Bout time I have a go at this projector building stuff!!!

[HiLLBiLLY]

NottaClu...for someone with that nick you have done a wonderful job, soon as that LCD is cooled a little and some minoir tweaking im sure you will be a very happy and proud owner of a kick a s s PJ and no doubt have a few envious friends *wink* ......well done :-)

"I want to see that again, but this time on your projector." So my biggest critic (and my best supporter) thinks my PJ is good enough to watch...

Ah Guy... bet that made you feel nearly as good as when you first saw an image produced on your first DIY PJ didn't mate :-) Would surely have been one proud moment in the Grotke household that evening :-)

[NottaClu]

does the light from a hot mirror go stright through it, or does it bank the light like a regular mirror. If it just refelcts the heat....and lets the light through....where is a good place to buy one of these???

[Guy Grotke]

Hot mirror reflects infrared light (just like a mirror) but transmits visible light (just like glass). Most of the optical supply places sell them, like Rolyn and Edmunds, but they are pretty expensive.

I know of two sellers of surplus hot mirror at reasonable prices:

surplusshed.com has 50 mm by 55 mm squares that don't seem to work very well, with my simple "halogen lamp & burnt finger test".

diybuildergroup.com has 50 mm by 50 mm squares that do seem to work very well in the simple test, and in my projector. I built an aluminum frame to hold four of them, to give me a 100 mm by 100 mm heat filter. I put it right up against my lamp.

diyprojectorcompany.com has a similar item for sale that is a heat reflective plastic window film mounted on glass. This would have to go further from the lamp than real glass hot mirror. Like maybe as a fresnel support 220 mm from the lamp.

[NottaClu]

here is another question....

My condesor lens is about 1 inch from the edge of the bulb...it is the 60mm 110fl condensor from diylabs. My first fresnel is 220mm away from the arc of the bulb. Is one inch away from the bulb too far away....or should I move it closer to get a brighter image...tell me what you guys think....

thanks

drew

[HiLLBiLLY]

NottaClu

I run mine inbetween 3-5mm from the lamp...maybe give that ago matey just make sure the condenser lens has adequate cooling and mounted to allow for a little expansion if it decides it wants to move a 'lil bit buddy ;-) If you don't you may get the same result as a fellow DIY has gotten (one more than one occasion i believe during testing the limits of individual lenses)

[Moose]

Originally posted by NottaClu
here is another question....

My condesor lens is about 1 inch from the edge of the bulb...it is the 60mm 110fl condensor from diylabs. My first fresnel is 220mm away from the arc of the bulb. Is one inch away from the bulb too far away....or should I move it closer to get a brighter image...tell me what you guys think....

thanks

drew

Hey Drew

Heres a theoretical sketch of where your condensor and arc should be. You should move your arc in a bit since you are using a condensor. Just use this as a guide as its not really accurate to .01mm (probably more like +/- 2mm, but it should make things a bit brighter.

Mark
Fresnel setup

[NottaClu]

first fresnel should be at its focal from the bulb correct...no matter if you are using a condensor or not??? I could be wrong but thats how I thought it was. If this is the case...should I just move the condensor back further......I guess I just want to know an easy way to get maximum light over the lcd....for brightness purposes...

thanks

drew

[TaskMaster]

Originally posted by Guy Grotke
I built an aluminum frame to hold four of them, to give me a 100 mm by 100 mm heat filter. I put it right up against my lamp.

Do you have a pic of that by any chance? I was just wonderiong how you support the four pieces.

Thanks.

[Moose]

Originally posted by NottaClu
first fresnel should be at its focal from the bulb correct...no matter if you are using a condensor or not??? I could be wrong but thats how I thought it was. If this is the case...should I just move the condensor back further......I guess I just want to know an easy way to get maximum light over the lcd....for brightness purposes...

thanks

drew

By adding a condensor lens you change or bend the light as it goes through the lens. So the condensor lens makes the arc appear to be at the focal length of the fresnel, even though it is not. Take a look at the sketch I posted earlier. The outside lines, are the most extreme rays that make it to the the fresnel. If you follow the one from the arc w/ condensor location, it gets bent by the condensor lens, and becomes the new ray going towards the fresnel, but from the point of view of the fresnel lens, the light appears to be coming from the point at its focal length.

The whole point of the condensor is to allow more of the light from the bulb to end up at the fresnel, and it does this by bending the light that would normally miss the fresnel in towards it. So again looking at the sketch, the interior angle of the triangle for the point without the condensor is 23.4 degrees, so without a reflector, 47/360 = 13% of light from the arc hits the fresnel. The angle from the condensor arc position is 37.5 degrees, so 75/360 = 21% of light hits fresnel.

Hope this helps.

[NottaClu]

thanks man appriciate it

drew