Alan I can give one piece of advise. I local photograhy supply shop for the filter. I paid $15.00 after tax for a Hoya MC. Seems it's going for $30.00 shipped over the internet. IF you can find it. I thought I heard mention that the 5500's lamp is high in red? Please someone give me us the scoop.
I have a Hoya filter. Im trying to reduce the blue push at the low end of the grey scale. Ive seen the mention of numorous filters for this but no mention where to buy them. Hopefully someone with experience using these filters will chime in.
I bought a Kodak filter viewing kit in a local photo shop (Georgeâ€™s Camera) for $24.95 (+Tax). It contains several color correction filters; cc10, cc20, cc40 of Red, Green, Blue, Cyan, Magenta, Yellow. These filters are low quality versions of the high quality Kodak CC gelatin filters, but perfect for experimenting.
The projectors differ in the amount of "light leakage" (blue and red), but you will most likely need a denser (higher CC number) Yellow (to reduce blue) then Cyan (to reduce red). Bear in mind that the use of filters cause light loss and color shifts that need to be compensated for. Not sure yet if filters are the way to go...
The bulb in the Hitachi is a UHB bulb (not UHP). I have tried to find a spectrum for it w/o success. This is something you may want to ask Hitachi about tomorrow. (Also please do not forget to ask them about policy of fixing/upgrading current projectors)
In any case I have done some measurements, and I easily saturate red on my projector, so I do not think that there is any excess red in this bulb.
For all tweaks, I think that it is absolutely necessary to measure the light output at Red, Green and Blue to determine the proper light vs. IRE response (the "gamma curve").
The cheapest way to do this is to use a Radio Shack photocell ($3) with the AVIA disk ($40) and supplied RGB filters. To do it yourself, needs some optical know-how, some of it which you can gain from reading Steveâ€™s web site:
I have had the privilege of working with rbrande on this (he's very sharp!) so I thought I'd add my 2 cents worth on the filter issue, based on what I have learned from his measurements using SMART. SMART can certainly see the problem, but correcting it is another matter entirely.
The contrast ratio for a given color is limited by the leakage light with no input, and the maximum output of the fully driven panel or color wheel or whatever. The maximum contrast ratio possible WITH proper color balance will be the lowest contrast ratio of the three colors. Filters, CC or ND or FLD or whatever allow you to move the absolute intensity of the various colors down, but can't actually change the contrast ratio.
For many projectors where the bulb is short on a given color, e.g. red, contrast ratio can be improved by combining filter with increased drive levels on the panels as has been well described in other threads. For these same projectors, the leakage mechanism or pathway is similar for the three colors, and the leakage light will resembles the spectrum of the bulb. Hence you can add a CC filter to correct for a bulb that is short on red and at the same time, correct the color temperature of the leakage light. Im theory, (and practice) it's a win win, the contrast ratio goes up, the black level down and color balance is maintained or improved at all IRE levels.
The situation with the Hitachi seem a bit different. In this case the leakage light for blue, and perhaps red as well, are much higher than they should be, relative to green. The leakage light does not resemble the spectrum of the bulb. While the measured contrast ratio for green is very good, the contrast ratios for red and blue are much less, and to put it bluntly, poor.
So what to do. One can restore the color balance at IRE 0 - 20 by upping the green intensity at those levels, but the contrast ratio and black level goes to pot in the process. One can use filters to move the intensity of the various colors down, but the contrast ratio will probably not be improved.
So it seems that one most choose between blue or purple blacks or take the hit on contrast ratio and black levels as described above.
I will add that there is probably some middle ground here in that one can tolerate some lack of color balance at low IRE levels, but as the eye is very sensitive to blue in dim lights, blue is probably not the best color with which to have leakage.
My take on all of this. Of course I could be entirely wrong:
The other night I removed all of the blue in both the service and user menus, but still noticed a small blue tint in the red. It takes only a tiny bit of blue to bespoil a pure red. (Ever been behind someone with a little blue jewel lens in a red taillight and see how it tints the color violet?) It would then appear that there is a blue "leakage" due to bulb color, incomplete blue light blockage, or ???
Lets say that the blue can be scaled from 1-200. Now lets say that of the 200, we only really need 100 and the rest is surplus. (Who turns up blue all the way???) Finally, lets say that the blue leakage amounts to 10.
Therefore, the blue contrast is 100:10 or a ratio of 10:1.
Now let's say that we add an orange filter (complementary to blue) and let's say that the filter has a 50% reduction efficiency for blue. This reduction is applicable to ALL blue passing through the system. Thus, our leakage is now reduced to 5, (i.e., 10 x 50%), but max blue is also reduced to 50 (i.e., 100 x 50%). So, 50:5 is still a ratio of 10:1.
But we have a surplus of blue available for use, so lets double the blue setting to 200. The orange filter now reduces this value to 100 (i.e., 200 x 50%) while reducing the leakage to 5 or 100:5. Therefore, the contrast ratio is now 100:5 or 20:1.
Can it really be this simple? Where is the flaw in my logic?
Your reasoning is correct, and I actually tried it. Unfortunately, the Hitachi does not have excess blue (or red).
If you turn your contrast up to optimum (e.g. not saturating the white, IRE100 is still significantly more intense than IRE90 so that they both lie on the "gamma curve") you have the best possible contrast ratio (e.g. 500:1).
However, if you try to increase blue at this point, it will saturate. For example, increasing blue from 100 to 200 (to compensate for the 50% filter loss) causes the blue intensity at IRE 80, 90 and 100 to be similar.
In other words, increasing blue to compensate for the filter will cause saturation and color shifts (a lot of yellow at IRE>80).
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