Film-Tech Forum ARCHIVE: Need Advice For a Problem

This is topic Need Advice For a Problem in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=004761

Posted by Jack Culpepper (Member # 724) on 04-07-2003, 09:55 AM:

Situation: In my home theater I have a Simplex XL setup. The projector throw is 25ft. The lamphouse is an ORC model 2500. The lamp inside is a Canrad-Hanovia 1.6 kw. When the lamp is on, it draws approx. 47 amps.

The screen is homemade. It is made of sheetrock painted with the whitest paint I could find. The image area on th screen measures 53 in. X 125 in. Masking is black felt.

Problem: When the film is projected on he screen, the image does not seem as bright as it should. Bright, sunny daylight scenes seem dim. I have adjusted the reflector every way I can, but no improvement. Ihave no dea how many hours are on the bulb.
Any information, advice, suggestions, etc. would be most appreciated.

Posted by Mike Rendall (Member # 1499) on 04-07-2003, 10:10 AM:

Is the reflector clean or tarnished? Is the lens clean or tarnished (has it broken down inside?) Does the lamp have dark spots on the envelope - has it been turned recently (horizontal burners) Do you have another lamp that you could try? Do the electrodes look OK on the lamp. I don't personally know anything about your lamphouse or brand of lamps, but these are the things that I would start looking at first.

Mike

[Note :
The notes below come from notes I made when a theatre tech aligned a new lamphouse in our theatre - they are here for possible help and guidance since it is unlikely that many projectionists will have the tools.]

To align the lamp with the screen we have a special lens mount that a rod can be fitted, this then goes through the shutter (switched off) to the base of the lamp (horizontal burners only and lamp removed) This should be aligned perfectly to ensure that the end of the lamp is facing the centre of the film and hence the lens. This only really needs doing when the theatre is set up or when significant changes are made after.

When this is sorted you know that the lamp is approximately correct. If the bar is removed then the adjustment of the reflector can be made, projecting the white light through the lensholder (now with the bar removed) the relfector can be positioned such to give an even spread of light (you will see a black circle in the middle (this is the end of the lamp)).

If the lens is replaced you should get an even spread of light across the screen.

Posted by Dustin Mitchell (Member # 372) on 04-07-2003, 11:18 AM:

I know that all lamphouses have different specs, but 47 amps seems awfully low for a 1600 watt bulb. Our 1600 watts in Strong Super Lume-x lamphouses draw between 65 and 70 amps.

Posted by Daryl C. W. O'Shea (Member # 1303) on 04-07-2003, 11:46 AM:

'Ditto' on the current. 47 amps is way too low. I usually run 1600 watt lamps between 60 and 68 amps. At 47 amps the lamp would be operating at roughly 70% of its rated current.

Posted by Mark Gulbrandsen (Member # 72) on 04-07-2003, 11:51 AM:

You need to be sure that the rectifier you are using with the 2500 can supply that much steady state current. If you have an ORC 1kw rectifier on it you won't be able to run a 1600 watt lamp at the proper current. You may want to get a real screen if this is the case and get a pearl finish screen as they have better contrast, more snap to the image, and a brighter overall image. With all the funds spent on everything elsen you seme to have somewhat cheated yourself on the screen end of things.
Mark

Posted by John Pytlak (Member # 331) on 04-07-2003, 11:51 AM:

Have you actually MEASURED the screen luminance?

http://www.kodak.com/US/en/motion/newsletters/pytlak/spring98.shtml

http://www.kodak.com/US/en/motion/newsletters/pytlak/june2000.shtml

http://www.kodak.com/US/en/motion/newsletters/pytlak/oct2001.shtml

http://www.kodak.com/US/en/motion/newsletters/pytlak/march2000.shtml

For that size image on a matte white screen, you should have plenty of light, so there may be a problem somewhere in the light path or alignment. More details on the shutter, lens, etc. would help diagnose.

Posted by Adam Martin (Member # 641) on 04-07-2003, 02:05 PM:

Please edit the thread title in the original post to something useful, like "Dim lamp in home theater". Everybody "Needs Advice For a Problem". [Smile]