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Cleaning the Optics/Lenses

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Tips from Mr Bob, Tom Herman, and Guy Kuo.

"What is dust?

Dust is thousands of tiny little refraction lenses, each with the dispersing quality of a dum-dum bullet. A coherent, otherwise highly directional ray of light hits a dust particle, and a bunch of it gets scattered in a hundred different directions. Multiply that by the thousands of tiny little dust particles found on the typical objective lens after a year of viewing, and you have unwanted fill-in: the phenomenon of otherwise coherent, highly directional light rays being towed off course in a hundred different directions and going where they're not supposed to go -- notably, into dark areas.  If all pictures were bright pictures, with no dark areas, there would be no problem. But since "depth" in a picture relies heavily on dark areas to separate the light areas accurately, accuracy in dark area reproduction is essential in capturing the 35mm film experience in RPTVs, and to give a sense of depth and realism to the scenes involved. Not to mention maintaining in the RPTV's projected image a "like new" viewing quality on a constant basis.

Granted that though the positioning of these particulates is indeed out of focus along the light ray path, the effect is still the same--haziness around bright objects, rather than whatever it is that is supposed to be there, around those bright objects.

If what is supposed to be there is detail in dark areas, well, too bad. No can do. With haze caused by dust, areas are either light or they're dark and smeary, with no detail possible in the dark areas. It doesn't take much to compromise detail in dark areas--they're very delicate, being dark and relatively hard to see already. With a coating of dust, dark areas just look "smoked out".

Ie., it looks like you're viewing something through smokey glass. Not "smoked" glass--that would simply be clear but darker. No, like through "smokey" glass--glass covered with soot, which is thousands of tiny little black dots. Only in this case, it's thousands of tiny little gray dots. Either way, detail capacity--and therefore depth perception capacity--in dark areas is seriously compromised and stomped on, by even the lightest coating of dust. And it gets worse, year by year, with the viewer staying acclimated to a TV picture that just seems to be "getting old". Nep. Just getting dirty.

Through years' worth of gathered dust, a figure skater in pure white, with TV camera looking up at her against the darkened skating rink canopy in the distance, will show up as having a halo-ish glow around her, which wouldn't be there if the optics were clean. Great angelic effect, but indicating lousy optical dynamics!  

All this is in reference to both the lenses and mirrors.

Now let's talk about the just the mirror behind the screen.

If you freeze-frame our figure skater, then go off to a side angle to view the set, and move your head around -- back and forth and up and down -- you'll find that this haziness in the dark areas will follow your head movements at half-speed, which is the image being caught up in the smokiness of the mirror behind the screen -- rather than the image bouncing off the mirror cleanly and invisibly, as it's supposed to do. In really bad cases, you'll actually get a slightly different view of this haze with each eye. The haze will then be in 3D, and your eyes will be slightly confused and fatigued, because of the parallax directionality involved in your 2 eyes seeing slightly different images, because of the 2 different angles your 2 eyes see from. Obviously, the final viewed image is on a flat plane, and meant to be viewed as such. With a dirty mirror 2 feet directly behind the screen and visible, you're seeing the messiness in 3D, which is definitely not the best way to be experiencing 3D in video viewing.

With crystal clear optics, the mirror is totally invisible, and there's nothing but absolute black in the dark areas behind the screen's picture, where whatever is back there in the optical cavity -- hopefully nothing -- shines through. With dirty optics, the mirror is visible -- blatantly and visibly in the way, in those otherwise dark areas of your picture, along with everything else mentioned above.

This haze effect makes it impossible for any chance at "gleam" in your picture, which is defined as something small and terrifically bright against something either black or really, really dark, with a terrific amount of contrast--translate that as "depth" -- at the edges between the two. No high, sparkling amount of contrast -- or depth -- is possible when there's a hazy glow around anything bright, bleeding off from the edges of the bright object and clouding up the darkness. It's the definition of an un-dynamic picture. 

It's like having an otherwise sparkling audio passage surrounded by hiss, and thus having a really bad signal-to-noise ratio. Very unimpressive, with depth capacity, "breathe-ability", crystallinity, and dynamic punch suffering miserably. That's why I'm so impressed whenever I get a chance to hear the astoundingly expensive sound of Mark Levinson audio equipment -- even with Volume turned all the way up on their 350 watt/channel amps, with absolute silence in the source material, there's not a trace -- even a glimmer -- of hiss.

Amazing. I'm in awe every time I hear their stuff. But I digress...

