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

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Focussing Laser Subtitling (Page 1)

This topic comprises 2 pages: 1  2

Author Topic: Focussing Laser Subtitling Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 12-14-2002 02:04 AM                     Hello all again, Due to the angle of projection of the projector, laser subtitling focus is achieved only for the subtitling but the top of the picture is not fully focused. Is there a simple trick to adjust this?  |  IP: Logged Matthew Peters Expert Film Handler Posts: 179 From: Glen Waverley, Melbourne, Australia Registered: Nov 2002 posted 12-14-2002 03:40 AM                     If the term “laser subtitling focus” is the process of adding subtitles to a print for distribution in a location outside the origin after the film is made, and the subtitles are “laser” or burned-in….. I have experienced similar problems with the foreign films “The Closet” and “Amelie”, the solution our cinema took was to simply “half” focus, allowing the subtitles to be very slightly out of focus but readable and the top of the picture to also be slightly out of focus but almost unnoticeable. A sort of midway focus was all we could do, none of our patrons noticed or complained. Other members may have different ideas - Matthew  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 12-14-2002 05:06 AM                        As the laser subtitles are burnt into the film, they are farther away from the projection lens than the image surface. It is therefore not possible to 100% focus both of them. Solution: dts subtitling system.  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 12-14-2002 07:01 AM                     Hello Demetris, You are giving the answer to your question in the question itself. Due to the angle of the projector to the screen... It will be necessary to tilt the screen so that the center of the screen is perpendicular, at a right angle, to the light beam from the projector. This will also reduce the defect known as 'keystone effect' where the top and bottom of the image are not the same width. It was necessary to tilt the top of the screen backward for most old theatres where the projection room was on the third or fourth floor of the building and the stage/screen were on the first floor level. If you have access to the new Schneider Lens Program, you can see the effects of the projector height with respect to the image. The screen tilt can be adjusted accordingly in real life. Hope this will help you out. KEN  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 12-14-2002 08:51 AM                    Ken, his subtitles are out of focus because as the other responses point out that is the nature of the burned-in laser titles. I have the same problem and I have no vertical tilt at all. It would, however, be interesting to see what could be done if there were a way to tilt the lens vertically slightly to partially compensate for the focus shift and then reangle the projector to put keep the picture where it should be on the screen. I presume those with long throws and longer lenses have less of a problem with the laser titles.  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 12-14-2002 03:03 PM                     Steve, The focus system you describe was used on the camera to film the opening text of the "Star Wars" films. The camera lens is tilted at an angle to the film and renders the image in perfect focus despite the disparity of distances involved. This is called the 'Scheimpflug Principle' and is described in Kodak's Encyclopedia of Practical Photography on pp 2193, 2194. A more easily accomplished method might be to increase the F stop of the lens which will expand the overall depth of focus. You will loose light but gain depth of focus. Our old F3.5 lens was much easier to focus than the new F1.9, the reason is the depth of focus which accompanies the F rating. KEN  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 12-14-2002 11:50 PM                    More than a little light if you figure that one f-stop down cuts the light in half.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 12-15-2002 05:46 AM                        Steve, I think Demetris's problem is not the disparity between the laser etched text and the emulsion of the image; he says that only the top half of the picture is soft. If the problem were the laser etching, then the entire picture would be soft if you focused on the subtitles. The fact that only the top half is soft tends to support Ken's theory that it is a keystoning/angle problem due to the projection booth height. This is a more serious problem as it effects non-subtitled films as well. On regular films the gradation of focus probably isn't as pronounced at the very bottom of the picture because he would naturally focus at the center, not at either the top or bottom extremes. The subtitles at the extreme bottom of the image would make his keystoning focus problem more apparent. Demetris, you need to run a 35PA/RP40 test loop and check the optical system's ability to focus evenly across the entire screen. If you can't keep both the top and bottom in focus simultaniously, then you do have either an angle problem or a lens problem which should be addressed. Ken's