11HT First Impressions, and a Question

Thanks Steve, I already have a copy of your SMART spreadsheet, but am still waiting for the Detector and filter to arrive. I ordered a CC30R, as I did not want to overcorrect at all (I want it as bright as it can possibly be)

Have you found out any more about that annoying 11HT "feature" yet?

Or how to get around it?


Can I expect the same sort of improvement again with the filter, to what I saw by increasing the gains by eye?


Also why do you reccomend not to push the red gain up to 255 for the first run on an 11HT?


Regards

Brett D

I have used SMART to determine the light output at IRE 100 and the gamma tracking with two different color temperature. One used my red gain at the factory low’s value of 193 and contrast at 77. The second one had the red gain at 250 and the contrast at 67. I used the detector in both cases to assure that my contrast was right on the edge where a higher value would not produce more light, but a lower value would.


In both runs the two color temperature and appropriate contrast settings produced exactly the same light output at IRE 100 (and 0) and the same gamma tracking. This makes sense and the light output for a given color should really be the product of the gain for the color and the contrast value. You can get the same light output with a wide combination of numbers, but when there is no more red to be had,, there is no more red. Boosting the gain to 255 does not produce any more light at IRE 100 that boosting the contrast an equivalent amount.


The problem with the 255 tweak is that unless you lower the contrast sufficiently to avoid blowing out the red, you do get more light out at the lower IRE levels, and at first it looks good. In reality however, you are experiencing significant shifts in color balance at the high IRE levels because red simply runs out of gas, and this can lead to funny colors and loss of details in highlights, etc. For accurate reproduction of video, you really should operate the projector in the range where the gamma tracking and color balance is correct and that there is more light (for all colors) at IRE 100 than at IRE 90.


With the 11HT and without the CC filter, this means keeping the green and blue gains well below red, and hence the contrast ratio is sub-optimum. With the CC filter in place, you can drive all colors pretty much to the same extent and they all run out of gas together. This is a much better situation in terms of color shifts, though in this case as well, you should operate in a contrast/gain range where gamma tracking is still accurate.


Bill Cushman started the 255 thing with the 10HT, and I (and Don, etc) certainly kept it going. When we both switched to 11HTs, he mentioned that the 255 thing really didn’t make sense and so I changed my strategy with SMART for the11HT to keep the red gain at the factory low value, and simply raise the others.


Another user recently questioned this, and so I carefully compared the two runs described above, and again, could find no advantage (or disadvantage) to pushing things to 255 or so. Once you are set up with the detector, you can make your own measurements and decide for yourself! I’ll be very interested.


So where does this leave the 255 thing with the 10HT? Good question. I haven’t bothered to set mine up again, but I probably will before I sell it (soon). In the meantime, anyone else with a 10HT doing SMART can do the same tests described above. The key, of course is to make sure that the contrast is set correctly for each run, and I now have a very convenient detector based way of measuring this on my web-site and in the manual.


Good luck.


Steve