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Topic: 250W lamp in an ST-1200... can I do this?

Jan Bister
Darth 8mm

Posts: 2629
From: Ohio, USA
Registered: Jan 2005

posted August 16, 2006 11:20 PM

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The Doctor is asking for assistance...

Thinking about beefing up the lamp in my Elmo ST-1200HD, replacing it with a 250W ELC bulb. This would be powered by an external transformer (probably from a 16mm projector), and I would most certainly rig up a large fan of some sort (mounted on the front cover over the lamphouse) to provide extra cooling.

Question is... would the film gate itself be able to take the extra heat? How much light will I lose due to the fact that 250W ELC bulbs are made to focus on a 16mm gate, not a super-8 one?

Will the increase in light output be worth it in the end?

--------------------
Call me Phoenix. *dusts off the ashes*

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Kevin Faulkner
Film God

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From: Essex UK
Registered: Jun 2003

posted August 17, 2006 08:05 AM

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In theory yes it's possible to do but yes there will be some trade off because (as you say) the lamp is designed to cover the 16mm gate. Because of this you will have to also make sure that the rear of the gate is cooled well. The spot of light will be concentrated over a larger area of the gate so it will get hotter.

The 8mm 15V/150W lamp as supplied in the ST1200 is a very efficient beast especially the Osram HLX version so dont know if I would go to all that bother.

You do get a nicer less green looking light by simply removing the built in heat glass which I think is there mainly for projecting at the slower 18fps. As the fan is on the end of the main motor you get less cooling at 18fps. If you use the machine mainly for 24fps projection then take the filter out.

Kev

--------------------
GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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Jan Bister
Darth 8mm

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From: Ohio, USA
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posted August 17, 2006 01:22 PM

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The filter is long gone already. [Wink]

[Wink]

My reason for asking was that I encountered a rather dim image during my first scope projection. It's possible that ambient light fooled me (as I only did a test run and the room was not 100% darkened) - I also know that Derann's new prints are fairly dense and generally a bit darker than your typical used, decades-old film - it's also conceivable that my scope lens introduces too much light loss. Not sure about that, would have to check again... It's a Kalart Victorscope, probably a fairly average scope lens (but I got it for very cheap), so I may upgrade to a better one later on. [Smile]

[Smile]

Anyway, my real interest was in the trade-off between the gain in light output and the loss due to 16mm-gate focusing, and I have my answer now. Thanks [Smile]

[Smile]

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Call me Phoenix. *dusts off the ashes*

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Craig Hamilton
Jedi Master Film Handler

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From: Luton
Registered: Sep 2004

posted August 17, 2006 01:52 PM

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Jan

Why not go all the way & become the owner of the only Elmo ST-1200 HDI in the world [Wink]

[Wink]

Craig

--------------------
I dream of becoming a dealer!!!!!!
Is Perry's Movies for Sale.

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Jan Bister
Darth 8mm

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From: Ohio, USA
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posted August 17, 2006 01:58 PM

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Y'know, the thought HAD occurred to me [Wink]

[Wink]

Maybe I ought to pick up an Eiki Xenon and strip 'er down... [Big Grin]

[Big Grin]

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Call me Phoenix. *dusts off the ashes*

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Jean-Marc Toussaint
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From: France
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posted August 18, 2006 02:51 AM

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Ah... Looking forward to witnessing a new experiment. Yummy.
Jan, yes, scope needs a lot of light.
Now, silly question, wouldn't trying to fit a 24v-200w from a GS 1200 be easier? ESCs are - after all - made for the super 8 gate and if you add an F1:0 or and F1:2 lens (depending on your projection throw), you will really gain in brightness.

--------------------
The Grindcave Cinema Website

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Kevin Faulkner
Film God

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From: Essex UK
Registered: Jun 2003

posted August 18, 2006 03:20 AM

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But ESC lamps are no longer available, only the EJL std version and thats designed for the 16mm gate as well. [Frown]

[Frown]

I think an HTI conversion is the way to go but with an extra fan on the side.

Kev

--------------------
GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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Jean-Marc Toussaint
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posted August 18, 2006 03:46 AM

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Ah, yes, I stand corrected. So, before going the HTI way, isn't it worth trying to install an EJL first?

--------------------
The Grindcave Cinema Website

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Jan Bister
Darth 8mm

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From: Ohio, USA
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posted August 18, 2006 10:47 PM

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I don't even know how HTI lamps work - still wrapping my head around the whole Xenon thing - have some trouble understanding the whole ballast business and all that. Incandescent/halogen bulbs are so much simpler [Eek!]

[Eek!]

So... to bring up scope lenses again, is there a big difference between the best and worst scope lenses in terms of light loss? Where does my Kalart Victorscope fall? What should I be looking to replace it with, if I decide to do so?

And Jean-Marc... why do I keep thinking of that old Colecovision video game system everytime I see your sig... [Big Grin]

[Big Grin]

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Call me Phoenix. *dusts off the ashes*

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David Kilderry
Jedi Master Film Handler

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From: Melbourne, Victoria, Australia
Registered: Feb 2006

posted August 18, 2006 11:46 PM

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Jan, a scope lens is designed to double the width of the image projected through it whilst keeping the height the same. By doing this your light on Super 8 and 16mm scope films (2.66:1) will be only half what it was with the standard 1.33:1 aspect ratio.

Remember it is not the throw that costs on screen light, it is the image size.

Having said that, some scope lenses are more eficient than others, but the wider image is what costs the most light.

In 35mm projection it is a little different, as the scope frame on the 35mm film is much larger (by around 40%) than the regular 1.85:1 widescreen flat image.