RPTVs are optical instruments just like telescopes and binoculars and microscopes, and require the level of care and feeding you would give to those, in order for them to perform correctly. Like the above, RPTVs have lenses, mirrors and anoptical cavity in which they develop their magic.

Only, in the case of RPTVs, there's high voltage involved -- created to drive the CRTs, and thus inescapable -- which ionizes the air, statically charging all the airborn particulates, no matter how small, and thus turning the mirror(s) and lenses into powerful dust magnets. That's why new age people types use ionizers -- ionizers are low current, high voltage instruments that charge all airborne particulates, causing them to cling to your walls and mirrors and whatever other flat surfaces there are to cling to, instead of remaining in the air, to get into peoples' lungs. Makes the walls look terrible, especially around the ionizer, but keeps your lungs clean as a whistle.

This high voltage around the CRTs is why these optical surfaces in RPTVs need to be cleaned every year, bare minumum, in normal use -- with Sonys, Pioneers, Toshibas and Philips needing a slightly more advanced job done twice as often, as these brands have buried, secondary lenses that are also exposed enough to attract the dust. Mitsubishis seal their secondary lenses, so that only the upper lens's exposed surfaces need this attention, and thus need be done only yearly.

That's all for now, kiddies, it's taken 2 hours to get this far, and I gots to go. Next installment will cover how to clean these surfaces as often as is truly necessary, thoroughly and without damaging them. 

Stay tuned. After all, it is Friday night...

What?  Use Paper Towel to clean the CRT/lenses?

Yes, I do use paper towels, and I never have to worry about scratches, because it's all in the wrist. The only caveat is to NOT use shop towels -- ANY additive, like lanolin, will continue to wind up smeary, long into the night. Hours later you'll still be grinding away, trying to get your your optics clean, and you simply never will, with those kind of towels. You'll just scratch up your optics. Make them plain old paper towels, made only of pure paper. (Having the kind that has printed patterns on them doesn't hurt, any more than newsprint on newspapers -- which I've always found to be the BEST way to do windows. Newspapers are not the best way here, tho, because of the mess they leave behind--some of it floating in the air -- which paper towels do not. Same argument for not using Kleenex, even tho technically it would seem to be softer than paper towels.)

The way to make sure there is no scratching done is to make sure that the matting of dust is soaked and COMPLETELY HYDRATED AND SUSPENDED IN THE LIQUID used as your cleaner, before any removal is done. (WITHOUT letting any liquid get down into the multiple lenses inside the lens barrel. Such liquid will evaporate and condensate, fogging up your internal lenses.)

During that removal of your contaminants, only go in one direction -- towards you and/or upwards -- during the first swipe -- don't go back and forth, over and over, grinding the particulates into the glass -- or even more sensitive, plastic -- lenses. Just go in one direction, towards you, carefully but swiftly, mildly back and forth in a progressively closer-to-you zigzag motion, as a GATHERING of the grit -- possibly even rotating your towel up a bit as you go, continuing to expose only fresh paper to the optical surface.

All RPTVs need professional optics cleaning at least once a year under average use. At the risk of disagreeing with Louis in public, and after having talked with him about this very subject by phone, and after having had him tell me that he calibrates chiefly brand new instruments, which of course don't need optics cleaning yet -- I'm going to make the following statement:


That's COMPLETELY, underlined. I have made the same statement a number of times lately on the DTF.

NO MATTER WHAT AGE OF RPTV. This is just as true 5 and 10 years down the line, where your RPTV can still continue to look better than new, if you include this step as part of your professional-grade calibration.

This is aside from the stray dust that immediately gathers on the lenses before you even get out of the optical cavity after a good lens/mirror cleaning, if your TV is still on while you're still in there. Anyone who has been inside their optical cavity with their TV on has noticed this, if they've been looking. The stuff floating in the air is GREEDY for your lenses, and gathers on them there, right before your eyes.

You see, high voltage statically charges ALL the particulates in the air, turning your mirrors and lenses into powerful dust magnets. If RPTVs didn't have HV as part of their process, I'd be aggreeing with Louis, for the most part, about staying out of the optical cavity for the life of the instrument.

But not here. The constantly present HV during TV operation causes the repeated and constant need for professional optics cleaning in RPTVs.

If you don't believe me, get inside and take a flashlight and shine it onto your lenses, shooting in from the side. Then lick your finger and draw a happy face in what you see--looking at it, again, obliquely, as from the side or front, but at an angle, rather than straight on. Do this BEFORE the cleaning process itself, of course...

