Film-Tech Forum ARCHIVE: CX20H lamp type

This is topic CX20H lamp type in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Thomas King (Member # 2745) on 02-28-2006, 04:20 AM:

Hi,

I have a Vic5/CX20H lamphouse/silver(non dichromatic) reflector/2 blade shutter/ISCO gold lenses/20m throw/reflective (non perferated) screen.

Can someone please tell me which lamp I should be using? In the past I see that people have had 2kw, 1.6kw and 1kw lamps fitted.

As far as I can work out, a 1.6kw lamp should be right for me, but I'd like to check the opinion of people who actually know about this sort of thing.

Many thanks.

Posted by Pete Naples (Member # 761) on 02-28-2006, 05:27 AM:

We'd need to know the picture sizes for the advice to be of any value. Throw is largely irrelevant.

[ 02-28-2006, 06:57 AM: Message edited by: Pete Naples ]

Posted by Thomas King (Member # 2745) on 03-02-2006, 03:41 AM:

Sorry, my bad; I knew I'd left out something important. The visible screen area for anamorphic is 10mx4m (or near as).

[ 03-02-2006, 06:57 AM: Message edited by: Thomas King ]

Posted by Louis Bornwasser (Member # 3063) on 03-02-2006, 08:30 AM:

Use 2k bulb. Better warranty and more light. Prob. longer life too, since you are not running at 100%. My experience (osram) is that the 2 k is their very best bulb while the 1.6k is not as good. Louis

Posted by Thomas King (Member # 2745) on 03-02-2006, 09:21 AM:

I was under the impression that a 2kw bulb required a dichromatic reflector, otherwise the heat focused on the film would cause meltage.

Posted by Gordon McLeod (Member # 33) on 03-02-2006, 10:03 AM:

On the horizontal cinemecanica lamphouses you basically have two choices
hot mirror and heat filters or a cold mirror (dichroic) and no heat filters and with 3K and larger both heat filters and dichrocic reflector

Posted by Thomas King (Member # 2745) on 03-02-2006, 10:45 AM:

I don't have heat filters, so I'm guessing that 1.6kw will do the trick.

While I'm here; how often should a xenon of this capacity be rotated? I'm guessing that it's a case of the more frequently the better.

Posted by John Pytlak (Member # 331) on 03-02-2006, 12:26 PM:

The need for a heat filter or dichroic mirror is dictated by the amount of radiant energy going through the film frame. Whether you use a 1600 watt or 2000 watt lamp makes no difference if you change the current and/or lamp focus to maintain equivalent light output. I usually prefer to use a larger lamp, and defocus to get better uniformity of illumination, rather than have a smaller lamp maxed out and hot-spotted to get 16 footlamberts in the center of the screen.

Posted by Louis Bornwasser (Member # 3063) on 03-02-2006, 12:54 PM:

On Osram, there is no longer any requirement to rotate; you may do so at your option. Louis

Posted by Fabrice Dubourg (Member # 1635) on 03-02-2006, 04:32 PM:

use a 2k lamp but there is a problem with osram on these lamphouse.
the wire on the lamp is to near of the miror with an osram and when striking the lamp an arc can go from the wire on the miror and the ignition is then hard!!
just compare the diameter of the lam near the bulb between an osram and an ushio.

Posted by Jerry Axelsson (Member # 3175) on 03-04-2006, 07:00 PM:

Thomas, we have Vic 5:s with the lamphouse you mention.

I recommend that you use 1600w bulbs for them. The light output may not be 100% what one would need in all situations, but 2kW bulbs have a tendency to get overheated and last few hours when we have used them in these lamphouses.(read 1000-1500 hrs for 2kW bulbs) Perhaps this is due to the deep mirror?

We have powerful ventilation for our lamphouse, but the problem remains.

Posted by Demetris Thoupis (Member # 833) on 03-05-2006, 01:49 PM:

Preferably use 2k lamp. I've found USHIO to be more reliable than OSRAM lamps in this lamphouse. Even at 1600W the light output is great as long as the lamphouse is correctly allinged. Is the lamphouse on the proper mounting of the projector or is the lamphouse retrofitted in an older type pedestal? You should be sure that the allingment is correct otherwise use any lamp and you won't get the desired result.
D

Posted by Thomas King (Member # 2745) on 03-06-2006, 05:01 AM:

Thanks for all your responses; I'm going to order a 1600w because all indications lead to a 2kw at full power being too hot (it's a very dinky lamphouse). I'll take light readings and let you know the results.

The way I align the mirror is to take it all the way back, and then center the bright spot, and then take it forward until the bright spot fills the screen. Is this good, bad or ugly?

Posted by Pete Naples (Member # 761) on 03-06-2006, 06:40 AM:

Is this the tiny little thing that you have to slide the mirror back to change the lamp? If so those are bloody dangerous IMHO, how the hell can you get the jacket over the bulb to screw/unscrew it? You can't! You have to screw the lamp in and out with your fingers, no chance of wearing gloves unless you've got doll size hands 'cos you won't get your paws in there.

They do run ferociously hot, anyone who's seen the latest 'Cinema Technology' magazine will see a pair of them behind DP75's on the front cover. We had to go to water cooling on the DP75s with a 1600w lamp, even with healthy forced extraction.

Posted by Thomas King (Member # 2745) on 03-06-2006, 08:02 AM:

You do indeed have to slide the mirror back to get the bulb in, and even then it's remarkably difficult. The hole in the mirror will only just allow the crossbar on the lamp terminal through if you tilt it just right, you have to take the lamp out of its sheath beforehand (I protected it by wrapping a lens wipe around it) and wearing gauntlets make you feel like an elephant trying to do brain surgery, not to mention that the anode cable is so long you have to be really careful that it doesn't get near to the douser or frame, otherwise your ignition spark will just arc straight to ground.