| eebasist |
I found a perfect reflector for the project....its originally a 100W MH reflector designed for architechtural lighting....i got the whole thing for 35$ and bought a M59 highbay ballast for 30 today....i'll be showing you all the retrofit in a few days.
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| zardoz |
You and Undream have the same source of supply? He has one allmost identicle.
zardoz |
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| ap0the0sis |
wouldnt that reflector put out a goldish or yellowish light because of the color it has?
ap0 |
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| eebasist |
| a reflector doesnt "color the light" however a colored reflector is less efficient than a nice aluminized one. Undeam and I might have the same one...that would be funny wouldn't it? |
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| Property |
We can make our own custom reflectors VERY cheaply. EVERY single hardware store carries a fast drying super-strong concrete powder (meant for filling cracks in driveways, etc...) for $5 called "RockHard" (i've seen it in every single hardware store i've ever been in and i've cast stuff with it before). All you need to do is make a formwork (balsa wood) and pour a thin shell reflector. Then it can be painted (or film can be applied to it) with whatever paint you want.
One question though. I've heard on here that a reflective metal finish is better than using mirrors in your reflector. Why? |
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| eebasist |
Mirrors impart multiple reflections
1 for the glass
1 for the silver lining
=bad |
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| Property |
| what about front surface mirrors? |
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| Property |
| That's a nice reflector by the way...what is it some kind of compound parabolic-elliptic deal? And would you be willing to mail it to me so i can cast a copy of it with RockHard? j/k :p |
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| Property |
Hmmm... Ok found many many sources for High Heat Resistent chrome and aluminum finish paints...So I think my RockHard idea could be done....It would take a couple of days though: Making the form, pouring the thin shell, letting dry, painting etc...But any reflector shape could easily be made.
RockHard is very heat stable as well. Very little chance of shrinking/expanding/cracking due to heat |
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| mattboy2 |
| intereting concept, but you would lose much of the shape in all the gluing and what not, and thus lose all the light concentration. . . a good idea though if you can pull it off efficiently, or cant find a reflector.. im still searching :rolleyes: |
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| Property |
You wouldn't lose shape. Balsa wood is EXTREMELY flexible and you could back all the joints with an extra strip of balsa.
Balsa is just a suggestion though (the best suggestion IMO)...and you can use whatever you like for the forms...I've used just cardboard as forms before.
Also remember you can sand this stuff. |
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| mikekniner |
| I purchased Undreams reflector from him since he wasn't going to use it anyway. He's shipping it to me tommorow. Ill be using a 400 W MH in it, can't wait to try it out. Hopefully it will make my PJ brighter! |
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| mhelin |
| What's the point with the paraboilic reflectors anyway? I thought it was a bad thing to have a reflector other than spherical one which is still a point source, not a beam source like the parabolic reflector. Does it make the collimator fresnell (side) kinda useless? |
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| Property |
Depends....I just showed a parabolic reflector because it was easy to draw. But any reflector in any size can be made how I showed, for instance a spherical or elliptic reflector, or some kind of combinations.
I think also that someone could design an efficient lighting system around a parabolic reflector.... Maybe with some kind of baffle which let's only collimated rays go from the reflector to the focusing fresnel...This system would have potential to eliminate the center hot spot.... |
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| mikekniner |
Hey
Im playing around with undreams reflector. I keep getting a center hotspot though lol. How do I get rid of it? Any Ideas? |
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| Property |
| Without knowing what type of reflector it is it's a little hard to tell. From undream's posted pic it looks like it may be a parabolic reflector. The hot spot you get might be ok once you put a fresnel in front of it (Just be sure you put the bulb arc approximately at the focal point of the parabola). In any case you might get this problem with a parabolic reflector: |
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| Property |
| I thought of this idea to deal with the above problem..Note it cuts out alot of the "center" but if it's very little it may be ok...the second reflector is spherical and cuts out the "bad light rays": |
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| Property |
But if the reflector works fine and the only problem with your projector is that you get a bright hotspot in the center,
Then the most common fix i've seen on here is just dim down the center light by putting a piece of semi-transparent scotch tape somwhere, like in the middle of the lcd or the fresnel or the projection lens or the condensor lens or in front of the light (example pic of this below) or you could even paint the center part of your projection screen a slightly duller color than the rest. I saw one guy mention making a transparency at Kinko's with the center(in the shape of the hotspot) slightly shaded....It's basically just the concept blocking some of the intense hot spot light...you could probably even use the lens off a pair of sunglasses strategically placed to dim down some of this hot spot light: |
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| eebasist |
| what happens when you use 2 fresnels? And what type/size lens is a collminating lens |
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| mikekniner |
By the way I found out this relfector is elliptical.
Thanks for the info, any other ideas for an elliptical reflector? |
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| Property |
Most OHP's use two fresnels and the system is basically this (pic below):
So you can guess what problems may occur with 2 fresnels and different varieties of reflectors.
As far as other types of lenses i'm not so sure....I still need to do some more investigation of different types of lenses etc... |
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| Property |
| Elliptic reflectors are really interesting...I haven't had any SOLID ideas with elliptic reflectors but i'm sure there are some good ones...Basically this is the concept of an ellipse so, you can think up all kinds of ideas: |
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| Property |
So your reflector being "half" an ellipse will direct all light eminating from the bulb (located at focal point) and hitting the reflector surface, to the second "imaginary" focal point....if the imaginary focal point is at "infinity" then you have a parabolic reflector.
As far as ideas for this reflector...nothing solid yet....I was mainly looking at it for LOA fluorex lights, but nothing solid out of it. |
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| mikekniner |
| Ok, Thanks for all your help, I think im just going to stick with another reflector I have, it works and provides great results, ill put the elliptical one aside for a bit |
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| Property |
Ahhh...right...so that explains your hot spot....I guess. The scotch tape technique will probably end up being the best fix for the hot spot then......
But that's a big *** reflector....So your whole hot spot might cover your entire LCD screen so you might end up without a noticable hot spot...How big is your hot spot (?) and how far away from the wall is your reflector? |
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