[Kelvin1965S]

I had to redo my JVC HD350 calibration (with external VideoEQ Pro CMS/greyscale/gamma) due to a flicker on the normal lamp mode, which is cured by using high power. Before I started, I took a measurement with my previous normal lamp calibration settings applied, then did another run with the same settings having only changed the lamp setting.


I thought this might be useful to show just how much effect the lamp setting (and no doubt changing the lamp) makes to the picture. I don't know if it was a slight 'glitch' in the reading, but notice that the gamma is slightly different between these two runs. I've seen it written that the JVCs gamma drifts over time as the lamp ages, this seems to show a measureable difference in gamma just by changing the lamp power. The 20% extra red was what surprised me, I don't know if this is typical or whether this might be a side effect of the wandering arc causing my flicker? Note that the flicker wasn't occuring during the normal power run, it tends to start after being on for a few hours, but last night it had been on for 4 hours at least. However, I know it might come back at any time, so I've deceided just to stick with high power and a lower iris setting instead (maximum ON/OFF contrast in this configuration as well).


For information: The readings are taken from the projector with diffuser in place using an offset calibration taken from the screen. The pre readings are 'Normal' lamp and the post readings 'High' lamp power.

 

Low lamp pre high lamp post.pdf 142.1376953125k . file

 

[Hughman]

The extra red in high lamp mode is normal and the mode JVC uses to obtain spec's and calibrate the projectors. What doesn't appear normal in the charts is the amount of brightness obtained switching from low lamp to high, you appear to be achieving a 67% gain where one would typically expect to see around a 20% increase in lumens. Was the meter moved closer to the pj for the high lamp readings?

 

[Kelvin1965S]



Quote:
Originally Posted by Hughman /forum/post/18215576


The extra red in high lamp mode is normal and the mode JVC uses to obtain spec's and calibrate the projectors. What doesn't appear normal in the charts is the amount of brightness obtained switching from low lamp to high, you appear to be achieving a 67% gain where one would typically expect to see around a 20% increase in lumens. Was the meter moved closer to the pj for the high lamp readings?

Not sure what's going on there.

The meter was set up with the diffuser and placed facing the projector (after the initial offset calibration) and left in the same place for both runs). I'll try another pair of runs next time I have the sensor out (obviously I'll have to use the new calibration settings for this, but it will at least confirm the differences). I'm wondering if I changed my user setting from '1' to '2' which is identical except for the iris position, but I can't be sure now. Of course changing the iris may well also alter the results, so I will repeat and recheck that the iris remains the same for both runs. Then I'll do an iris change and remeasure the same lamp mode with different iris settings.


What is also strange is that according to Chromapure's readings I was getting a contrast of around 50,000:1 (though I guess this is more to do with my meter's inaccuracy for the '0' IRE reading).


Will post back repeated results later.