DIY Video Projector

[CLY]

hi all!

check this out!

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=1348545696

[DPW666]

Hi,

Ive been reading this thread since it started and decided to register now. I got a Proxima Ovation 820 because I wanted to go the OHP way. I borrowed an OHP at school to try out the panel. First thing I saw was the screen door effect. It wasn't that terrible but I am more of a CRT projector guy because of their "film like" quality. I have a 12inch IBM monitor here and boosted contast and brightness to max. Tried it with the lense from the same OHP I borrowed and I must say that the quality was much better. Ok, I can't use when there is ambient light but in total dark the image is superb. People that tried the 100inch tv projector with the fresnel lense say that the image lacks of brightness and sharpness. This is because a fresnel lense isn't as good quality as a glass lense. Now that I found my true way, Id like to trade my LCD panel for the head or lenses of an OHP. It comes with a travel case, the remote the cable and the power supply. I live in Montreal, Quebec in Canada. E-mail me at mariano.janeiro@videotron.ca if interrested

[jjasniew]

Oh, I just had problems with the particular one I got. Stuff like it syncs to 74hz, but not 75 - without all these wavy modulation lines showing up.

The color controls dont work in VGA mode. Figure they would do it on a top panel.

The image, while fast and with really accurate color, has these funny artifacts, kinda like lines following various contours. Edges of objects can be "venetian blind" a bit - but for all I know it's the panel being more accurate with my DVD playback on my PC, w/o any Dscaler...

Havent tried it yet with S-video or composite.

Has a bad pixel, for my $225...more than 1/4 of my CRT purchase!
It's for sale for what I paid -

[MuzzMan]

I don't know if someone can help me, my lack of optical knowledge is really hurting.

Up till now I have been using a fresnel lens as the projection lens for my 5" lcd. Now I am redesigning the setup so it is rear projection and thought the 4" Delta77 compound lens I have would be better quality and more suited to the short throw needed (about 70 to 100" or so).
I thought that the "projection lens must be bigger than LCD problem" could be avoided if one or more fresnel lenses were used on the light source side of the LCD in order to converge the light, so in simple terms it all fits through the projection lens. However my really basic experiments so far have shown that I still need to have the Delta77 lens really close to the LCD (about 15mm away), and even with trying a fresnel lens at various distances behind the LCD I can't get anything better than a weak circular image that fades at the edges.
I have seen some peoples photos who are obviously using some sort of small lens as the projection lens, I assume they are using lenses intended for ohp's which might have longer focal length than the delta77 which I think was intended for CRT projection.
Am I stuck with using a ohp fresnel lens as the projection lens? I assume the problem is even worse with bigger LCD's.

[Undream]

well, you are pretty much right. we might have to use either a plano-convex lens, or bi-convex lens (OHP lens) instead of a delta or fujinon in order to capture an LCD that is larger than the diameter of them. (see attached pic)

however, if there is some way of using both of them -- the delta AND a bi-convex or plan-convex, it might work. But remember, you dont need a fujinon or delta to complete the project, and, if I was going to use both a plano-convex and a fujinon, then, it would only be to achieve a shorter throw distance.

[gray]

MuzzMan,

As you may know the majority of lens are made as a section of a sphere. The simplest lens use can use to project an image is a converging len(like the ones form an OHP) It is flat on on side and convex on the other. The curved surface is the section of the sphere, the center of this sphere is called the center of curvature.

If an object is past the center of curvature you will form what is known as a real image.A lens can form two types of images, real and virtual. A real image will apear on the opposite side of the lens(projected),and will be inverted. A virtual image appears on the same side of the lens as the object, can not be projected, and is not inverted. The image you see when using a magnifing glass is an example of a virtual image.

So, now as we move our object from beyond the center of curvature and closer to the lens the image becomes larger, untill we reach the focal length of the lens, at that point the image becomes a virtual image and of no use to us for this application.

When you put a fresnel in between the light and lcd, you are not trying to make the light converge onto your lens, in fact you dont want the light to be anything but parallel rays of light hitting the lcd at a right angle



"projection lens must be bigger than LCD problem"

This problem you are refering to will real only apply to complex lens like the delta or equivalent. These lenses were made to save space, the designer wanted to put the lcd as close to the lens as possible. Unless you have an LCD of a size designed to work with the complex lens it is going to be a pain in the *** to get your delta to work. It may be that your 5" lcd is just a bit too big.