solution of tilting the screen will work if it a keystoning problem, but that's more easily said that done in a lot of physical setups. In the old single screen theatres like one that I work in, where the screen assembly is on a fly system, tilting the screen is a piece of cake -- most of the Brandt theatres on 42nd in Manhattan all had their screens tilted to compensate for the severe projection angle (many of those booths were five stories above the stage floor). But in many modern multiplex setups, the screen frames are bolted to the walls and it would take much more finagling to tilt them accurately. If you don't have a steep projection angle, and you see from the test loop that you can't maintain even focus, then I would suspect either the lens turret/mount, or the lens itself as being the culprit. Frank  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 12-15-2002 07:38 AM                     Well, Actually, the picture is fully focused if the subtitling is not Laser. The problem is with the subtitling. The tilted screen can be a solution although it is a bit difficult due to the lack of space behind and in front of the screen since we are talking about a theater with curtains. ALSO Please note, I've been thinking about the keystone effect. What if someone installed a feature on the projector so that the apperture plate can be tilted????? In theory, that would help in removing the keystone effect. I know that some of the theaters like to carefully (cut or rub with someting that eats the apperture plate) very very slowly until they achieve a straight line on the edges of the screen. Would this work? Demetris  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 12-15-2002 10:01 AM                        Tilting the aperture plate won't fix keystoning of the image. There should be enough depth of field in typical cinema lenses to allow the image to be focused from edge to edge, corner to corner even with a relatively steep tilt angle. One idea that I've thought of but never seen implemented would be an implementation of the swing and tilt movements that are possible in a large-format view camera, but adapted to cinema projection. This would allow images to be projected perfectly square, even when the projectors aren't in perfect horizontal and vertical alignment with the screen.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 12-15-2002 10:04 AM                    The aperture plate has no bearing on image focus. What you propose might make sharper edges but these should be falling on the black masking anyway and this is of little consequence. Now, if you could slightly angle the gate and trap assembly that might be of help. But probably more practical to make some adjustment to the lens mount.  |  IP: Logged Charles Everett Phenomenal Film Handler Posts: 1470 From: New Jersey Registered: May 2001 posted 12-15-2002 01:16 PM                     Are the subtitles in a "thin" or "thick" typeface? In the US most foreign-language imports have the subtitles in a "thin" typeface that is difficult to focus on. Even the Japanese version of Spirited Away -- which Disney provided to the Loews E-Walk in NYC -- had subtitles in a "thin" typeface. US release prints of El Crimen del Padre Amaro have the subtitles in a "thick" typeface.  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 12-17-2002 06:26 AM                     Yeap, Subtitles are thin. Although some distribution companies like to put "war layers" for subtitling which focusses much easier  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 12-17-2002 07:16 AM                        Some links about subtitles: http://www.titrafilm.com/TitraEn/pagesEn/laser_subtitling.html http://www.titra.com/film.html http://www.lvt.fr/Lvt_En/index_LVT.html http://www.lvt.fr/Monal/Monal_Engraving.html  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 12-19-2002 12:37 PM                     Hello, Demetris, Could you make a few checks for me? With the image, not the subtitles sharply focused, go to the screen with a piece of cardboard and check the titles. See if the cardboard held in front of the screen can get a focused image of the letters. Also see if there are any colors around the edges of the letter images. If so, what are the colors and where do they appear? Left or right? Can you give me some idea of the distance from the screen that the subtitles are in focus? How far from the screen surface does the card have to be to make a perfect image? If the titles are "more blurry" in this test, then we will know that the titles focus plane is "behind" the screen. Since the normal optical printing of subtitles places them "in the emulsion layer" of the print, they are very likely to be in focus with the image. Laser cut subtitles remove the emulsion layer completely and therefore are in a slightly different plane than the image. Focusing the image projects the walls of the etched image less clearly. The image is sharpest at the margin between the emulsion and the film base. Perhaps a small vertical tilting of the gate could remedy this situation. A small shim placed behind the gate runner casting could make enough shift in the film plane to correct this problem. Thanks for working with me on this. KEN  |  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.