Film-Tech Forum ARCHIVE: Xenon slide projector as a lamphouse?

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Posted by Alejandro Lopez (Member # 2854) on 12-06-2004, 12:03 PM:

Hi you all: This is my first post here though I´ve been reading this forum daily at least for the last two years. At last I registered and I don´t really know why I didn´t before.
My question is: Is it possible to use a 750 watts xenon slide projector as a lamphouse for a portable 35mm projector? I have never seen how xenon slide projectors are inside but I suppose that there´s a similar mirror and so and if you maintain its focal distance it would work fine though I know that an slide projector aperture is bigger than a movie projector one. A friend of mine knows someone who´s intending to sell one at a reasonable price and I´d be interested on buying it if it works. I also suppose it has a built-in electronic (switched) rectifier. I d thank any information about.

Alejandro.

Posted by John Pytlak (Member # 331) on 12-06-2004, 12:15 PM:

Yes, you can use a slide projector as a "lamphouse", but alignment is critical, and even so, it will not be very efficient. The other possible problem is that angle of the beam will be different than a typical elliptical reflector used in normal lamphouses which could cause flaring or other optical issues.

Posted by Alejandro Lopez (Member # 2854) on 12-06-2004, 02:32 PM:

If it has an electronic rectifier and a proper eliptical mirror, ignitor, etc. you always can remove all and build a small lamphouse with an integrated (built-in) rectifier that could work fine, isn´t it?

Posted by John Pytlak (Member # 331) on 12-06-2004, 03:00 PM:

Sure, uniformly illuminating a 35mm movie film frame should be easier than the larger area of a 35mm slide. But why go through all the trouble of tearing apart and rebuilding the slide projector light source, when there are used motion picture lamphouses on the market? [Confused]

Posted by Alejandro Lopez (Member # 2854) on 12-06-2004, 03:14 PM:

John: The reason for that is that I don´t want to assemble a big lamphouse to a portable projectorfor transportability and esthetic reasons.

Alejandro.

Posted by Gilbert Travin (Member # 2138) on 12-07-2004, 01:59 AM:

HI !

You must use only the lamphouse of your slide projector : lense and slide trap must be removed. You can align the lamphouse on your 35 mm projector with a simple laser pointer.
You ca also use a 400 W halogen tungsten lamp with an appropriate mirror...

In any case, this work requires skill !!! [Big Grin]

Posted by Alejandro Lopez (Member # 2854) on 12-07-2004, 09:17 AM:

I upgraded my Wassmann/Köders from 230 volts 1.000 watts tugnsten lamp to a 36 volts 400 watts halogen bub with the apropiate mirror and condensers lenses for the type and size of filament of this lamp, smaller than the one used on older types and adjusting alignment on the three axis; horizontal, vertical and focus. I provided a system with screws, springs and so to do this adjustments. I think that I got the maximum luminous flux this lamp can give on traditional vertical position with an spherical mirror and condenser lenses) and the light is very evenly distributed on the screen. To get more light from this lamp I´d have to install it horizontally inside an eliptical mirror, like a xenon bulb. I have a small metal eliptical reflector (80- 90 mm diameter) from a gobo projector that I could use, but I´d have to make the lamphouse cover a little more depth. And with all this work, the colour tmperature would be the same, 3.400º K aprox., not daylight. Another option would be to use, with the spherical mirror and condenser lenses an HMI or HTI lamp. HMI and HTI bulbs up to 575 watts have a very short arc gap that could work for this purpose.

Alejandro.

Posted by Gilbert Travin (Member # 2138) on 12-08-2004, 01:51 AM:

HI Alejandro !
Your solutions for halogen lamps are good, horizontal position may be effectively possible !

I believe that HMI lamps are AC powered. At 50 Hz there are interferences between lamp light pulsation and shutter (48 Hz at 24 fps)
I believe that HMI lamps must be operated for cinema use at 400 Hz at least with an electronic power supply (there were a 16 mm Bauer projector such equipped ...)

Posted by Alejandro Lopez (Member # 2854) on 12-08-2004, 06:25 AM:

HTI and HMI lamps are almost identical though HTI type are specifically designed for projection. The electronic switched power supplies are the same too, depending on lamp voltage and wattage. They are metal hallogen arc lamps and you can find the same lamp with several denominations HMI, HTI, HMP, etc. upon their intended use (projection, stage and film/television, ilumination, disco, etc.) and their rated life. To avoid flicker, due to desincronization between mains (50 Hz on Europe) and shuter (24x2=48) frecuencies, electronic power supplies give a square wave instead of a sinusoidal one and with higher frecuencies, at least 400 Hz, that in practise behaviour "at sight" like if it was DC. But switched power supplies, like switched xenon rectifiers, are not as reliables as magnetic ballasts/high reactance rectifiers that last practically forever, though last generation ones are a lot more reliables. One economic solution is using these cheaper magnetic ballasts and projecting at 25 f.p.s. and there won´t be any flicker as it´s used at filming (though at filming you can do it at 24 f.p.s. with no flicker adjusting the variable shutter). I´ve done it with 16mm projectors (Eiki and Hortson) and with Bauers is very easy to do due to their electronic controlled DC motors. As for HTI 400W/24 or HTI 403W/24 lamps used on Bauer P8 T400 projectors due to their wonderful dichroic compact mirrors (with three different radiouses!), using the adequate condenser lenses you can fill the 35mm aperture (they are intended for a 16mm aperture) and get a light output similar to a 1.000 watts xenon bulb (some people that has installed this lamp on 35mm portable projectors say 1.600 watts...)
Of course you´d have to install a douser cause they need a short warm up (less than half a minute). This their greater inconvenient. Few years ago their short rated life was another one but now metal hallogen arc lamps last from 250 to 3.000! hours depending on types.

Alejandro.