CurtPalme.com Home Theater Forum

[garyfritz]

[cmjohnson]

[piratepowwow]

It can be done, and it can be done at home without huge capital expenditure.

The question is, are you up to the task, cause it's not going to be easy! But if you own a CRT projector, there is a higher than normal chance that you aren't a big fan of doing things the easy way ^_^

There are at least three design paths you can go down, each has strengths and weaknesses:

Prisms

Lenses

Mirrors

Both mirrors and lenses can be cylindrical/elliptical/parabolic/catenary and whatever else you want to call it.

I think CAVX's aussiemorphic lens has already proven that it can be done by the DIYer. But, again, I wouldn't say he found it particularly easy.

CAVX eventually abandoned the prism lens not because it didn't work well, but because each 'lens' had a "sweet spot" and was not as adjustable as the cylindrical lenses he is now using.

Going anamorphic will certainly exacerbate the edge focusing issues(and other issues as well) we have with CRT PJs, but there are things that can be done to help cope with it, such as curved or spherical screens. If you don't have lens flapping on your projector, you can pretty much forget going anamorphic.

Questions we must ask ourselves:

Why do I want to go anamorphic in the first place, what is to be gained?

I personally could care less about making the screen wider, I just want to use the most phosphor I can possibly use for the majority of the content I watch, which is 16:9.

I don't subscribe to either CIA, CIH, or CIW. I want my 2.35:1 content the same width as my 16:9 content, and I want my 4:3 content the same height as my 16:9 content. Fortunately, this is how HTPCs generally display their content by default.

Supposedly by using more phosphor, horizontal lines will resolve better, and less brightness will be needed so the tubes should last longer. If using zero-angle projection you also get a perfectly even wear pattern(only if 16:9 content is used exclusively).

What should my budget be?

For me, the cost should be less than the cost for a new set of tubes OR about half the cost of implementing blending, whichever is cheaper.





I don't doubt it for a second that someone CNC'd custom elements for their G70 - because I've done stuff like that before. In this day and age, advanced manufacturing techniques are becoming more and more available. Heck, there are clubs of makers these days that register what tools they have in there area and let others use them, much like a public tool library. Large, high precision CNC mills are going for less than $10k, and lathes(albeit small) are going for less than that. The average guy even has access to laser scanners to scan for surface imperfections, and 3D printers for rapid prototyping, or making mold reliefs.

[cmjohnson]

Having CNC machining capacity does not mean you can make optics. Far from it. Any optics of high enough quality to be used on our projectors at HD resolutions would have to come out of an optician's shop and the lenses would have to be accurate to within a few millionths of an inch to meet the resolution specs that the application demands.

CNC machining capability is not equal to the skills and tolerances required of an optician. They are two completely different disciplines
and the optician must routinely work to a dimensional accuracy standard that would frighten most machinists and is beyond their capacity to achieve.


CJ

[Kiev Savoie]

[Kiev Savoie]

[cmjohnson]

Right click on the photo and you'll know.

But those lenses are TINY, maybe an inch square.


You will spend THOUSANDS of dollars per lens IF you can find someone to make them AND they will have to be custom engineered,
and that probably means sending your entire projector to their optical engineering department.

If it costs less than 15,000 dollars to get a set of lenses made, I will be very surprised. If you can afford it, then good for you!


CJ

[piratepowwow]

The first thing that comes up when you search for DIY Anamorphic Lens is this: http://www.zuggsoft.com/theater/prism.htm

A man who acheived what I would call satisfactory results(chromatic aberration aside) using glass trophies as prisms. Not $15k custom lenses, not lenses ground to within a few millionths of an inch, but $29 glass trophies.

Folks have been grinding their own telescope mirrors for years...

[garyfritz]

Interesting. But note he's doing that with a digital projector. "Tropies" big enough for CRT lenses would probably run you a LOT more than $29, and you'd need 6 of 'em...

[Nashou66]

[piratepowwow]

Cheapest blending I have heard of is using an Nvidia Quadro series video card that has edge blending capabilities designed specifically for blending projection displays. You can pick one up for less than a couple hundred bucks.

