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Author Topic: Black Shadow On Flat Films. Brandon Lokesak Film Handler Posts: 34 From: Johnstown, PA USA Registered: Mar 2004 posted 06-24-2004 01:16 PM                     Alright I know I posted this before but i never really got an answer and I messed around alittle bit more and got some new results. I posted before that on my flat films there is always a shadow or darker area on the left and right sides running top to bottom I filed the plate but they are still there however when i have just the bulb running and no film in i can get rid of the shadows by turning the focus knob it makes the bulb area so crisp but when the film is threaded the film is way out of focus. Any Ideas here? Its a cinemecannica 2000 watt lamphouse with a century sa its not the bulb because we have tried other bulbs with the same problem. Thanks in advance.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 06-24-2004 01:32 PM                    You need to run a test loop with the aperture plate removed to make sure that the correct part of the image is filling the appropriate area of the screen, in other words checking the projector aim, the lens focal length, lens mount alignment, and the screen masking. If those are correct and the picture looks okay projecting with no plate (not counting the excess spill of the picture beyond the screen) and putting the plate back in causes shadows then you do need to file it out. But if you cannot project a proper picture without the plate (again, the spill not withstanding) then don't touch the plate and work on fixing whatever really is wrong. Isn't that what you were told the last time?  |  IP: Logged Darryl Spicer Film God Posts: 3250 From: Lexington, KY, USA Registered: Dec 2000 posted 06-24-2004 01:56 PM                    quote: Brandon Lokesak however when i have just the bulb running and no film in i can get rid of the shadows by turning the focus knob it makes the bulb area so crisp but when the film is threaded the film is way out of focus. Any Ideas here? your are focusing the aperture when you do that. The edges of the plate become sharp in focus. That is why you are out of focus for the film. Check your bulb focus spread using the scope lens. Make sure the light is evenly spread accross the screen.  |  IP: Logged Peter Mork Expert Film Handler Posts: 181 From: Newton, MA, USA Registered: Jun 2002 posted 06-24-2004 03:47 PM                     Anothe thought - is there a screw-on tube at the front of the lens that might be blocking some of the light? This has been known to happen. Replace any tube with a shorter one and see if it makes a difference.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 06-24-2004 06:19 PM                     Could this be vignetting due to optical centerline of the lens being mis-aligned (especially with an extremely short focal point lens?) Is there a chance the project beam is being clipped as it goes out the porthole? Is is possible that the aperature place is screwed up. I agree - time to run some alignment test film. There is umpteen things that can cause the problem.  |  IP: Logged Brandon Lokesak Film Handler Posts: 34 From: Johnstown, PA USA Registered: Mar 2004 posted 06-24-2004 07:23 PM                     When I filed the apature i took only a little bit off and u could see a faint line from the soundbar but the shadow was still there so i dont think that it is the apature plate. The image isnt being clipped off by the port window to my knowledge because u can still see the picture its not really completely black its just a shadow in a way. I got one theatre pretty close but not perfect by moving the lens back in the lens mount a bit but that doesnt make any sense to me because thats just focusing it with out turning the knob. Thanks for all the help im getting this time around.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 06-24-2004 10:03 PM                     What is the throw and lens size? Kill the xenon lamp, wait about 5 seconds or so and look down the barrel. You might see something. How much area does the projected light cover on the final element of the lens? What kind of projector, and what kind of xenon?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 06-24-2004 10:49 PM                     Take the apperture out and see if the shadow is gone if it is then it is the culprit and its edges will have to be delt with If it is still there then it is something else  |  IP: Logged Mike Pennell Expert Film Handler Posts: 150 From: Tucson, AZ, USA Registered: Apr 2003 posted 06-24-2004 10:50 PM                     Its possible it might be the actual gate thats causing the shadow. Pull out the aperture with a white screen and see if the shadow is still there. If it is remove the gate/trap and see if its still there. If it isnt, for some reason ive seen the light clip the metal of the hole that leads to the aperture itself.  |  IP: Logged Dominic Espinosa Phenomenal Film Handler Posts: 1172 From: Boulder Creek, CA. Registered: Jan 2004 posted 06-25-2004 03:26 AM                     It's obvious, but I figure it oughta be pointed out anyway... Whenever you're diddling with your bulb with no film in the gate make sure to close your dowser every 30 seconds or so so as not to crack the lens. It's not a pretty picture. (Pun intended.)  |  IP: Logged Mitchell Dvoskin Phenomenal Film Handler Posts: 1869 From: West Milford, NJ, USA Registered: Jan 2001 posted 06-25-2004 07:49 AM                     Working with a lot of small screening rooms, I frequently see this problem with short focal length lenses, specifically under 2.75" lenes. The problem is caused by the lens being so far back toward the gate that it picks up the little bit of ambiant light that is visable around the aperture plate cutout. If the film was right up against the plate, this would not happen, but that can not be, otherwise the plate would scratch the film. I Never did find a solution for this, other than bringing in the masking a little to cover it. /Mitchell  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 06-25-2004 09:32 AM                     That is one of the advantages of the small lens that Zeis placed directly behind the apperture was to convert the cone of light into parrallel light. It matched the projection lens and greatly improved sharpness and contrast and light transmision Meo still uses them on their projectors  |  IP: Logged Christos Mitsakis Expert Film Handler Posts: 242 From: Ag.Paraskevi, ATHENS, GREECE Registered: Sep 1999 posted 06-26-2004 11:32 AM                     Brandon, Have you checked if the working distance of the mirror to the film gate it is to lamphouse specs? Also is it a vertical or horizontal lamphouse? C.  |  IP: Logged Christos Mitsakis Expert Film Handler Posts: 242 From: Ag.Paraskevi, ATHENS, GREECE Registered: Sep 1999 posted 06-26-2004 11:32 AM                     oops mistake. C.  |  IP: Logged Ron Keillor Expert Film Handler Posts: 166 From: Vancouver, B.C. Canada Registered: Jul 2003 posted 06-26-2004 08:46 PM                     It would be useful to know the width of the shadow on the screen. At Oakridge there is a distinct lack of reflectivity on one side of the screen in theatre 3 when showing 'Scope which matches the width of the masking when brought out for 'flat' pictures, as if the surface might have been abraded or there have been a chemical interaction between the masking material and the screen surface.  |  IP: Logged

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