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Author Topic: where best to put filters to "stop down" the light Alan Gouger Jedi Master Film Handler Posts: 501 From: Bradenton, FL, USA Registered: Jul 2000 posted 04-08-2008 09:02 AM                        I am enjoying this thread. I thought Xenon always threw the proper color temp never thinking reflectors etc could shift the color. I recently installed a small 500watt Kneisley lamphouse and compared to my other xenon lamp house it has a very greenish blue tint to it. The reflector is glass. Im guessing its the reflector responsible for the tint? Is there differences in color temperature between lamps as well?  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 04-09-2008 08:06 PM                        I have seen a number of discussion on here about color matching reflectors and that it is fairly critical (and difficult) to get them perfect. But that has always been in reference to xenon lamphouses. Is that peculiar to xenon only? I have not heard that in reference to carbon arc. Is carbon arc less prone to variations in the reflectors?  |  IP: Logged Paul Mayer Oh get out of it Melvin, before it pulls you under! Posts: 3836 From: Albuquerque, NM Registered: Feb 2000 posted 04-09-2008 10:17 PM                        The one time I had to match up a pair of dissimilar lamphouses I taped the color correction filters (1/4 CTO on that particular job) to the backside of the shutter housing (Simplex XL). That way I didn't have to project an image through them. That booth also did not have any glass in the projector ports, which kept the DP from claiming I was "loosing it in the glass." As has been noted elsewhere on these forums probably the easiest (if not cheapest) way to get matched color performance is to order reflectors that come from the same manufacturing batch. As for intensity I thought most modern lenses have a provision for installing stop down rings as needed for each format to be shown.  |  IP: Logged Richard P. May Expert Film Handler Posts: 243 From: Los Angeles, CA Registered: Jan 2006 posted 04-10-2008 10:17 AM                     Frank, It's been a long time since I've used carbon arcs, but remember the color could change based on whether they were properly trimmed or not. Often changeovers showed a difference, especially on B&W films. Wouldn't this make it particularly hard to balance the lamps? RPM  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 04-10-2008 12:45 PM                        No doubt the color can change due to trim, but more than that, it changes with the temperature of the rods themselves. The trick is to fire up the incoming lamphouse a few minutes before the change-over. And no question, B&W films is where you see the color temp variation the easiest. With color film, especially when change-over is between scenes where there is little reference information for the eye, it is very difficult for the average person not looking for variation to tell color temp change. If you start your arc 4 or 5 minutes prior to change-over, the plazma gets the rest of the rods behind the arc hot enough so as to reach the same temp as the outgoing machine. Color between the two then are very close. We also keep the rods in the lamphouse itself so the constant heat in the lamphouse helps pre-heat them enough so as to drive out any moisture in the carbon itself. We still run carbon arcs....probably will until we can no longer get the carbon rods. Never saw any reason to change as it is not an automated booth. And that nice big fat arc that carbons generate makes it really easy to get very even illumination across the screen, edge to edge.  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 04-12-2008 10:26 AM                       quote: Frank Angel it changes with the temperature of the rods themselves.... the plazma gets the rest of the rods behind the arc hot enough They're not rods, they're carbons.  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 04-12-2008 10:38 AM                        So, Frank, where do you get your reflectors and do you have a problem with cracking? I know of one theatre that may have to convert to xenon due to the lack of a reliable source for reflectors.  |  IP: Logged Bernie Anderson Jr Master Film Handler Posts: 435 From: Woodbridge, New Jersey Registered: Apr 2000 posted 04-12-2008 09:30 PM                        Wouldn't a 3 bladed shutter do the same thing? This is the first I'm hearing of the filter idea. I get alot of shutter flicker on my scope too being its a small screening room and a filter sounds like a great idea.  |  IP: Logged Richard P. May Expert Film Handler Posts: 243 From: Los Angeles, CA Registered: Jan 2006 posted 04-13-2008 01:00 PM                     A 3-bladed shutter could very well cut down the light. The Norelcos have a 1-bladed shutter. Probably a replacement shutter could be custom made with a larger blade, but changing it would eliminate the flexibility of modifying the light if needed, such as when running scope films.  |  IP: Logged Bernie Anderson Jr Master Film Handler Posts: 435 From: Woodbridge, New Jersey Registered: Apr 2000 posted 04-13-2008 06:22 PM                        After reading this thread, I decided to take out my three bladed shutter and try it again. I remember now why I removed it. For some reason, I can't get shutter ghosts out of it, even with the fine adjustment (Super Simplex). If I clear up the top, the bottom starts to ghost and so on. Its as if the blades are just a hair to small to cover the movement of the film. I still get flicker and its only on the right side of the screen. Its not as bad as the 2 blade, but even with the 2 blade, I get more flicker on the right side of the screen than the left. Before anyone says anything, the power supply was rebuilt with new diodes and caps and they work and its focused and aligned properly. So its definitely something to do with the shutter. Now my question is with the filters, what kind of filters are they? The Schneider Filters will not work, but the gel filters sound like they're a stage lamp filter used for stage work. If so, does anyone have the color number? And if this something that should be before the aperture? Or can it go between the aperture and the lens? Bernie  |  IP: Logged Adrian Hauser Film Handler Posts: 44 From: Sydney Registered: Mar 2008 posted 04-13-2008 10:38 PM                        OUr engineer is making up some glass "filter packs" to put in front of the Lenses. They are Color Correction filters to be matched to each lens. Does anyone know of how to measure the rating/intensity of the light out put and convert that into a heat value, so that we can make sure we get the right specced glass. Ie that wont crack! OUr lamp is a 1k xenon. If we can put it before the film plane I guess from comments here it would be better, but I guess then the light is even hotter. The corrections are quite minimal ie:6300k to 5800k. ADrian  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 04-14-2008 11:02 PM                        Scott, luckily, when I first got to this theatre, I was a young snot nosed kid and I overdid everything. I told them to get literally a closet full of carbons and 5 sets of reflectors. Only recently I had to get more carbons, and only changed reflectors twice because of some kind of caustic goop that dripped down from the exhaust pipe when rain water blew into the intake vent. quote: Tim Reed They're not rods, they're carbons. Well, perhaps, but both work for me and both are technically correct. "Carbons" : the name assigned the specific functioning of a part in the arc lighting system; it derives from the main functioning component -- carbon, similar to the way "intermittent" is assigned to a specific functioning gear system to advance the film. If you said, the "film advancing gear system," you would still be correct. Similarly, you can also refer to carbons in their more generic term which describes the part itself, i.e., carbon compressed and surrounded by a copper sheath (in some) in the form of a ROD -- hence, carbon rods. Perfectly understandable....it communicates what is intended and it's technically correct. (How's that....did I wiggle my way out of that one?)  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 04-16-2008 03:04 PM                       They are not called rods, they're called carbons. Ask any old timer.  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 04-16-2008 07:42 PM                     A welder would call them "rods"  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 04-16-2008 11:48 PM                        Are you saying I am not an old timer? Tim, you're too too kind!  |  IP: Logged

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