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

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Projector's motor casts a shadow...can a Magnacom help?

Author Topic: Projector's motor casts a shadow...can a Magnacom help? Jon Miller Jedi Master Film Handler Posts: 973 From: San Diego, CA, USA Registered: Sep 1999 posted 11-09-2003 08:39 PM                     I got a request for assistance from a former colleague who recently opened a theatre in Iran (!). He is running a pair of Fedi XI T-35s in a small auditorium with a fairly large screen and has noticed the projector's motor casts a shadow on the image. From his description, the motor is mounted perpendicular to the projector front, like the motor on an old Simplex or RCA soundhead, but positioned higher up. The auditorium specs are... Throw distance: 14.1m (about 46-1/4') Screen dimensions: 14.1m x 7m (about 46-1/4' x 23') I could not get an exact answer on the lenses or aperture plates used when the problem occurs, but he did mention the lenses are in the 22-25mm FL range. Also, I have no information on the kind of masking used (or if any masking is used at all). If he used a lens one notch longer than the recommended FL for a particular aspect ratio and a Magnacom to blow up the image to the desired size, will that overcome the shadow problem or will that introduce other problems, other than some light loss? Also...does anyone have any pictures of a Fedi XI T-35 so I can see how the motor is positioned? Thanks!  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 11-09-2003 09:41 PM                     A few more questions: Does the image have motor shadow in scope or just flat? Or both? Is there enough space from the present lens to the port glass for the extra length of a magnacom? I believe that the magnacom will not work with just a small variance of focal length, it is more suited to having the scope backup become the 1:85 lens by adding the magnacom.  |  IP: Logged Jon Miller Jedi Master Film Handler Posts: 973 From: San Diego, CA, USA Registered: Sep 1999 posted 11-09-2003 10:28 PM                     To answer your questions, Kenneth, the shadow only occurs in flat (either 1.85:1 or 1.66:1) and, yes, there is enough room to accommodate a Magnacom.  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 11-10-2003 12:31 AM                     Do you mean that the motor is actually getting into the projected beam? Or, do you mean there is stray light coming from the lens and reflecting on the screen? If it's the second, I would recommend using "Cinefoil" and some black gaffer's tape to block the stray light. Cinefoil is basically a sheet of heavy aluminum foil that has been painted (or anodized?) flat black. You can use it for virtually any situation where you want to block light from interfering. Stage electricians use it to fashion makeshift "barn doors" and things like that. Cinefoil is made by Rosco. Click Here for more info. It comes in rolls, similar to what household aluminum foil comes in. I recollect the cost is about $20 per roll. Black Gaffer's tape can be had from Permacel. Click Here for more info. Again, I believe cost is about $20 per roll. (Depending on your relationship with your dealer... I've bought Gaff tape for $12 - $15 per roll in case-quantities.) Although Gaff tape is made by many companies, "Permacel" is starting to become the "Kleenex" of the stage & screen industry. Many people say, "Hand me that roll of Permecel.", when they want tape just as people say, "Give me a Kleenex.", when they want a facial tissue. I tend to prefer "Pro-Gaff", myself. Permacel doesn't seem to be as sticky as "Pro-Gaff". "Entertainment Industry Tape" seems to be stickier, yet, but it also leaves more stick-um residue behind when it's removed. Pro-Gaff is more of a happy medium.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-10-2003 01:01 AM                     The much maligned Magna-Com is an excellent tool that does NOT eat up light. Believe it or not, even THEY have evolved. There are now two different versions offered by ISCO (just the one offered by Schneider). ISCO even stopped using the "MagnaCom" name and calls them Zoom Converters. With a 47.5mm lens and the ISCO zoom converter type "S" you are only going to get down to a nominal 31mm EF. The Zoom Converter will move the focal point forward. I can't say if it will be enough. Other alternatives include an older ISCO lens design (I don't have its part number handy) but it had an EF of 31.2mm. It used a 60mm Ultra prime lens with a .52X magnifier that will move the focal point substantially forward and it looks VERY good. Once upon a time it was called a "Spezial" From Schneider you have a few options. They make EXTREMELY short focal length lenses for 1.85 projection (one is 19mm the other is slightly longer at 21mm). They are part of their "Super Wide" series of lenses. http://www.schneideroptics.com/projection/cinema_projection/super_wide/ I believe that magnifier can be used with other focal length prime lenses to obtain longer focal lengths. Also from Schneider...they have optical extensions for their lenses down to 24mm. They are essentially just a big hunk of optical glass that will move your focal point forward by a inch or two. They were brought out to stop vignetting in ordinary lens turrets. Steve [ 11-10-2003, 02:35 AM: Message edited by: Steve Guttag ]  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 11-10-2003 01:03 AM                     quote: The much maligned Magna-Com is an excellent tool that does NOT eat up light. The hell they don't! I've got several of the actual "Magna-Com" branded lenses here and they ALL eat up light as compared to a fixed focus lens that produces the same size image. You're smokin' crack, Steve. I will agree that the Schneider lenses don't eat light though. I haven't used any of the recent ISCO ones.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-10-2003 02:37 AM                     Not smokin crack...just have used them effectively and not had the light-eating issue. Steve  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 11-10-2003 09:18 AM                        Obviously, any additional "glass" will reduce light level. With proper anti-reflection coating, it shouldn't amount to more than about 5 to 10 percent less total lumens.  |  IP: Logged Jon Miller Jedi Master Film Handler Posts: 973 From: San Diego, CA, USA Registered: Sep 1999 posted 11-10-2003 07:33 PM                     Thank you all for your comments so far. (Yes, Randy, it is the motor that is casting a shadow, but it's good to know who makes that black foil just in case I need some in the future. ) A straight lens won't work...the front element is just too far back. I'm just concerned there might be some vignetting when a "zoom converter" is used with a short-focal-length prime lens. Steve, you wrote... quote: Also from Schneider...they have optical extensions for their lenses down to 24mm. They are essentially just a big hunk of optical glass that will move your focal point forward by a inch or two. All I could find on Schneider's site were two converters, but no "optical extensions." Were they discontinued recently?  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-10-2003 08:19 PM                     Nope they are there...just not listed as such...you can find them on the price sheet. Click Here for a pdf of the price sheet. Refer to page 6 in the "Adapters" section. Steve  |  IP: Logged

All times are Central (GMT -6:00)

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.