Xenon short-arc lamp: Difference between revisions

Xenon short-arc lamp (view source)

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→‎Lamp Alignment

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 ==Lamp Alignment==
-A lamp must be aligned in order to properly illuminate the screen. A lamp alignment should be performed when a new lamp is installed and periodically thereafter because the position may drift over time.
+Whenever you put in a new xenon lamp 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.
 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.
-The lamp alignment should be performed using the largest aperture available (usually CinemaScope) in order to best assess light drop off at the corners. The lamp must be aligned with the projector running (the shutter must be rotating) and the aperture plate inserted, but without film.
+During alignment you will see the following on screen: The shadow of the anode assembly at the end of the lamp is the dark circle, immediately ringed by visible plasma (the electron arc). Surrounding it is the circle of light collected by the reflector, and reflected upon the screen. This area comprises most of what we see, and should appear bright white and essentially even in luminance upon completion of the alignment.
-First, make a coarse adjustment without the lens in place. With the projector running, strike the lamp and open the dowser. The hole from the back of the reflector will appear as a dark circle on the screen, and the shadow from the anode end of the lamp will be a darker circle in the center. The anode lead will also cast a shadow, which will be visible as a curved line running out from the circle.
+===Lamp Alignment Steps===
-Adjust the focus (Z axis) until the shadows are sharp, then use the horizontal and vertical adjustments to center the shadow of the anode within the larger circle. The shadow should be as round as possible, and the concentric rings that appear around the circle should be symmetrical. The illumination should be even on all sides of the circle.
+. Turn on exhaust, make sure lamphouse dowser is closed.
+Always have lamphouse dowser closed before striking a lamp -- striking a lamp when the motor is off and the dowser open can result in melted shutter blades, changeover plates, melted film, or cracked lenses.
-After making this coarse adjustment, close the dowser and insert the CinemaScope lens.
+. Remove lens (Kinoton users should remove gate runners so aren’t damaged by the heat). Turn on lamp. Start motor and open dowser.
+. Make the axial adjustment, (or the “focus”) till you see a circle with a little bit of plasma around the edges of the anode shadow (people call this “the eye”).
+. Make your horizontal and vertical adjustments until you get as close to a symmetrical circle as possible.
+. Re-adjust the axial to bring the plasma back in, until you have a tight symmetrical circle free of light (plasma) fluttering around the anode shadow.
+. Put in a lens (cinemascope is best as you want full 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.
+. You may want to fine-tune the bulb 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!
-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.
+. Finally, take a light reading with your luminance meter.
 ===Measuring Luminance===