I wrote a post on the DTF earlier this year on this subject, and it continued for weeks, with many viewers writing in to say how incredible the change in the picture was, after the in-depth lens(es) and mirror(s--sometimes 3!) cleaning they gave their RPTVs upon reading everything that was eventually contained in that thread, written by me and by others also.

Unfortunately I'm presently in Portland on my monthly visit, where for a week at a time I contribute my share of the 24/7 caregiving my Mom with ALS requires--my partners in crime, of course, making sure I have the space to take time off for the occasional Portland area calibration that comes in now and then--or I'd give you the address, which of course is safe and well in my home computer in California.

Does anybody out there have the address to that thread? It might help some people here.

Good luck. It can be done, very simply, and is worth its weight in gold in the picture improvement it makes.

Mr Bob

PS -- I try NEVER to touch the inside or outside of the fresnel and/or lenticular lenses, unless absolutely necessary. They do NOT regularly need maintenance, and are extremely sensitive and fragile. The vertical ribs on the fronts of the lenticulars, in particular, are extremely vulnerable to residue from any liquid that touches them, no matter how professionally accepted a cleaner it is.

The most I would normally do in any calibration would be to get the cobwebs off the inside of the fresnel and the inner optical cavity by swooshing a piece of the paper towel around in a circular motion, to gather it around the paper towel; and perhaps GENTLY wiping the inside of the fresnel down in a VERY light and gingerly fashion with a DRY terrycloth towel. And that's only if I can see dust on it while looking at its surface from the side.

And Louis WILL agree with me on this: NEVER touch a mylar mirror. They DON'T attract dust statically like glass mirrors do, therefore don't need cleaning in the same way, and are levels of generation -- exponentially -- more sensitive than glass to being scratched."

More Tips from Mr Bob:

"I have had to disassemble several sets of lenses in the past few years, when after spraying them with my cleaning agent, I didn't "dive, dive, dive" with my towelling to the bottom-most edge quickly enough, and the result was condensation on the inside lenses. They really should seal those lenses, but many of them are more than susceptible to the cleaning fluid leaking in. I had to actually take each lens apart, exposing the several-layer lens pack inside.

If this is just debris, and not caked-on, dried-on layering of problematical "stuff", as happens on the outside of the lenses--and it would be hard to get lots of problematical stuff inside there--I would suggest simply using a photographer's brush, instead of actually cleaning anything. If it's just loose debris, this has to be the least invasive way to handle this, next only to simply using compressed air once inside.

Remember also, the debris you are seeing is most likely being magnified by the other lenses, and may not be that big a piece of debris after all.

I had to open them up and use a hair dryer on the condensation, but I did not extend my invasion to include cleaning, because the lenses were simply fogged up, and drying them was all that was necessary. After all, if it ain't broke, don't fix it! Too much can go wrong in there, in situations like that.

If for any reason you have to remove and deal with any of the individual lenses, be sure to do it ONE LENS ELEMENT AT A TIME, and don't get the lens reversed when and if you lay it down.

Remember, if you do mix any of them up, or get any of the elements in backwards, you won't know it until you put it back on the unit. And to get it right if it's wrong, you'll probably have to take another one apart, just to have an accurate model to work from."

Quick Tips from Tom Herman

"As previous experiences indicate (fluid inside lens), safer way to clean an RPTV lens is to use same techniques as with an SLR camera's lens.

For small areas like a lens, I've had good success with Kodak brand lens tissue & cleaning fluid. It does shed lint, but the lint is large size & easily blown off with a can of compressed air.

  • apply cleaning solution to the cleaning TISSUE, NOT directly to the lens. Crumple/ fold/ "Poof up" the tissues, so that finger is not pressing directly against lens.
  • lightly dampen the tissue, don't get it dripping wet.
  • clean/wipe lens in circular, outward, "spiral" direction, center to edge, with tissue.
  • dry lens with fresh tissues, again spiraling outward. repeat drying as needed."

Tips from Guy Kuo:

Probably the two most likely things to help your situation are to clean the optics and line the interior of your RPTV. Both of these require removing the front screen and may void the warranty if that is an issue. 

The following information is applied only at your own risk. It's best to have someone who has done this type of thing before help. You should be cautious and must take care to avoid damaging your display or injuring yourself. There are dangerous voltages inside and the optics are easily scratched.

