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For years I have been extolling the virtues of optics cleaning of CRT RPTVs. And CRT ceiling projectors.

Now I see my focus has been way too narrow. Have you seen the look of 5 year old DLPs these days? It's classically bleary, just like the look of 5 year old CRT RPTVs. And even worse for 10 year old versions of both.

CRT has it worse because CRTs use 30,000 volts to produce their images. I didn't think DLPs would have the same problems because they only use a fraction of that in terms of HV, maybe a third of that, maybe a quarter. Unfortunately it turns out that that's enough to cause the same kind of build-up of impediments to a clear picture that CRTs suffer from as the sets age. After 5 years both - and any other projection medium, including D-ILA, LCOS, LCD and many front projection systems - will have a substantial amount of dust build-up on the optics in there as the sets age.

To exacerbate the situation, many DLPs use a second mirror to keep the thickness of the box to roughly half what it has always been for CRT. Wives love flat panels because they take up so much less space then the old boxy types like CRT, so DLP consciously designed their sets to be much less thick. This makes the box thinner, granted, but using a second mirror in there inserts that much more surface to get dirty, and since that mirror is just a fraction of the size of the main mirror but much closer to the lens, it gets far dirtier than the main mirror.

Result is a mirror that gets so dirty that I don't even have to draw a happy face in it to really show its owner what's happening in there. All I have to do is touch it - one small dit of touch from the back of one of my finger knuckles - and the black spot that results stands out like a sore thumb against the blanketing of dust that surrounds it when being illuminated by the strong projection lamp.

When that set of optics in there that gets dirty - for CRT with 28 surfaces it's either 4 or 10 of them depending on design - for DLP there's 2 or 3 depending on design - the picture becomes bleary and nothing will cure that except a professional grade optics cleaning. After that the picture will again show up like the day you unboxed it, new. A new set for the cost of getting in there and cleaning a set of lenses and mirrors.

But be careful - those surfaces are very delicate and any damage that results from inaccurate materials or techniques is instant and permanent. Most lens surfaces in projection types are plastic, and all HD mirrors are front surface. Some are mylar some are glass, but they are all front surface mirrors. As such you must take the ultimate in care - for instance you must not use cleaning agents with ammonia in them as they might interact with the aluminum in the mirroring surface of the front surface mirror in very bad ways. Micro fibre cloths are some of the worst wipes you can use because they have very little absorbency and just swish the dirt around and leave it to dry, with incredible amounts of residue left behind.

I routinely phone coach owners in the proper way to clean their optics without any resulting damage, it has become something of a staple in my calibrations and my routine. During calibrations I always make it available as well, when I am on location with their sets.

Please take a strong look at your projected picture and see what I am talking about.

Mr Bob