Is it possible to use 2 lights for a more even result...has it been tried..apart from the cost what would be the issues ?

For instance 2 x 150watts or perhaps 2 x 250watts...

All are invited to blow this idea apart ....!!

The idea has been advanced but to my knowledge never tried.

You can check out this thread for one.

The idea's been mentioned elsewhere but the one above was put forth by me so I knew where to find it quickly.

Durachko

Thankyou, I read your post and idea..Im surprised no one has tried it.

I was thinking more of 2 lights in parallel possibly each light source having it's own rear fresnel,

So nobody has tried something like this to improve brightness/edge 2 edge brightness....?

Here's another one.

http://www.lumenlab.com/forums/index.php?showtopic=8219

Wow! I never saw that one before paladin.

I had an idea floating around in my head, it might work, I'll post what it would look like,

Here we go!

I drew it in five minutes, and its not exactly too scale.

Someday I may try to test a fix I that I thought of for the seam in the Fresnel. All you have to do is use a straight piece of metal to join them. This will cast a straight line so the line can be made to disappear.

I guess I should give it a bump

Arizona,

I bow my hat after reading Paladin's pointer to your original thread...(apologies for missing it !)
You were well advanced in your ideas.

Let's hope these theories get to be tried in an existing setup to compare results.
I dont know how many times I have read about peoples biggest gripe with DIY Projection...being Overall Brightness and especially Edge to Edge Brightness.

Your ideas or variations of like Litherish, Durachko's Im sure will fix the issue.

The dual Fresnels idea works fine the only reason I didn't do more with it is a single larger lamp was simpler and just as bright.


This idea does cut the Fresnel in half which will cut your brightness in half too. If you add a larger condenser lens to reshape the light cone to fit the Fresnel this makes the arc image larger yet. So in that respect it is no brighter than one lamp.

Arizona,
Bugger just for a moment it seemed to me these ideas would have been the go...

When you say that you will half the brightness can you elaborate for me and maybe for other optically challenged members.

I kept thinking of using 2 seperate fresnels cut to size not one 'cut in half' are we thinking the same ?

BTW Thanks for proving that a bigger light can be used to give us the image brightness.!

The Twin Fresnel setup is two Fresnels cut just like normal Center is the center of the Fresnel. If you wanted to you could off set the center slightly to move the hot spot more to the middle. They are placed side by side. I was trying to seam them so you can’t see the seam but this is unnecessary. You have two light systems that must blend at the front Fresnel so what you need is for the left side Fresnel to stop making light right where the right Fresnel starts to make light. The way to do this is to use a straight piece of metal at the seam to hold the Fresnels and to make a dark line to fill in by moving the lamps to create overlap.

By using two Fresnels instead of one big one each will be half the size so it will only collect half the light. The main advantage is the evenness will be much better because the difference in brightness from the center of the Fresnel to the outside is much less and so will be the angle that the light hits the Fresnel.

There is a power law called the inverse square law this applies here and is why this system will be brighter. As you move away from a lamp the light does not get dimmer in a liner way is the square of the distance so the light 80mm to each side of the Fresnel is a lot dimmer. This effect is cut in half by using two Fresnels but the gain will be greater than just the increase in lamp watts.

I still believe a two Fresnel collector will be more than 25% brighter with two lamps. You could use two shorter fl Fresnels and not have the problem of dim corners. Or a dual condenser lens system would be fine and brighter.

But there are some real drawbacks. Your lamps must mach in color and brightness. This shouldn’t be too bad and a 1uf cap to adjust the ballast might help.

You will now have two hot spots no one knows if this will look worst than having one hot spot in the middle.

Reading the frankenfresnel polg should help some.

Arizona,

Thanks for the explanation which Ive read and reread.
It does still seem that the Frankenfresnel idea is worth testing in a complete setup,as you say seeing if 2 hotspots look better than one and also seeing if the lamps can colour match close enough not to notice.

Im still in the process of sourcing parts so cant try this yet but will if I end up not happy with the brightness of the finished projector.

As for Lamps to use, that is a difficult one for me Im not sure yet ...still which lamps could be 'best' for use in a frankenfresnel design, for me cheaper is better especially when x 2.

It does seem to me that DIY projectors are a beast of evolution and this takes time, Im in no rush but it
is nice to be ready and setup to try a twin light source direction to go in or a bigger lamp solution if Im not happy with my single source result.

Maybe I should buy some cheap page magnifying fresnels for testing ?!
Question: You said to possibly use shorter FL fresnel..what FL were you thinking ?

TIA

This link says a lot about the light system

http://www.lumenlab.com/forums/index.php?showtopic=9126&st=0

Mainly the first page and the last three pages.

The only thing that has changed is the large lamp shells stop you from using a reflector so a condenser system is better for larger lamps.

Basicly the smaler the lamp arc the more magnafiction you can add this makes the system more efficent but it may not be brighter than a long arc lamp. Sim has a good thread on condenser lene...... skip the math and use dazzzla pre- condenser worksheat.

What about something like this "its rough as hell but i threw it together in minutes" 2 lightsources off the sides of the projector pointing inwards at an angle focusing on one Fs mirror and a condenser down the tunnel to focus the light a bit. drawing is nowhere near scale and ommited everything but the light sources from the projector for speed of drafting. wouldnt that take 2 light sources and combine them into one single light path? hell if that works you could even go 3d and have 2, 4, 6, 8, etc... smaller wattage and heat lightsources collimnating at one point. Just a theory shoot it down at will

Edit: maybe a parabolic mirror instead of a flat mirror?

I played with a homogenizing light tunnel and ellipsoidal reflector one time and thought of a 2 lamp system where the two archs would be "mixed" together with a dual tunnel of tapered mirrors like your diagram. After cutting a single light tunnel by hand, I don't know if I would have the patience to cut an elaborate design and construct it somehow. I still believe a homogenizing system would work with the right calculations and construction. I just don't have the time or money to play with it.

hell times all ive got.. money well some but you know economy and all that. i thought about throwing one of these together using some cheap cfl bulbs just to see if it worked but i dont have a luxometer so if i do it will be an eye gauge kinda deal.

i think i figured out a way to "test" this design to get the angles right. Gonna build a proto out of 1/4" paneling flat with a hinge in the middle shaped as to the diagram above. will place a small makeup mirror at the converging point and stick 2 laser pointers on the arms. by putting a small object on the area the condenser lense would eventually stay i think i could tune it. hmmm now this has got me thinking.. 2-4 small 70w-100w mh lamps in one projector. "drool" even though its not in anyway gonna be incorporated into my current build i think it would be a fun proof of concept weekend build to throw a couple of narrow beam lights on it once i get the angles down

With a pre con at the focal point, this would allow for an entire ring of bulbs. Ooooor, I have absolutely no idea what I'm talking about. Either way, I'd like to hear the physics behind why it does not work. Thanks.