Removing a RPTV front screen usually requires removal of the front speaker grill and then the screen fastening bolts holding the bottom of the screen. Then the screen swings out slightly and is lifted off its mounting hooks which secure the top of the screen to the cabinet. Careful, sometimes there may be wires attached between the screen and the cabinet.  Once opened, inspect the mirror and lenses with a flashlight. An RPTV can attract a surprising amount of dust and grime. This scatters light and creates a hazy or haloed image. I don't smoke, but even so I needed to clean my lenses about every 6 months. A CRT is basically a big high voltage dust collector. The attached optics share in the bounty. 

The lenses and mirror are very fragile and easy to damage during cleaning. Front surface mylar mirrors should NEVER be sprayed or wiped down as they will probably be damaged. Use a soft, clean brush to lightly waft off dust on such a mirror, but do NOT use any liquid cleaners on a mylar mirror.

A camera lens dust blower should be used first on the lenses. That removes some of the dust. Canned air is okay if it has been dehumidified. Do NOT use compressed gas cleaners which are not air. If you spray them improperly, the liquid may come before it has a chance to vaporize. If the propellant hits the lens in liquid form, it will mar the lens surface.  Once as much dust is removed as possible, see if a very gentle wipe of a fresh microfiber lens cleaning cloth will do the trick. Use a virgin portion of the cloth with each pass. Remember, once scratched, the lens will never be quite the same again. 

If a microfiber cloth is insufficient to clean the lens, then resort to a cleaning liquid. Stay away from ammonia containing glass cleaners as they can strip away a lens antiglare coating. I like Lens Crafter's lens cleaning solution as it does not dissolve antiglare coatings. Their lens cleaning tissue is also lint free and less prone to scratch a lens. It is best to spray the liquid onto your lens cleaning tissue rather than directly on the lens. Otherwise, you risk excess fluid going inside the lens assembly. Use lots and lots of tissues so every stroke is with a clean section of wadded tissue.

I prefer to start and lens center and work outward. During the stroke, I roll my hand so the soiled portion of the tissue is lifted off the lens surface. This reduces the amount of grinding that the grit does to a lens and also brings a dry portion of the tissue into contact with the cleaned area to wipe it dry. If you don't end up with a pile of used lens tissues, you probably are not changing tissues often enough. Seems wasteful, but so are scratched up lenses.  The last note to know about lens cleaning is that you should expect cleaning to eventually scratch a lens. That is why it must be done very carefully and only when necessary. If just dusting with a blower is enough, don't wipe down the lens.

Sometimes the concave lens at the bottom of the lens assembly is coated with dust. That necessitates removing the lens for cleaning, but doing that almost always means your convergence will be thrown off so I don't recommend that be done unless one is willing to reconverge a display. 

Regular tissue paper is NOT a suitable cleaning paper unless you like lint and scratches. Use a CLEAN microfiber cloth to wipe the lens very gently.

More tips from Guy Kuo

Don't scratch the lenses!!!! Not only can you scratch the lenses but use of the wrong cleaning solution can remove antiglare coatings. Once damage is done, one isn't always lucky enough to get a replacement lens.

William Phelps has long used a custom cleaning solution on many many projectors...

1 drop dishwashing detergent (not soap!)
(or Kodak Photoflo if you have it)
1/3 cup 99% Isopropyl alcohol
1 2/3 cup distilled water

In terms of how to clean the lens, it is best to use an air blower and gentle, soft brush to remove loose debris. If that isn't sufficient, then a microfiber lens cleaning cloth is the preferred cleaning wipe. Dampen the cloth with the solution. Do not spray the lens directly or you risk the solution seeping into the lens assembly.

Wipe with a light touch always rolling the cloth so a new, clean portion is in contact with the lens. Start at lens center and wipe radially outward. Each time be sure to use a clean section of the cloth. Wiping with a dirtied portion of the cloth will scratch the lens. Excess pressure will scratch the lens.

Use another cloth once the first one is soiled. They can be washed, but don't use a fabric softener!!!!

Another alternative to the microfibre cloth is lens crafter's lens cleaning tissue. It is a cotton tissue which is less likely to scratch than wood pulp based normal tissue. You have to be more careful with the lens crafter tissue than with a microfiber cloth, but its disposability helps encourage use of MANY sheets to avoid reusing a soiled portion. Do not use normal tissue or paper towels as they can scratch the plastic or coatings. Stay away from the onion skin-like lens cleaning papers. They are inadequately absorbant and tend to grind grits into the plastic lenses.