David

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Graham Ritchie
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posted August 19, 2006 02:15 AM

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Hi Jan
Before using the 35mm for scope I used a Proscar 16mm anamorphic which was supposed to be quite good, even with this lens the drop in light was noticeable, the reason I mention this is that your lens might be fine. I was thinking is it worth contacting the Widescreen centre, they certainly have been in the business for quite a while and might be able to help.
Jean Marc mentioned using the EJL 24v/200watt which is a good idea, you could even try a ELC/5H Philips 24/250watt rated for 500hrs use with extra cooling, out here you can buy stand alone 24volt power supply for this purpose, well Jan hope this is of some help.
Graham.

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Jean-Marc Toussaint
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posted August 19, 2006 02:57 AM

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Jan, if you do a search on the web (sorry, I lost the bookmark) you'll find a chart comparing all available scope lens, pros and cons, loss of light, size, and so on and so forth.

And you're spot on, if you visit my store (no purchase necessary [Big Grin]

[Big Grin]

) and have a look at the logo, it will probably bring back some memories... [Wink]

[Wink]

--------------------
The Grindcave Cinema Website

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Kevin Faulkner
Film God

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From: Essex UK
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posted August 19, 2006 06:09 AM

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Jan, Yes the subject of Xenon/HTI etc is quite a complex subject but I like to think back to the days of early Carbon Arc projectors and how they worked. This then gives you a good idea of how these more modern lamps work.

The Crabon Arc was powered by monster power supplies and you got them to "Strike" by bringing the Carbon Rod tips together. Once the spark jumped between the tips you drew the tips apart again to maintain a bright even spark. As the spark dimmed down due to the carbon rods burning away you simply racked the carbon rods together to bring the brightness back. If this wasnt constantly checked it was possible for the spark to stop and the process would have to be started again to get the light back.
As you can see this was a very cumbersome process along with being smelly, dirty and dangerous and of course a fire hazzard.

With the Xenon and HTI lamps you can think of the Carbon Rods (in this case metal rods) enclosed in a glass tube with the tips at a predefined set distance. The enclosed glass tube is filled with an inert gas such as Xenon. The gas used determines the colour temperature of the light.
So now we have two rods which cant be bought together to get a spark to jump between them so what do we do? well we supply a very high voltage pulsed (AC) supply to get a spark to jump accross the gap and then throttle the supply back whith enough voltage/current to maintain the spark.
Due to the rods being enclosed in an inert gas they dont burn down at the rate the old carbon rods did (being in air) but they will deteriorate with use and eventually become difficult to strike or going out completely when in use. This is generally when they have had several hundred hours use. Generally the Xenon lamps last longer than the HTI versions but the voltages required for HTI versions are lower. I think that last statement is correct?

The power supplies are quite complex for these lamps and run at fairly high frequency (AC). If they are not designed well then you can get all sorts of problems. They use the "Switch Mode" Oscilator principal with EHT transformers just like the output stage in your tv set. Very high voltage and frequency is used to strike the lamp and then throttled back to a fairly low voltage, enough to keep the spark running.

You can think of a very high voltage supply to Ignite the lamp and then putting a ballast resistor in series with the lamp to reduce the voltage which is where the term Ballast came from. In early oscilating supplies I think its this principal which was used, hence the term Ballast Supply.

Some supplies are quite complex, sensing the current drawn, which enables them to determine if the lamp needs to be in Strike or Normal mode. This enables them not only to control the startup of the lamp but also to auto strike if the lamp stops running.

The lamps themselves are really quite straight forward but dont take too kindly to being moved or banged etc when running as they can explode and Oh boy do they explode. They are running at extremely high temperatures so good cooling is a must. When they are first struck you can often see some slight flickering (swirling) of the light untill they reach the optimum running temp which takes only a few mins and they also get brighter during this time. UV output is fairly high so you shouldnt look at the light directly for prolonged periods, mind you if you try looking directly at the GS Xenons lamp you will find it too bright to look at.
A dichroic filter is normally included in the light path to keep the harmfull UV and probably infra red off the film.

A real science but great fun and a superb white light which you will never get from a std tungstan lamp. Its a light which really makes colour jump off the screeen.

Its worth doing a google on HTI (metal halide lamps) and xenon lamps as that will bring up loads of interesting things to read.

Hope that quick overview helps and that I havent got it too wrong as I'm no lamp expert really.

Kev.

--------------------
GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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Paul Adsett
Film God

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From: USA
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posted August 19, 2006 09:27 AM

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Great overview Kev. Talking of exploding lamps, I thought this discussion on the UHP lamps, used in video projectors , might be interesting.
http://www.ercservice.com/lamps/philips/PhilipsUHPLamps.html

Looks like some of us have a bomb in our house! [Big Grin]

[Big Grin]

--------------------
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Jan Bister
Darth 8mm

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From: Ohio, USA
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posted August 19, 2006 05:41 PM

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Kevin,

that was wonderful. Thanks, this finally puts the puzzle pieces into place for me. [Smile]

[Smile]

Thanks to Paul for the link as well - I was actually wondering about the possibility of using video projector lamps for film [Smile]

[Smile]

David: you're right about the image size doubling of course and I was aware of that, but in my case I actually like to project "flat" images with greater vertical size than scope images - I have a pull-down screen that's 8ft. wide, so my scope films fill its entire width which puts the height at about 3.5ft. for an image area of about 28 sq.ft. ... whereas for flat films I increase the image height to roughly 4.5ft which gives me a width of 6ft. and a total area of 27 sq.ft. - almost identical! I know it is "standard procedure" to project flat and scope at the same vertical size but if I did that with my setup, flat projection would simply end up too small for my personal taste and lose its impact.
(I wonder if I'm the only one doing it this way?)

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Call me Phoenix. *dusts off the ashes*

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