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Xenon short-arc lamp: Difference between revisions
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Whenever a new xenon lamp is installed it must be properly aligned on the X, Y and Z axis (horizontal, vertical, axial) to have even illumination and achieve the proper luminance on screen. Poor lamp alignment can result in hot spots of light on screen, damage the reflector, lens, and even the print. A lamp alignment should be performed when a new lamp is installed and periodically thereafter because the position may drift over time. | Whenever a new xenon lamp is installed it must be properly aligned on the X, Y and Z axis (horizontal, vertical, axial) to have even illumination and achieve the proper luminance on screen. Poor lamp alignment can result in hot spots of light on screen, damage the reflector, lens, and even the print. A lamp alignment should be performed when a new lamp is installed and periodically thereafter because the position may drift over time. | ||
Lamp alignment should be done whenever a new lamp is installed | Lamp alignment should be done whenever a new lamp is installed. Lamp alignment should also be checked if you see hot spots or shadows on screen or if you discover embossing or burns on prints that you have run. If you are switching between different [[Film gauges]] on the same projector, the position of the reflector should be adjusted to achieve the correct [[working distance]] between the focal point of the reflector and the aperture. Most dual format lamphouses have a toggle switch to make this adjustment. | ||
Most lamphouses have a mechanical adjustment to shift the position of the cathode end, while the anode end is supported by a post or yoke with an adjustable height. The height of the anode can usually be set during the initial installation, with only the cathode end being adjusted at every lamp change. If you center the cathode end, it will be apparent if the anode position is incorrect because the lamp will not be straight. | Most lamphouses have a mechanical adjustment to shift the position of the cathode end, while the anode end is supported by a post or yoke with an adjustable height. The height of the anode can usually be set during the initial installation, with only the cathode end being adjusted at every lamp change. If you center the cathode end, it will be apparent if the anode position is incorrect because the lamp will not be straight. | ||
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1. Turn on exhaust, make sure lamphouse dowser is closed. | 1. Turn on exhaust, make sure lamphouse dowser is closed. | ||
Always have lamphouse dowser closed before striking a lamp | Always have lamphouse dowser closed before striking a lamp. Striking a lamp with the motor off and the lamphouse dowser open can melt the [[shutters|shutter]] blades and changeover dowser, and can crack the lens. | ||
2. Remove lens ([[Kinoton]] users should remove | 2. Remove lens ([[Kinoton]] users should remove the skate so that it isn't damaged by the heat). Turn on lamp. Start motor and open dowser. | ||
3. Make the axial adjustment | 3. Make the axial adjustment (the “focus” on the Z axis) til you see a circle with a little bit of plasma around the edges of the anode shadow (people call this “the eye”). | ||
4. Make your horizontal and vertical adjustments until you get as close to a symmetrical circle as possible. | 4. Make your horizontal and vertical adjustments until you get as close to a symmetrical circle as possible. | ||
5. Re-adjust the axial to bring the plasma back | 5. Re-adjust the axial alignment to bring the plasma back into focus, until you have a tight symmetrical circle free of light (plasma) fluttering around the anode shadow. | ||
6. Put in a lens ([[Aspect ratios| | 6. Put in a lens ([[Aspect ratios|CinemaScope]] is usually best as you want the largest aperture). After you put the lens back in look for even illumination across the screen. With the lens in, the shadows will be gone and there will be a hotspot in the center of the screen. Focus the lamp (making fine X and Y axis adjustments as necessary) until no shadows are visible at the corners and the illumination is even across the screen. You want it bright, flat and centered with no hot spots! Changeover from projector 1 to projector 2, you want them to look as similar as possible. | ||
7. You may want to fine-tune the | 7. You may want to fine-tune the lamp focus with the lens in place until you have even illumination, then take the lens out again to check the symmetry of the anode shadow. | ||