Try using a convering lens. It is more efficient in passing light and will result in an image with less aberations then projecting with a fresnel, and you wont suffer from the constaints of the delta.

Good luck

[ravide]

Gunawan,
Thanks for the excel w/s.
btw, i noticed that changing the focal length of the lens does not alter the image size unless the
distance of the lens 2 to the virtual image is changed or the distance of lens 1 to lcd or lens 2 to screen is changed. Does this mean that any focal length lens can be used as long as the distance mentioned above are appropriate, you will get the desired image size. I thought that the image size projected depends on the focal lengths of the lens, ie.
Focal length lens 2/focal length of lens 1 = Magnification factor.

correct me if i'm wrong...cheers

[SuperDave]

Well... I spent most of the day looking for a new(OK...new to me) and didnt have much time to work on my projector but I did get some done...

Since I got a sample picture with my VG150 the other day I decided to start working on my new lighting/projector setup. I have a poor OHP so this is my next step. I spent a couple hours deciding how I would build my next-phase setup. After I decided what I wanted I spend 2 hours searching HomeDepot for my parts.

First I built a GFI box(ground fault interruption I think). Basically this is going to help me not kill myself. It's basically an extension cord with the same concept of the outlets in bathrooms that have the test/reset buttons. This took me a while to make sure I did correctly since I dont have a strong electrical background.

Next I decided it was time to attach a plug to my Mercury Vapor light. This is the MV vapor light people have been talking about from Home Depot (although I've had this in storage for years). It is designed to attach to the top of you home and connect directly to conduit wire. I simply bought a 14 guage outlet cord with the 3 wires exposed. I hooked it up as it described to do and treated the cord as the conduit. When I was all done (Being careful not to let the wires touch the balast -- make sure you dont let this happen if your one of those using this light) I plugged it into my GFI-extension cord and watched. It started out flickering a little and was VERY dim. The info on the ight says it takes 2 minutes to start up and this is true. It slowly got brighter and brighter for about 1.5 minutes....
and then it went out...
I took it apart because I smelled like I might have melted a wire on the balast but saw nothing and put it back together and it worked again... I later realized it was because it got my room SOOO bright the photo-sensor on the lamp shut off. I turned the lamp back on and watched over a few minutes as the previously dark room (this was at night) began to GLOW!!!!. The entire corner of my aprtment began to Glow even with the other lights on.

This lamp is amasingly bright. I am VERY excited about hooking everything up tonight (or at least as much as I can). There are a few drawbacks though....
1) the lamp and balast assembly are quite large. I will post pics tomorrow showing the size...but the light is probably close to 8 inches...give or take a couple.
2) the light seemed to have a slight shade of blue... Dont know if thats because I'm comparing it to my yellow lights at home or what.
3) when I place my fresnels from my OHP in front of the lamp and tried to fucus the light on the wall I continually got what I think is refered to a hot-spot. You could see bright spots kinda like when you shine a flashlight at a wall.

Well I will try to post as many pictures as possible...and for those that didnt see my pictures of gutting my VG150 LCD monitor you can see them at:
http://www.csun.edu/~hbpsy028/projector

Sorry for the long post...
Later

[fender4]

gray,
Thanks for the optics clarification. I know that I have struggled with those concepts in the past, so that should help many people here.

SuperDave,
Good luck with your MV lamp! I haven't been successful with it in my configuration (non-OHP), but that is because I don't have a proper reflector for it. I, too, had to cover the photosensor with tape. It looks like it can be bypassed fairly easily. I extended the wiring to the socket to facilitate moving the bulb away from the ballast. This might be necessary to mount it in an OHP. I look forward to the pics...good luck!

-f4

[jjasniew]

Looking at your photos, I see you're working on carpet. There is a chance that you could generate electrostatic charge, then touch your exposed panel electronics and <BAM> - dead!

You might want to use the practice of always temporarily touching metal that is connected to earth ground, before touching your panel or any driver board. Or make sure you only work barefoot...

Opening these displays leaves them vulnerable to ESD and the possibility of destroying part of the panel electronics this way is real. Especially if the humidity in the room is low.