Ye olde cardboarde and lense projecte (r) - diyAudio
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Old 10th December 2004, 09:44 AM   #1
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Join Date: Dec 2004
Location: Punxsutawney, PA (Yes, really)
Talking Ye olde cardboarde and lense projecte (r)

I finally decided to try several different, for lack of better term, technologies, starting with the oft advertised and much despised fresnel lens in a cardboard box. There doesn't seem to be any recent discussion of the topic here... likely for good reason... but that's what is going to make this fun for me. I don't expect IMAX, so please, don't bother trying to talk me out of it.

My first 5 minute experiment with not-quite-right sized boxes (held up by the weight of the TV on the box flap) and my lens just brought home from Staples produced a brighter image than I had expected. Not bright, just not as bad as the many forums I have lurked in led me to expect. Focus was of course lousy, and not even consistently so, and the inversion and inability to control the projected size short of moving the TV (easier than the wall at this stage) makes this first hasty attempt score poorly. Aside from the mediocre brightness, it was just as bad as I expected, but not quite as bad as I was prepared for.

I'll try to take the best of the methods available online, and any constructive comments from those of you that have done this (HINTHINT), and make something reasonably approaching watchable. My progress, if any, will be documented here for your amusement and mine.

Future builds will include a panel/OHP setup, the rather impressive game controller/slide projector setup, and eventually something approaching the quality of commercial projectors. By the time I get all of that done OLED projectors should be affordable to us all!
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Old 11th December 2004, 12:37 AM   #2
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Join Date: Dec 2004
Location: Punxsutawney, PA (Yes, really)
Ahh, the things I have learned already...

A little tweaking of my somewhat disposable TV (19", cost $5, is pre-remote with actual dial tuning, but doesn't turn green when inverted) or perhaps replacement with a smaller flat screen unit, an upgrade to a meniscus lens (131mm diameter or above, around 500mm fl, roughly $20), a more carefully built box, and a high gain screen should get me up to par with the commercial projectors from just a few (in old man terms, anyway) years back.

In the mean time, relocating the setup to a position where the projected image fits on just the wall (in other words, moved to the middle of the room... the longer fl of the lens listed above will fix that) improved the brightness and focus somewhat, and sealing the box better seems to have helped, but only slightly. I suspect that factor will be more important when there is more ambient light in the room. I'll post a link to a few pics soon, in case anyone actually cares.

By the time I get this done I should be ready for the next level of technology, assuming eBay treats me well.
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Old 11th December 2004, 04:27 AM   #3
ancorp is offline ancorp  Canada
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Join Date: Jun 2004
Location: Vaughan, Ontario (near Toronto)
hey hey! go to www.diyprojectiontv.com, read some stuff there, and ofcource join the forum (chat group) listed there, you can get lots of help...

A better than a fresnel lens is necissary. I moved on to triplet lenses now (my current lens is 175mm in diameter). The focus is quite decent on a CURVED tv set, and has about double the fresnel brightness...
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Old 11th December 2004, 04:57 AM   #4
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Join Date: Dec 2004
Location: Punxsutawney, PA (Yes, really)
Yup yup... been there a lot the past couple of days. I joined the msn group earlier today so I could get to all of the "members only" stuff. I was gonna post some pics there of phase one tonight, but I kind of forgot to charge my camera batteries.

The lens I mention in my post above was the type most discussed in the threads I've read through so far. I'll pic something up soon, but right now I'm holding my projector cash out in hopes of getting something useable on eBay for my actual theater setup. BTW, how much did that lens set you back?

Based on some of the more recent design discussions, specifically the recommendation to not use a cone shaped enclosure, I'm going to try going with a slightly larger box than my screen would suggest. Of course, much of this decision is based on the fact that I found a top to a banana box with a hole in it almost perfect for my fresnel LOL. I'll try to avoid the urge (for now) to line the inside with black shag, but I definitely want to figure out a good way to trap any stray light that might otherwise bounce onto the lens and cause fuzziness.

Now if I can just get the brightness controls to work on my dinosaur of a TV....
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Old 11th December 2004, 06:12 AM   #5
ancorp is offline ancorp  Canada
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Join Date: Jun 2004
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that lens set me back about $30-40 US. I got it as part of a trade. Great deal if you ask me!
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Old 12th December 2004, 03:25 AM   #6
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Join Date: Dec 2004
Location: Punxsutawney, PA (Yes, really)
Here are a few pics of my very crude stage one setup. Some of you will smile, some of you will laugh, and I suspect that a few of you will be tempted to actually hunt me down just to slap me.

Never fear, I'll have this thing up to drive-in theater quality in no time!

The pics.
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