There is only so many ways to make a large LCD PJ brighter. I think a large LCD will always look better than a small one for a lot of reasons but the larger the LCD the longer the fl of the triplet has to be to get any kind if acceptable throw.

The longer the throw of a triplet the longer the front FL of the PJ will be and the greater the size of the lamp arc image at the triplet. This is why our PJ are not that bright. The triplet is too small to allow for a large arc lamp or a large condenser or a large reflector system.

Some of us have long rooms and want the PJ behind them. Some of us want to use vary large LCD's like a 21"
Most of us want a PJ that makes a lot lighter.

We can run a real PJ lamp and this will help a lot. The 575 watts lamps look real good for this.

We can find better polarizer’s that let more light through.

Or we can find or make a larger lens.

We can make our own lenses if we use acrylic molding resin. This is a clear glass like plastic that can be used as a lens. It can be poured into a mold and may make for a fine lens. It would have to be hand finished. A plastic lens would not melt if it was large enough so the heat was not contrasted to a small point.

A doublet lens may be sharp enough for our use. A slight softening of the pixels might even be welcome to help lessen the screen door effect as long as it was even across the whole screen. A long FL will help to make any FOV focus problems less.

My first Idea of the size of the lens is a 250mm diameter x 580mm fl doublet.

I know this is huge but it will solve all the brightness and throw problems for most people.

Almost any lamp could now be used.400 watt through 1500 watt. Better yet a large reflector system can now be used. A vary large condenser lens could be used too.

I am willing to get the two masters lens made out of aluminum and we could pull molds off the master. Plaster or resin would work fine for this. It would help to lower cost if the profiles were the same on both sides of the lens, even better if both lenses were the same.

I know nothing about making lens. If we could find the curves that normal doublets use maybe we could just make them larger if they are acrylic.

This would be a group effort the lens designed would be up to you guys. The main goal would be to make the final lens for less than $100 each.

Any Ideas ?
[edit]
A second doublet size would be a 152mm diameter x 390mm fl

Great idea, just wondering if there are any lens design progs out there that could be used?

Maybe some of the following (trial versions that can be used for a short period?):


Prog 1
Prog 2
Other progs
Even more progs
Interesting Link

If you have a ONE lens, Surplus Shed can re-manufacture them to the same specs.

I would think that most lenes are made from stock blanks. Have you ever seen a cheep 10" lens?

I haven't looked for large acryclic blanks yet but it might be worth a try.

Don't know about acrylic but don't they have glass blanks for people to make telescope mirrors with 10"+???

Some looking at the DIY telescope people may tell us a lot about making a DIY lens.

Doublets are pretty straight forward, and easy to make. Triplets are tricky. You need a good computer system to get a clean one. Either way, it takes a lot of trial on which lens will take a full view of the lcd, or it can be blurry on the edges. If you take two overhead singles, and put them opposite, it makes for an ok doublet, but the focal length splits in half about. So for instance if you have two 400mm fl lenses, you will have a 200mm fl lens when making a doublet out of them. I used two to make a 5.6" projector, and it worked quite well. It gives a clean corner to corner 60" projection. Good luck, and it is a lot of trial and error.

I probably don't need to say this, but you can be like me and buy 60+ lenses and then just mix and match until you get what you want.

But...did that work out for you? Do you have a working lens?

I like the idea, I'd definately like a brighter screen to be able to play in a lit room. I'd have to get a bigger hole cutter to make a 250mm diameter hole, but it would be worth it if it was a clear bright picture.

Thats almost a foot long lens! Yikes...

Have you contacted any lens manufacturers? By the way, I just did a few searches and found a good list of plastics manufacturers or distributors http://www.injection-molding-resource.org/ And I found specifically acrylic molding resin here http://www.plexiglas.com/altuglas/plex1.cfm . I'll be keeping an eye out on this thread!

I would love to be involved in this. But I don't have the skills to help with the optics. I am OK at polishing, though, and it would be fun to be an early-adopter and see what happens.

Uhh, this seems a little overkill. Why not just use a couple more frenels to tighten the light coming into the triplet?

Something like this:



The added fresnels (in blue) would tighten the image down to all fit into the triplet.

The dashed line is the original path of light without the added fresnels.

heh...isn't 4 fresnels over kill?
The reason that's not ideal is because more fresnels = more light lost + more calculation.

And actually...I'm betting if we can make a good elliptical reflector combined with a large lens...we wouldn't need fresnels at all...

There's a much bigger issue - those fresnels in front of the panel would magnify the image and:

1) Make the throw extremely short.

2) Prevent the virtual image of the panel from fitting in the FOV of the triplet.

At least, that's what I think from my meagre knowledge of optics. Someone else can correct me if I'm wrong.

You can add a Fresnel or you can move your front Fresnel forward this will reduce the front fl and thus make the arc image smaller. For some one with the pro lens this is doable.

But Fresnels are not vary good lens so every mm forward you move the Fresnel the greater the distortion.

I have added Fresnels just like you have drawn and it made for vingeting of the edges of the image.

A negative Fresnel will work too but it will need to have a vary long fl or it will distort the image a lot.

A page magnifier from office max will work for this test.

A large anamorphic negative lens might work but If you are going to make one lens to try to correct a problem why not do two?

I'm skeptical as to how you could make a mold shaped accurately enough. The level of accuracy required for optics is extremely high and I think can only be achieved using sophisticated machinery.

But if you think you can do it, godspeed!

Thanks for the positive input

Making a mold from a master lens would be fairly high precision. If the finished lens disk had a good surface then the polish will not change the shape much. It is more about the designed and materials. If I handed most people a raw lens they could polish it with some instruction, and end up with a nice part. Even you.