'''WARNING:''' The heat from the lamp can crack the glass of the lens when there’s no film in the gate, so the dowser can only be opened for brief periods during the alignment. For a 2kW lamp, the dowser should be opened for no more than 30 seconds at a time, with breaks between for the lens to cool down. For large lamps, use quick bursts of light and a long cooldown period. Consult your service technician before making these adjustments! | '''WARNING:''' The heat from the lamp can crack the glass of the lens when there’s no film in the gate, so the dowser can only be opened for brief periods during the alignment. For a 2kW lamp, the dowser should be opened for no more than 30 seconds at a time, with breaks between for the lens to cool down. For large lamps, use quick bursts of light and a long cooldown period. Consult your service technician before making these adjustments! | ||
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===Measuring Luminance=== | ===Measuring Luminance=== | ||
The [[Society of Motion Picture and Television Engineers|SMPTE]] specification is 16fL ([https://en.wikipedia.org/wiki/Foot-lambert foot lamberts]) with uniform illumination across the projected area without film in the projector (open gate). Because | The [[Society of Motion Picture and Television Engineers|SMPTE]] specification is 16fL ([https://en.wikipedia.org/wiki/Foot-lambert foot lamberts]) with uniform illumination across the projected area without film in the projector (open gate). Because the 1.85:1 "Flat" [[aspect ratio]] uses the smallest aperture it is the least light efficient, while 1.33:1 silent or 2.39:1 CinemaScope apertures are the most light efficient. You can split the difference by using 15fL for [[Aspect ratios|1.85:1]] and 17fL for [[Aspect ratios|Cinemascope]] to achieve a balance within SMPTE specifications. | ||
If you’re checking luminance through the port glass with your meter subtract 1~2fL. It’s always best to take your final readings in the auditorium itself. | In most circumstances a fixed-height screen will evenly balance the light output between the smallest aperture (1.85:1) and the largest aperture (typically 2.39:1) because the greater light output from the CinemaScope frame is used to illuminate a larger screen area. However, this is complicated by movable vertical [[masking]]. When the height of the screen can be increased for narrower formats, the light requirements can vary dramatically. Stopdown rings can also be used to reduce the light output of formats with a larger aperture (1.33 or 1.37) to achieve the necessary balance of light output between aspect ratios. | ||
If you’re checking luminance through the port glass with your meter, subtract 1~2fL from the reading. It’s always best to take your final readings in the auditorium itself. | |||
===Potential Issues=== | ===Potential Issues=== | ||
* If you can’t evenly distribute the plasma with lamp alignment (you’ll notice it will appear asymmetrical even as you adjust the focus), the arc stabilization magnet may need to be adjusted by a trained technician. Excessive flicker may result if the plasma isn’t evenly distributed. | * If you can’t evenly distribute the plasma with lamp alignment (you’ll notice it will appear asymmetrical even as you adjust the focus), the arc stabilization magnet may need to be adjusted by a trained technician. Excessive flicker may result if the plasma isn’t evenly distributed. | ||
* If dark spots appear in the area within the circle of light | * If dark spots appear in the area within the circle of light with the lens removed, the reflector should be inspected for pitting, explosion damage, or any other damage to the reflective coating. | ||
* Damaged | * Damaged lamp | ||
* Cannot focus | * Cannot focus lamp because of physical lamphouse alignment in relation to projector (the "working distance" between the focal point of the reflector and the aperture is incorrect) | ||
===Damage=== | ===Damage=== | ||
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==Lamp Safety== | ==Lamp Safety== | ||
[[File:Safety gear.jpg|right|thumb|200px|Example of safety gear worn during lamp | [[File:Safety gear.jpg|right|thumb|200px|Example of safety gear worn during a lamp change]] | ||
An exploding lamp will expel shrapnel in all directions, so a face shield and full-body protective clothing must be worn when handling xenon lamps. Some lamp manufacturers sell safety gear, but protective clothing designed for welding is more readily available and usually cheaper. | An exploding lamp will expel shrapnel in all directions, so a face shield and full-body protective clothing must be worn when handling xenon lamps. Some lamp manufacturers sell safety gear, but protective clothing designed for welding is more readily available and usually cheaper. | ||
Each theater should stock safety gear in multiple sizes. This is especially important for gloves, because ill-fitting gloves will limit dexterity and make handling the lamps more dangerous. | Each theater should stock safety gear in multiple sizes. This is especially important for gloves, because ill-fitting gloves will limit dexterity and make handling the lamps more dangerous. | ||
Lamp | Lamp changes should only be done by a service technician or someone who has been properly trained by a service technician. | ||
Safety gear should include: | Safety gear should include: | ||