Last night I got a wierd idea when I was laying in bed way light at night, unable to sleep. It was all I could do to not get up and test it right away.

If you move your lamp 1 inch closer then the focal length of the collimator, the projector still works. It may not be optimum lamp placement but it doesn't hurt the projection much. If you move the lamp 1 inch behind the focal length of the collimator, again not ideal but it still works.

What if they were both there at once?

With the small case of the t15, you can place a flat mirror pretty dang close to the arc. Like 3/8 from the back of it. This creates another virtual arc about 2 inches behind the first one. If you average it out, their positions by placing the mirror at the collimators focal point, you have two arcs, one about an inch too close, and one about an inch too far. But they worked before so it should work now. The only difference is they are both there.

I took out my pro reflector and mounted up a flat mirror just as I explained, and readjusted the bulbs location. I'm not going to make any official statements but it seemed brighter to me and more then a bit. But it was just an eye test and I don't trust myself with that. Anyways, the trouble with my experiment is the mirror can't withstand the punishment of a 400 watt halide when placed right up against it. I only let my projector run for 10 minutes at a time lest the mirror get too hot and shatter. But cracks are beginning to appear so I better find something else.

Anyways, I thought maybe someone who is as crazy as me and has a luxmeter might be willing to conduct an experiment. And see if the noticable improvement I saw was for real or just my imagination, But BE CAREFULL! The mirror could easily shatter! Keep the box closed and don't let it run too long! Oh and btw, if you have a pro lens set up this might not work as well, since the longer collector seems to magnify slight innacuracy of the bulb placement. :-/

Note, the improvement I saw was after I already installed the pro reflector. I got really excited when I saw the pro reflector, its so reflective! But oddly enough I saw almost no noticable improvement when I installed it. Maybe a 10% increase. I blame it on the arc. They clearly are hardly translucent when operating. I think thats whats good about this idea, most of the light is not being reflected back through the lamp arc so its not filtered out. Though the middle portion is. But thanks to the old inverse square law we have compensation for that.

Anyways, my tests were rushed since I only allowed the bulb to run for 10 minutes, so I didn't have much time to evaluate it. But it looked good in my oppinion. Real good.

I've been thinking about this idea for a while, just haven't gotten around to testing it. Well actually I'm having trouble finding a flat reflector to use that can withstand the heat.
You would think this would be a good idea... flat optics-flat reflector.. why not?! The avantage should be great since you're using the whole back side of the bulb and not trying to force rays back through the arc, also you'll be able to decrease the size of your box.
The only problem I see would be the glass envelope and possibly mogul, blocking some of the light causing uneven distribution, but that may be overcome by proper placement.
Click to view attachment

I think it would be brighter sure....but from what I can see you'd have the reflected arc being the one lighting the corners...resulting in a hotspot...But that's just my guess...

There is a possibility of it being much brighter in the center but I think there's no way to tell for sure until we put it to the test.
Does anybody have any recomendations on a reflector?

I believe for proof-of-concept tests any mirror will suffice provided you keep it very well cooled.

Edit: Sorry, I jumped the gun there. Thought you just wanted to test it again and not actually implement it in a projector. Small mirrors are so cheap though that you can do many tests even if they break. And they almost certainly won't shatter explosively. You'll just lose a few bucks to see the results for yourself if you really wanna try it and you'll be better off checking first and investing in a high-temperature mirror later if your results are satisfying.

How about one of the mirrors they use inside of overhead projectors?
They should be able to take a reasonable amount of heat.

SJ

A mirror is a reflector system with a gain of 1. It will work but will create two focal points. They have to be close together to work. At the triplet you will have a focus pattern just like you have on the other side.

Holy crap! For like three days straight no one said a word on this thread, I thought everyone thought it was a dumb idea and I felt like deleting this post and burrying my head in the sand. And I walk in today and boing! Six replies!

Anyways, yeah, AV is right, the arcs need to be way closer then that. With the t15 if you place a mirror right up against it, the virtual arc is a little under two inches behind the first (center to center).

We may be able to get closer with one of those double ended hqi's or the upcoming small arc lamp, however, the advantage of this system, I believe is that we are not reflecting light back through the arc as not to be filtered out. If we bring the second arc two close to the first, we might as well be using a spherical reflector. Take a look at this pic. If for instance we had a lamp with a mirror inserted inside the glass envelope, right up against the arc, most of the reflected light would have to go back through the arc so we'd be back where we started. There would be a ballance somewhere between where the arcs are too far apart and where they get in eachothers way. I think the t15's distance may be just about right but different distances should be tested. So lamp and mirror placement are tweeks that would need to be tested.

But let me tell you, the mirror I had was afixed to a piece of wood. Not only did the mirror crack but the wood behind it was charred to a briquette! That mirror is reflecting like 90% of the light so thats happening with radiating heat alone! Pretty scary.

I wonder if it would be better to have the mirror open on both sides. Maybe it cracked just because the front was so much hotter then the back.

What we really need is a flat mirror made from the same stuff as the pro reflector. Are those cold mirrors sold anywhere else?

Anyways, I don't know what kind of improvement we can expect, if any, I just thought it might be a good idea and worth posting about.

ya know i was walking through a surplus store in my area and i found a surplus projector light engine.

