), so distance between projector are 3.8m(12ft) total. I did check on schneider software that distortion is 2%.....what you think on this? It would be okay or....also screen is flat.  |  IP: Logged Ian Parfrey Phenomenal Film Handler Posts: 1049 From: Imbil Australia 26 deg 27' 42.66" S 152 deg 42' 23.40" E Registered: Feb 2009 posted 02-22-2010 12:27 PM                     Marin. 2 % is an abstract value that I find hard to correlate with image quality. How does the picture look with some RP40? If the images on that is ok then all should be fine. At a throw of 26m, the closer together you can get the projectors the better but then you have practical issues to deal with such as risk of bumping the right hand machine when threading the left and so on. Somewhere there will be a happy medium where distortions are acceptable (if at all) and operator convenience is not compromised.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 02-22-2010 12:40 PM                     ? have you seen the spread between projectors in Brad's new booth for his screening auditorium ? ... and I bet that's not even a 50ft throw. Thus, with an 85ft throw, 12 ft isn't too bad - maybe a light case of keystoning. -Monte  |  IP: Logged Hugh McCullough Expert Film Handler Posts: 147 From: Old Coulsdon, Surrey, UK Registered: Jan 2003 posted 02-22-2010 05:04 PM                        In the UK, irrespective of the length of throw, the recommended distance between change over projectors is 4ft 6ins, about 1.4 metres. This is measured from the optical centre of projector 1 to the optical centre of projector 2.  |  IP: Logged Marin Zorica Jedi Master Film Handler Posts: 671 From: Biograd na Moru, Croatia Registered: May 2003 posted 02-22-2010 05:08 PM                     That's 2.8 meter from both projector, we have here about 1.8 to 2m mostly....well the less the better and less space As, screen is smaller and distance is higher, the distortion is less...  |  IP: Logged Brian Guckian Jedi Master Film Handler Posts: 594 From: Dublin, Ireland Registered: Apr 2003 posted 02-23-2010 01:38 PM                     quote: Marin Zorica I did check on schneider software that distortion is 2%.....what you think on this? It would be okay or....also screen is flat. Yes, it's OK. The horizontal offset from the screen centreline of each projector appears to be 4.18 degrees approx., calculated thus: Inverse Tan 1.9 / 26 = 4.18 degrees The usual rule of thumb is to keep the offset under 5 degrees maximum. This is only a coarse measure and the distortion equations are far better - 2% is very good (3% is usually the maximum preferred value, and not to exceed 5%). It also looks as if you could accomodate another machine in a central position, based on your information.  |  IP: Logged Jim Cassedy Phenomenal Film Handler Posts: 1661 From: San Francisco, CA Registered: Dec 2006 posted 02-23-2010 05:04 PM                     The old "Mitchell's Projection Manuals" had a simple formula for determining recommended spacing between dual projectors based on the distance to the screen. Unfortunately, I can't seem to find my manual at the moment so I can't look up the info for you, but I'm sure someone else on the forum probably has one of these books and can look it up.  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 02-23-2010 09:14 PM                     Monte, it also required quite a bit of custom modification to the projectors to keep the entire image in focus.  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 02-23-2010 09:29 PM                        In case anyone cares: The old SMPTE projection book has a diagram which specifies 72" from lens center to lens center. Massachusetts code requires 42" clearance on each side and rear of each projector, although it is not clear if the spaces can overlap. (I assume that this is allowable, as I have never seen a booth with 84" of space between the projectors.) One annoying "feature" of at least two newish (last few years) installations in this area is the placement of a video projector between the 35mm projectors. I can almost understand why this was done, but it rubs me the wrong way to think that film presentation is being compromised for the sake of video.  |  IP: Logged Marin Zorica Jedi Master Film Handler Posts: 671 From: Biograd na Moru, Croatia Registered: May 2003 posted 02-24-2010 05:02 AM                     quote: Brad Miller Monte, it also required quite a bit of custom modification to the projectors to keep the entire image in focus. Can you tell us a bit more detail? You thinking on adjusting lenses a bit, or film path in gates?  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 02-24-2010 11:11 AM                     Lens holder and gate had to be skewed.  |  IP: Logged

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