Then, of course you would need a projector that is capable of convergence on green. Probably just one of a two-projector setup would need convergence on green.

[Spanky Ham]

Here is all you need to know for the anamorphic lens/mirror option:
http://archive2.avsforum.com/avs-vb/showthread.php?t=597173

FYI, Chiem is a physicist from Princeton.

Here are some other notable threads that I came across looking this up:
http://archive2.avsforum.com/avs-vb/showthread.php?t=596881
http://archive2.avsforum.com/avs-vb/showthread.php?t=619600
http://archive2.avsforum.com/avs-vb/showthread.php?t=626698
http://archive2.avsforum.com/avs-vb/showthread.php?t=633597


Pow,
I don't believe the Quadro has a soft edge blending feature in the drivers. If someone wanted to try a hard edge blend, then the new ATI/AMD cards might work.

[Kiev Savoie]

Well Nash, the price of blending has definitely gone down, but until it's in the the hundreds of dollars range as opposed to the thousands of dollars range it will still be out of my league. It's killing me just trying to get a single Lumagen HDP scaler. they never seem to pop up when i actually have money!

POW, I'm not sure how it will all turn out but if you want to run some experiments, i just recently acquired access to an old TV repair shop that has room for a quick and dirty projection bay. We could use one of my spare G70's, that way our own setups don't have to be interrupted. I don't know how successful we'll be but, it could be fun and i'll bet we'll learn quite a bit about optics!

[CasetheCorvetteman]

If anyone here has ever opened up a rear projection CRT television, they would have seen 2 things, the mirror is dead flat, and in better quality sets is made of surface reflective plastic instead of glass where the image has to go through the glass to get the the reflective level and then back through the glass, and also the tube faces are not using full raster, they have the same or simular width to the 4:3 version of the same or simular set, and have the vertical size reduced.

Dont know about every single set, but i have compared 2 Panasonic GAOO sets side by side, TX-51GF85-H 51 inch 4:3 and TX-47WG25-H 47 inch 16:9, both sets have the same 7 inch tubes, both sets have the same lenses, both are LC and colour corrected in red and green, the screen width is the exact same on both. The raster usage is about the only difference once you take the screen and lenses off and look through the c-elements.

Apart from all that, every other RPTV ive opened up has a simular mirror, and if its 16:9, its using a letterbox format on the tube face.

[cmjohnson]

Actually, the BEST RPTV sets, from an optical quality perspective, use a first (front) surfaced glass mirror of high quality.

The modern trend toward the use of tensioned Mylar film over a frame to make a mirror is done because it makes a mirror that doesn't
break and create a safety hazard when the set is scrapped, eliminates the use of more expensive glass mirrors, and it does a very good
job so long as the mirror is clean.

Drawbacks to the mylar mirror: Almost impossible to clean without damaging the silvering, susceptibility to vibration modes which
make optimal focus in some parts of the screen impossible, and second best reflection performance as compared to good first surface
glass mirrors. Though the surface is good, is not as perfectly planar as a good piece of glass.


CJ

[CasetheCorvetteman]

Thats true indeed, ive never opened one up with glass in it though, i think i remember reading somewhere that the Toshiba CRT RPTVs had glass in the 90s sets ( although the Toshiba i opened up was a 2003 model and had plastic ) , they were way out of my price range when i bought my first of the 2 Panasonics.

[virusc]

Most of the better RP TV's from the early 90's up had first surface mirrors. Mitsubishi's entire line used them as a selling feature early on and until the end. Pioneer, Panasonic, Toshiba and most likely others did as well. Pioneer would also list all glass lenses and corrected c-elements for the elite sets. I once had a Mitsubishi display at the store I worked at showing the difference and it was a huge difference.

[cmjohnson]

The mylar mirrors are a fairly recent introduction. Glass was the standard until the early 2000s when mylar started to get used.

It's also very cheap to make a mylar mirror.


CJ

[Kiev Savoie]

yeah, goodluck finding a big screen from that era though. Most of what comes in for repair and troubleshooting at the store i work at is only 4 or 5 years old at the most. I've been very disappointed at the pickings.

[CasetheCorvetteman]