In the top right hand corner and the bottom left hand corner of my projection there is a green and pink patch of color. It looks like it is either coming from the fresnel lenes or the lamp itself. I am using a 250W doubled ended with a condensor lenes and spherical mirror.

Any ideas?

Well my guess is that its the mirror ...... mirrors can play a role in some light spectrum projections ....

That is just my guess, cause I have no experience in using mirrors, but most around here have said that they WOUDLNT make good reflectors ...... this might be why!!

I will try removing the mirror but I purchased the mirror from an optical suppliers. This mirrror is designed tobe placed behind a lamp. So I doubt it is that?

That doesnt mean its idea for a projector reflector .....

The goal of your basic reflector is to just simple reflect some of the light forward, however with a projector you want a point source of light ..... for a proper projector reflector it will have a focal point, the not only reflects the light ... but reflects it back onto the arc tube of the lamp ...... so you end up with a result that is as close as phyically possible with a point source of light .....

If your reflector doesnt focus the light back onto the arc tube of the lamp, then there could possibly be an off axis light array, while the fresnels arent supposed to pass any of this off axis light through the LCD, it is possible if the light is way off axis ....

I urge you to read up on our threads over reflection .... you can buy a reflector that many are using now, for only $4 .....

Yes I have read many topics and none of them cover this topic. The spherical lens is perfect and the arc is dead on the focal point. This mirror is designed exactly for projectors, hence it being spherical. My components are very accuratly made on a mill. In fact I have made all my components in a workshop and are very well made. I also design luminaires for a living and know a great deal about optics!

Yet this problem is difficult. I think it has something todo with a prism effect on the fresnel lens edges. None of these projectors have a perfect point source btw so there will always be off axis light traveling through the fresnel.

Olly, it sounds like you've got a nice setup. Hopefully you'll do a plog soon so we can see your setup. I'm definately no optics expert but it sounds like a fresnel aberration to me or possibly the triplet. Are you using the Lumenlab triplet? I would think that you need to go through a process of elimination here.

Intuitively I would first suspect the field fresnel's position and flatness. I would try moving the field fresnel toward the triplet. I have seen rainbows in Lexan if you are using that (not my favorite material as a heat shield). Does your spillage look even and if it doesn't, do you think that this might contribute to aberration in the triplet? If you can get a look at the panel with the lamp on and can you see the problem there? At least this might tell you which half of the projector is causing the problem. Have you tried moving the lamp in relation to the collumating fresnel? I kind of doubt that the lamp is responsible unless somehow the glass envelope is causing a prismatic effect. I'm just throwing out some ideas here with the hope I might hit on something. That's all I've got. Good Luck.

So when are you going to design/manufacture us an ellipsoidal reflector?

Sounds like coronal diffraction mixed with leakage or spillage. Double check for any leakage or spillage. Check the alignment of all your optics especially the reflector and precondensor. I suggest following scubasteve's advice. A reflector precondensor setup is very tricky. Alignment must be absolutely perfect and you must have the right optics. You can't just throw anything in there without knowing absolutely sure it'll work. Even without the reflector the precondensor alone can cause major problems. Kinda sounds like it may be too far from the lamp also. Try to run without both. Are you still using the floor standing with external tracking mirror setup? If so, is it a front surface mirror? Also, what size LCD are you using? You'll need precondensor focal lengths for the following: 25mm for 8", 15mm for 15", and 14mm for 17" if your using a 220mm condensor fresnel.

Thanks for all the advice. It is definitely not the triplet or the FS mirror but something further down the line.

Once I have a digi camera I will post the results. Just for your information I am building it into a coffee table. Using my experience with lamps I have managed to overrun a 250w discharge lamp using a 70W ballast run in parallel with a 250W. I am forcing air via a tunnel over the lamp to keep it very cool. This means I can have a very bright small arc which is great for projectors. I just hope the lamps lasts but only time will tell. BTW you can only do this with the traditional iron wound ballasts or chokes whatever you want to call them.

Yeah, I'd like to see it. Sounds interesting.

Another mad scientist! If it can be overdriven I've probably done it. RF, CRT's, fluorescents, HID, computers, engines, motors. I could go on and on. Just make sure you keep yourself safe. There isn't enough of us to go around.
BTW that'd be one massive choke.

Oh god, what I would have payed to have someone around that was experienced in lamp-ballast use when I started going on this 1kw lamp tangent...

I await your screenshots

double E major here, and I would like more details on this ........ I believe in the little more light, unfortunatly there is a large gap between the 400W bulbs we use and the 600W bulbs ive seen ..... I saw a 450W MH bulb once, but it was in too big a package, and wasnt worth the increase. I wouldnt mind over-driving a bulb a little, even if it cut its life in half .....

A member here did that once, buy adding caps (Without any theortecial calculation I believe) and eventually blew something up to an unsafe standard ....... but from what you mentioned your method is safe .....

You said you have a 70W in parrallel with a 250W ..... is there any cases of impedance sinking back into one of the other transformers? Obviously current and voltage sources can be added, I would just be worried about a parrallel impedance effect, making the effective circuit resistance a little less than the smaller impedance ....

WARNING.....I never said anything is safe so please be careful. I have been told by a metal halide lamp designer that these lamps can be overdriven by 10%. That is 10% of the lamp current.

When you put a 35W in parallel with a 250W ballast the lamp is overdriven by about 10%. I decided that was not bright enough so I put a 70W in parallel instead. THIS IS WAY TOO MUCH FOR THE LAMP.

My enclosure around the lamp is made of steel and toughened glass and is air cooled individually with a 120mm high flow fan. In theory this should cool the lamp enough to prevent the outer and inner envelope from melthing but I have taken no tempeature measurements yet. Also the temp measurements could be invalid because there is a insulting vacuum between the two tubes and therefore the inner tube could still be getting too hot.

The inner envelope could melt then explode!!!!

I have found that with proper optics i.e. condensor lenes and glass spherical mirror, there is no difference in light output between a 250 and 400w doubled ended on the screen. This has been measured with lux meter. The arc sizes are 28mm and 36 mm respectively. The arc size is not the distance between the electrodes but the length of the arc. All arcs are very curved. So there is definately a relationship between the arc size and throughput in the lenes array.

Also, the lower the color temperature the smaller the arc size, that one I only found out the other day!Warm white lamps have a much smaller arc that neutral and daylight lamps.

I also have a proper eillipsodial reflector from a fibre optic light box. I have tried to get an even light spread with this reflector but have had no luck. It seems to produce a black spot with a few outer rings. Very difficult to align! I have not tried it with a condensor lens yet. I think you have to have a perfectly smooth reflector surface which you can only achieve with glass and vapour depoistion. Spun metal is just too rough!

Thats all for now I will be doing temperature measurements next week.

See ya