Film-Tech Forum ARCHIVE: Fresnel Lens Project

This is topic Fresnel Lens Project in forum Film-Yak at Film-Tech Forum ARCHIVE.

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Posted by Peter Berrett (Member # 672) on 06-06-2003, 10:40 PM:

Hi all

Like me you have probably stumbled across various web sites promising to turn your television into a big screen projector for comparitively modest cost.

Like many web sites of similar ilk (ie such as those promising to turn make certain parts of your body much larger in a short time [Smile]

) I have tended to dismiss these claims as excessive and not worth pursuing however after looking at another of these web sites I thought it worth to raise the topic here and seek some comment on whether these things actually work or not, and if so to what extent.

Let's start with one such web site

http://bigscreentv.20m.com/photo.html

Note that this project is yet another use of Duct Tape! Duct tape and cover. Duct tape and cover! [Smile]

Ok by now you will have worked out that the project uses a fresnel lens to take the light coming out of the tv screen and project it onto a wall. Sounds good in theory...

Ok now to my questions.

1. Has anyone here actually built one of these things?

2. Do they work?

3. Is the projected image bright and luminous?

4. Will it burn out the phosphorous on the tv faster than usual ie do you need to really crank up the brightness?

5. Does enlarging the image in this way result in the horizontal lines across the screen becoming more visible ie does the image
as viewed suffer as a result of being enlarged so much?

I have my doubts about whether this would work or not. I mean if it did, who would bother buying a digital projector?

Thoughts please

Also in a similar vein I have come across a web site devoted to building your own LCD Projector at minimal cost. This looks seriously interesting. I'd be interested to hear reader's comments.

http://www.louisville.edu/~wchall01/diyprojector/howto.htm#method1

Here's the results

http://www.louisville.edu/~wchall01/diyprojector/pictures.htm

It makes me wonder if there might be some way of interfacing a LCD panel to my Eiki 16mm projector. It might give a better image.

Thanks Peter

[ 06-07-2003, 12:47 AM: Message edited by: Peter Berrett ]

Posted by John Spooner (Member # 1565) on 06-07-2003, 02:07 PM:

Dear Peter.
Trust you and the fluffy dog are well, the 3 dachshunds send their regards.
I would be of the opinion that using a standard cathode ray tube type tv would not give sufficient screen brightness for satisfactory viewing, also the lens used would not be corrected, giving bad chromatic and spherical abberations. This in addition to magnifying the scan lines would result in a poor and distorted resultant image.Also the covering power of the lens would be insufficient and severe vignetting would occur, analogous to using a 16mm projector lens on a 35mm projector.
I will stick with my Sharpvision lcd projector.
My best regards to you and your family.
John Spooner. Adelaide.

Posted by Randy Stankey (Member # 64) on 06-07-2003, 02:30 PM:

I dunno'... If you like to tinker and you want to try a "Home Science Project" and you have the $$ then I don't see any reason why not. Just don't expect to get the same results as if you actually went out and bought the real thing.

I like to tinker with stuff, sometimes, and I often lose sight of the fact that it's often cheaper and easier to go out and BUY the thing you need instead of trying to build the thing from scratch.

We have an old charcoal grill out in the garage. It's missing some parts. It needs a grill rack to hold the cast iron grills in place and it needs an ash pan and the fire door is missing. I figured I could get some sheet metal and fabricate the parts in the workshop. Then I went to the hardware store to look for the stuff I needed. While I was there I looked at the charcoal grills they had on display. For $10 more than the price of the materials I wanted to buy I could get a brand new Weber grill!

I figured my time and trouble was worth the $10 so I came home with the Weber instead. My wife was a bit puzzled when I came home with a new grill instead of fixing up the old one but she was happier to be cooking on a nice, clean, new one instead of the slightly rusty old one. The $10 was worth it to her, too!

On the other hand, I downloaded the instructions to make a "Can-Tenna" for the base station on my wireless computer network and I almost doubled the range I can get out of it! It cost me about $20 in parts from Radio Shack! I had a fun time doing it too!

The moral of the story is: If you just want to do it for the sake of tinkering go ahead. If you think you're going to get something for nothing, you're probably going to be disappointed.

Posted by Peter Berrett (Member # 672) on 06-08-2003, 12:22 AM:

After further consideration I think it a fair bet that the fresnel lens applied to the tv set would give substandard results due to low luminosity.

However the lcd panel used with an overhead projector look ok. The major limitation appears to be the fact that the lcd panels are for the most part 640x480 vga. Furthermore I have been told that the LCD screens quite often only use 6 bits for the red green blue therefore you don't get 24bit, 16 million colors..what you get is 256000 dithered.

Still the proof is in the pudding. One of the guys who has such a setup is located in Melbourne. I will email him and see if I can drop by and have a look at his setup in action.

cheers Peter