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Originally Posted by flibble I just found this thread, hopefully not everyone has packed up and gone home;p
I also saw the thg guide, and used it to make an lcd projector. The final result is ok, although less than optimal.
The screen we got, a compaq TFT 450 15" LCD was about £50, minus psu which we made from a computer PSU (these screens have funny ps2(mini-dimm) style power connectors. The screen looked ok for our intended use (mostly movies), but turned out to have a largeish control board which wired into the screen with 4 very short ribbons, two per side, for a third of the way along the widest sides:/ Not having the ability to send back the lcd's, or the resources to buy a new one, we set the monitor to 800x600 and moved the displayed image as far left as possible. This works reasonably well, no visable pixelation although the far left and right bits of the screen arent viewable (about 10%). The pc its running off has a matrox g400 in it, so software screen shifting isnt really an option.
The projector was an 'Elite vision' ohp with a 250w halogen bulb. Sadly, we bought it without knowing the bulb's wattage, although there wasnt anything good/reasonable on ebay at the time.
We bought a screen from ebay too, not sure of the brightness, I'd guess at maybe 1.1 or 1.2.
Overall, the project has been fairly successful, but luck hasnt been on our side all that much. I'm weighing up the idea of improving it, either with a better screen with a less restrictive ribbon placement, a 400w ohp from ebay, or perhaps replacing the light fitting with a more powerful metal halide lamp, as you did, Chernobyl. I've got a couple of questions about the light though:
Is having a triplet lense system in your ohp essential or just really useful if you wish to use another type of bulb? I seem to remember there being a lense above the bulb in ours, but I'm not sure and its not straight forward to check.
How easy is it to modify an ohp to fit the bulb? I dont really have much in the way of tools, but i can normally find a way to do what i need. What did you have to do to fit the metal halide lamp?
Thanks so much 
Dan |
Hi Dan
Yeah, I'm still around if you want assistance
If you need piccys of anything let me know.
Glad you managed to get the project off the ground despite your setbacks.
The triplet lense (edit: this is the Condensor lense not the triplet) is not essential but I do recommend it strongly.
Having a large lense above the bulb catches more of the light that would not hit the Fresnel/LCD. It also spreads the light more evenly across the display area.
Without the lense, you still get a useable picture but it is noticably brighter in the centre / darker in the corners.
The lense you have above the bulb is the one that makes it a triplet lense system (edit: again, this is the condensor lense, not the triplet).
Fitting a new bulb will be a different challenge in each different OHP.
The principle should remain the same, so I'll describe as best I can.
When you get the new bulb, get a bigger rear reflector for it as well.
The one supplied with my OHP was small and gave a poor result, luckily I bought a replacement in case it was needed.
Hopefully your OHP has lever/knob which raises/lowers the bulb to balance colour across the whole screen. The platform the bulb is on will move up and down.
I highly recommend keeping this platform and the lever working. Mount the new bulb on the platform, this will allow you to easily select the height the new bulb will need to be.
If your platform isnt adjustable, you made need to unmount it and make your own height adjuster for it.
I had to remove the entire height adjuster frame and hammer the bulb platform flat using wood and a rubber mallet so the new bulb would fit on it.
The metal platform was placed on an old wooden shelf to protect it and my floor! The flattening was performed by holding a piece of wood on the area to be flattened and hitting that with the rubber mallet many times very hard.
It doesnt need to be perfect, as long as the bulb can be mounted on it.
If your platform is too small to mount the new bulb you will need to extend it.
Drill holes at the mount points for the bulb
Once your platform is ready for the new bulb you need to place the rear reflector, bulb and lense. The distances between them will determine how efficiently the light is forwarded to the LCD.
The focal point of the rear reflector is the 'recommended' place to put the bulb. I found moving the bulb a little further away allows more light to reflect past the bulb onto the lense. You will need to see what works best.
To find the focal point, look into the lense and move a finger back/forward until the reflection of your finger is the same size as your finger. place the bottom edge of the bulb at that height or slightly further away.
The lense on top needs to be close to the bulb to catch as much light as possible, but not so close it impedes airflow round the bulb.
As you can see its not quite straightforward to find the right heights so you may want to make an adjustable mount for the lense. The light can be raised/lowered easily enough with washers etc and the reflector should remain static on the shelf.
Mine is shockingly put together using lots of tin foil moulded into mounts for the lense. This allowed me to raise/squash it very easily to get the heights. Its worked so well, I've left it like that. Someday soon I'll finish the job
The new 250W bulb is brilliant as it is as bright as the old 400W and whites are even brighter. It also runs much much cooler and should be cooler than your 250W halogen.
I removed the OHP glass to get a bit more light as the bulb doesnt produce much UV light. (edit: dont do this, it disturbs air flow in the OHP and probably isnt good for the LCD)
I'd really like to make the screen much bigger than 5ft. Mine should do 6ft easily, but I would recommend a 400W bulb if going bigger (edit: a decent screen is good enough for nearly a 3 metre screen with a 250W MH bulb).
The 400W dont have UVstop at the moment (even when advertised that they do!), so you must use UV protection of some sort. The OHP glass may be good enough for the job?
Your OHP should be fine with a 400W MH bulb as it can remove the heat from a hotter 250W Halogen effectively.
Good luck, keep us informed if you have the time
If you need help, especially with bulb selection, do ask.