Its for a small slide projector, it had a ENX bulb and it used a dichoric mirror and a condensor lens..

The mirror was the same stuff that the pro reflector is made of but it was only like 2"x2"

You think a mirror that small would work for this?

They had like 5 units there for $20 a piece.. maybe i'll pick one up and play around..

Well if its the same stuff as the pro reflector it should hold up. If its perfectly flat I'd say its worth a shot if your willing.

Well....I don't know about anyone else....But I had to let the idea simmer in my head for a few days before I could give a meaningful response....Not to mention anyone is going to be hard pressed to try and get the idea of an elliptical reflector out of my mind...

Mikau, I believe the pro reflector is made of borosilicate glass (same type of glass that the bulbs outter jacket is made of)... there are different manufactures of borosilicate glass which market it as pyrex, borofloat, etc...

gs

ok i'll go buy one and salvage the mirror..

But what do i need to do to test this?

I currently have a punisher style projector so its a vertical.

I have the ushio s400dd short bulb and the ikea napkin holder reflector., Do i wanna remove the reflector and place this up against the bulbs bottom?

What do i need to do to my fresnels?

You don't have to do anything to your fresnels. But you will probably need to adjust your lamps location. I'm fortunate enough to have a lamp adjustment system. You need to move the lamp about one inch closer then the focal length of the collimator. So when you put the mirror in, the other arc will be an inch too far. But this averaging out may or may not be the best possible arrangement. Lots of tweaks should be tried.
And as I said, increasing the distance between the arcs a bit (by moving the mirror a bit farther away) may help as well. Like I said theres a ballance between where the acs become too far apart to focus, and too close where they get in eachothers way. But I do think the ushio/t15 bulbs give us just the right distance.

Though I warn you, I'm not sure if a slide projector bulb is as fierce as a 400 watt halide as far as heat is concerned.



I don't know what the heck its made of. I've never seen anything like it.

Ok.. it may take some time to do as i have to figure out a way to mount the mirror against the bulb.. and be able to adjust it..

My bulb can already be adjusted quite a bit so i should be able to play around with differnt distances.

Good. Yeah a vertical projector will make it a bit more tricky to adjust the mirror location.

Btw, if that mirror still is unable to withstand the heat, there must be some shiny flat stainless steel cooking pan of some sort at Ikea to test it with. Even though that won't work quite as well as a mirror.

I cant believe I read this post days after I throw away my broken mirror fragments.... they were large enough to reflect the whole arc. Sorry guys, I would test if I could.

Nick

Has anybody had a chance to try this out yet?

phife said he got a dichoric mirror and will be trying it out soon. I think he has a vertical projector and is working on building an adjustable mount for the mirror.

That's great! I think it's a very interesting experiment that needed to be done. Now the long wait for results.

phife said he bought two mirrors, and he was willing to sell me one. But I don't have a digital camera so I couldn't post comparison pics. But if you or someone else is interested, he'll probably be willing, ask him.

I can quite readily swap out my pro reflector for a flat mirror so - yeah - I'm game. I'll PM phife. Be nice to have a couple of setups to compare.

You could replace the mirror with another bulb altogether if this works.

Mark.

Then we'd be using twice the power and loosing twice the light ! I'm still not sure how adding a mirror would be better than adding a pro reflector ? ... the pro reflector I would think is going to give you better light direction than a flat mirror... as always, it would always be interesting to see the results.

gs

Pro reflector -> Lamp 1 -> lamp 2 -> First Fresnel.The pro reflector sends light back through the dull arc tube, wherease a mirror will spray it out mostly around the tube. You could get a similar effect by just moving the Pro reflector back a bit (you could even test this yay or nay with the model DAZZZLA and I put together) but just for fun I want to see this done.

Mark.

Since I've seen in the past people moving their arcs both toward AND away from the rear frezzy focal point to even out illumination my thinking has been that with a flat mirror you can kind of have an arc both closer and further from the rear frezzy at the same time.

Of course, in the end, it'll likely wind up not being any better than the current primo setups - but seeing these experiments done is always entertaining and informative.

This is a very creative and interesting idea and I'm looking forward to the results.

But I have to state that there's no way that the arc itself obscures light. It's a plasma, it's the source of the light - it doesn't have the physical properties to absorb the light.

Clearing the jacket could be a measurable win, though. And using the tolerance of the rear fresnel to pump more light through it is a really cool idea.

Perhaps its not the plasma but clearly something about the arc is doing it. A 90% efficient reflector produces about 50% more light, a 60% efficient ikea reflector produces about 25% more light. If the arc were not filtering out light we should be getting double the light from the pro reflector, but clearly we don't. Plasma or not, something in the arc is eating up light.

Another idea I had, most of the lamps we use have an arc thats more then twice as long as its diameter. On my triplet I get a narrow line of light thats wider then the triplet, but very thin vertically. If we had arcs that had a larger diameter and weren't as long we'd be able to use a lot more light. Though I it may be necessary for metal halide arcs to be tubular for them to work properly. Even so, perhaps two paralell arcs, real close together would do the trick. But that would need to be custom designed.