Go Back   Home > Forums > General Interest > Everything Else > The Moving Image > DIY Projectors

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 27th November 2004, 07:06 PM   #11
diyAudio Member
 
Join Date: May 2004
Location: CA
Oh no! I thought a cold mirror transmitted IR and UV...all this time I've had my projector set up with only the cold mirror as my defense against heat and UV...what kind of glass should I use (or what could be found at homedepot ) that can get rid of the UV? And should I just put it right before the lower fresnel?
  Reply With Quote
Old 27th November 2004, 07:19 PM   #12
diyAudio Member
 
ace3000_1's Avatar
 
Join Date: Mar 2003
Location: spain
Send a message via Yahoo to ace3000_1
Quote:
Not to sound snappy or anything,
LOL np buddy.

The focal i was talking about was the rear frensels focal length, unless its over 400mm long you cant get 2 mirrors folding the light behind the lcd, and this is only with a 7inch lcd im talking about, the bigger the lcd the bigger the mirror will have to be on that design.

The best thing to do is to draw up a full size plan. If you know what optics you are using (focal lengths) its all go to the plan then build with only minimal final ajustment. Another way to go about things is see what size you want as an end product first, then see if those optics are available to maintain that size, if its not possible either change the optics or the design to suit.

Trev
__________________
"Every technique can be used in a great many ways, but mastering it, thats what realy counts."
  Reply With Quote
Old 27th November 2004, 07:33 PM   #13
Hudson is offline Hudson  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Virginia
Froz

Need a UV filter? Go hit home depot and look for UV filtering lextan, it will have a green film on one side, pretty cheap. i think the green film side is the side you want your light coming in from, not sure. *pause for dramatics..* search the forum.. the stuff is cheap cheap tho, you can buy quite a bit of it for just a few bucks.

As for how much of a dent it makes in your optics, i have no idea. yet. but thats what i plan to use. There is UV glass, too. since UV is easy to filter vs stuff like IR, UV filtering materials are /way/ cheapr than hot and cold mirrors. everything and its dog filters UV, car windows, sunglasses, inlaws, etc, the material is so common, its almost scary. I wish the same were true for IR related stuff, it would make life alot easier about now.

Ace
Thats roughly what i'm doing. The 3d images you'v seen are, at the moment, just winged. Once we nail down at least a design theory thats sound and workable, we plan to go back, make it to 1:1 scale with real measurements (in 3d anyways, but measurements that are taken from real life measurements) and then we start crunching the focal math to see what needs to change.

Thats the cool thing about this - i can, in theory, build thousands of projector variations, and not really spend a dime. Once i find the 'happy spot', i can take all the numbers and measurements, know exactly what i need to buy and how much, and then do the nike. (just do it)

Well, thats the plan, anyways. We start crunching focal math later today or tomarrow, so..lets hope it doesnt throw /too/ much to peices.. i'm still iffy on just how to calculate all this focal stuff. math, sadly, isnt my best feild. :P but i'v been finding some handy online lens calculators that make things a little easier.
__________________
I will not rest untill I can frag, watch movies, and display pr0n at at /least/ 150"
  Reply With Quote
Old 27th November 2004, 10:34 PM   #14
Hudson is offline Hudson  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Virginia
This is why we dont use the back button, hudson. (edit out double post)
__________________
I will not rest untill I can frag, watch movies, and display pr0n at at /least/ 150"
  Reply With Quote
Old 27th November 2004, 10:58 PM   #15
diyAudio Member
 
Guy Grotke's Avatar
 
Join Date: Sep 2004
Location: Vista, CA
Default cold mirror in light path

The real problem Trev mentioned is that your lamp has to be at the focal point of your lower fresnel. With a 15" LCD that means the path is pretty wide, unless you use an extra-long fl fresnel. Look at the drawing I have attached. This is the light path between a 24 mm arc and a 15" 220 mm fl fresnel. I tried to see where I could fit a cold mirror (blue line), to reflect the light (red lines). That is a very large cold mirror!

If you use a longer focal length fresnel, then the cone is not so fat. So it is easier to use a smaller cold mirror.
Attached Images
File Type: jpg coldpath.jpg (3.2 KB, 109 views)
  Reply With Quote
Old 28th November 2004, 01:56 AM   #16
diyAudio Member
 
Guy Grotke's Avatar
 
Join Date: Sep 2004
Location: Vista, CA
Default no UV filter?

frozenbum_87:

You actually DO have a UV filter, because an acrylic fresnel will filter out quite a bit of the UV. Maybe you have both fresnels below the LCD, so that would filter out even more UV. Ordinary window glass is not very good at removing UV. That is why they sell window film you can apply to prevent your carpet and furniture from fading. You can pay quite a bit for special glass that does filter more UV. Or just go to Home Depot and get a piece of Lexan XL for a few bucks. That is a great UV filter, and you can use it to support your lower fresnel so it doesn't sag and screw up the focal point. (It has much better heat resistance than acrylic.)

As for your cold mirror's transmission/reflection spectra, you might have a visible light bandpass mirror that does let some UV through along with most of the IR. Probably not. Lowpass or highpass filters are simpler to make. Your cold mirror probably does reflect most of the IR.

You can test a dicroic filter to see if it reflects or passes IR using a remote control and a TV camera. A TV camera will "see" a standard IR remote control as a brilliant point source. If you interpose a good IR filter, then it should be much dimmer.

You can test a UV filter using a blacklight and something fluorescent. (Maybe you have an old poster, some paint, a T shirt?) If it glows brightly under the blacklight, see what happens when you interpose the UV filter.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Input & Feedback filters lhwidget Chip Amps 11 27th June 2009 09:16 PM
WANTED>>>Overhead projector or projector!!! phaze5 Swap Meet 1 12th June 2003 04:24 AM
Feedback wanted on PSU design Ralph Tubes / Valves 16 26th September 2002 01:29 PM


New To Site? Need Help?

All times are GMT. The time now is 03:08 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2