DIY Video Projector

[Myren]

SuperDave: i was seriously considering getting nickle plated electroforms made, then plating them with a cold-mirror reflective coating. that would've been so sweet. but i think i'd have to contract someone out for it. is there any way to do DIY electroforming?

marklar: fiberglass would be really nice. any suggestions for getting the reflectance you need?

darth willis: most of the light being focused in the center problems originate from the use of the fresnel. switching to a light gathering method which is uniform fixes all problems. ellipsoidal, if deep enough, is nearly ideal.

myren

[tomithy83]

xblocker
think of an lcd or any peice of glass as a plano-plano lens and any thing that light (even air and the water inthe air) acts as a lens

mountain
just how many led's are in your machine? i dont pretend to understand how your setup is made but your pic looks like 1 led to one color pixel mabe if someone else explained it in laymans terms? please

[oftheend]

Yeah!! Got my 250 watt MH today. I am testing the fixture right now, on the floor. It is a bright sunny day outside, but when i turn this thing on, it flushes all the daylight out of my room. It is brighter than the amount of daylight coming into my house, and i have a lot of windows. The color of the light is ever so slightly more yellow than daylight, nearer the color of the halogen worklight I was using. The halogen light rendered the colors on my panel perfectly, So I am sure that once i rework my box to accomadate this lamp, I will be styling. Sorry, no real useful info yet, but i am excited. I will share when Tests are done!!.

[tomithy83]

ok sutpid question some professinal projestors have a functioin so that when you place the projector below or above the center of the image is still square how do you compensate for this?

[SuperDave]

Myren...I know that DIY electroplating is fairly simple...I forget what liquid you use but you give one object a + charge from a battery and another object (I also forget if you object or metal source get then + or - charge) and place in a bath of the solution. Let it sit and voila....It's supposed to be quite simple (like a 6th grade science experiment).

As far as electroforming goes...I think it is VERY close to the same process...only instead of a thin film covering the object you get a thicker metal layer that you can remove. I really didnt think about this because I figured if I could just form plastic (or fiberglass) reflectors and electroplate (which I know I can do on my balcony) the reflectors would be quite lite. A reflector made from electroforming is actually solid metal (if I'm not mistaken).

I found this link when looking for a DIY electroforming site...although it doesnt supply DIY info it does explain it a little and DAMN they are producing EXACTLY what I want...At least it sounds like we are on the right track. Take a look at those reflectors... almost exactly the size and shape I plan on making...
http://www.optiforms.com/what.htm
I'm getting all excited again.

Later,
Dave

[Scot_lad]

Tomithy - I think what you're referring to is when the projector is placed at an angle to the projecting surface. This produces an image which isn't square on the wall. It is in fact the shape of a keystone, which is the name of the top stone in a brick archway.

Anyway, to overcome this, the image which is being projected has to be altered to compensate for the keystone shape on the wall. Imagine the image projected is wider at the top than at the bottom. To compensate for this you have to change the image on your LCD or whatever to have a wider bottom than top, do you see what I mean?

This is a bit difficult on LCDs or DLPs because they are of fixed resolution, and you end up with a final image which suffers from the same problems as when you try to stick a 1024x768 image on an 800x600 LCD by squashing it. I think you get the picture.

On CRTs they have no pixels, so the problem wouldn't be so apparent.

[jjasniew]

Superdave; Myren's going to go nutz when he sees that!

A link for paint-on screen material -

http://www.goosystems.com/

[jjasniew]

Scot_Lad

Your buddy doesnt want my cheapo (not suitable for panel) OHP?

[oftheend]

Keystone:

Theoretically you could tip the lcd a bit. You would most certainly lose a little brightness, and i would say tipping it more than 5-10 degrees in any direction would have a significant impact on the image quality, ie. uniformity of brightness. You might compensate with a change in the position of the reflector, but in any case i think you would lose brightness.



My first test with the new 250 MH is done... I am very happy to report that the image is MUCH brighter. I tested during daylight, and the image produced was near as bright as the image produced by the 175 MV in darkness, and the colors are much, much better. (i can see red again!!) This test is using my old reflector, the coffee can parabola. I have a new reflector built out of aluminum roof flashing, I just have to fit it inside the case and cut around the bulb. I was just eager to test. So, at the moment, the light leakage is incredible, The area of the projector was lit brighter than ambient daylight during my test. I am willing to bet that once I contain the light, add polarizers, and either paint my dark grey wall or make a screen, that this image will be watchable in ambient daylight. It is near so now. Directing all the light to the lcd should increase brightness ~25%. (this is estimated by simply covering the open top with a blanket, a no-no as far as fire concerns go.) According to the info on polarizing recycling, a good setup can yield a 45% increase in brightness overall. I cannot wait until i test at nightfall.

[xblocker]

There exist 2 types of keystone correction.
The first what scot_lad described is the digital correction. The second is the optical keystone correction, which comes from photographic techniques.
Here comes the Schleimpflug condition into the game. Scheimpflug discovered some laws concerning Off-axis imaging, which is also usable for projecting. He statet, if the object-plane, the lens-plane and the image-plane are meeting in one point, then you have a sharp image.
Optical keystone correction cannot only be done with LCD PJs, also many high end OHPs have it. Digital correction alone can only correct the trapezoid image in off axis projection, but cannot sharp the image.

xblocker