|Originally posted by guitarman
That was mighty nice of you setting up the format. I've been doing some things the wrong way. About CR check, which is the best way to aim each meter for best results? I've been using the Tri-chromat at the screen :(
Newbie's! ;) How far away from the projector lens do I want to have the Tri-chromat?
Same ? for the One-eye, how far away from the screen?
Another thing tricks for dark reading with the Tri-chromat, the Ony-eye has a neat black lens slide. I've beening laying black velvet over the Tri-chrome but feel light is still seeping in. What do you do?
I use a dedicated light meter to measure Black and White for on/off CR measurements. None of the mid-priced colorimeters are sensitive enough at Black. The margin of error is too great. I usually mount the light meter anywhere from 5' to 3' from the PJ's lens to reduce the margin of error to a negligible degree.
As for aiming a trichromat, I use a makeshift aiming device that is considerably faster than trying to aim the sensor via its readings. What I use varies with the physical construction of the sensor. For example, the original Colorfacts sensor (a modified Colorvision Spyder) has a protruding sensor eye. I found a PVC pipe fitting that snuggly fit over the housing of the eye and sticks out about an inch from the sensor. I wrapped a rubber band around the fitting and the body of the sensor to make sure it didn't fall off. When the fitting, and thus the eye of the sensor, is pointed directly at the PJ (display a 100 IRE screen to make it easy to see), it casts no shadow on the body of the sensor. When you move the sensor even slightly in one direction, it casts a shadow on that side of the body of the sensor. It works under the same principal as the sundial.
For the OpticOne sensor I use the cap from a can of Pam cooking spray. I stick it to the numerous tiny suction cups which surround the eye of the sensor and are intended to attach the sensor to a CRT monitor. Inside of the middle of the cap is a tube that is an inch in diameter and sticks out an inch from the base of the cap. I position the cap so that the tube is directly over the eye of the sensor. I use the shadow cast by the tube against the base of the cap to tell when the eye is pointed directly at the light source (the PJ).
Mounting a Trichromat closer the PJ will allow you to measure color accurately at a lower IRE level as compared to what it can measure accurately when positioned at the screen. For example, it might allow you to measure 20 IRE accurately when mounted closer to the PJ vs only being able to measure 30 IRE when mounted at the screen. If you get too close to the PJ, you can oversaturate the sensor at 100 IRE. You will know this because the reading will be wildly inaccurate. This distance varies with the sensor (they vary in sensitivity and dynamic range) and with the brightness of the PJ. For example, my OpticOne sensor has to be mounted at least 64" from the lens of a SP7200 (with 500 hours on the PJ Bulb) to avoid over saturation at 100 IRE. With a Marantz S3 in its dimmest mode, it could probably be as close as 3' from the lens of the PJ.
I have not found it necessary to shield the trichomats from room reflections because the light from the lens is so much brighter than the room reflections that they overpower them. However, if an LED is within its field of vision, it will skew the sensors reading near Black, especially with the light meter. I have experimented with creating a black velvet tunnel between the PJ and the light meter (which is much more sensitive than the trichromat sensor) but saw an insignificant difference in the readings.
There are logistical problems with trying to mount sensors near the PJ in that furniture is usually in the way. A tripod will not get the sensor high enough for a ceiling mounted PJ. When I want to do this, I bungee cord my tripod to a step ladder to get it up into the light stream.