Cold Ellipsoidal Reflector and 15" LCD


2003-01-01 11:36 pm
Can anymore comment on the performance of cold ellipsoidal reflectors and 15" LCDs?

I am contemplating a 15" projector setup. The components proposed for the setup consists of the following:

Benq 567s-v2 15" LCD

Philips MasterColor CDM150/T6/942 bulb

Edmunds 97mm dia cold ellipsoidal reflector

Aromat M15012CK-3EU-F electronic ballast
Lumenlab 1005 S15 lens kit

The CDM150 spec. sheet claims mean lumens at approximately 10,160.

Will the combination of CDM150 lumen output and the cold ellipsoidal reflector provide sufficient illumination through a 15" LCD?

lamp & reflector

That lamp should work very well in the elliptical reflector you referenced. (It would be a bit better if the color temp was in the 5000 - 6000 K range, but 4000 will still work.)

The challenge will be to find a fresnel that matches the diverging cone of light that will come from the second focal point of the reflector. You should try making a full scale drawing, since you have the reflector dimensions. The extremes of the light cone are rays that bounce from the reflector very near the edge, and then go through the second focal point. If you extend those upper and lower edge rays out so they are 15" apart vertically, that will show you the distance for a 15" diagonal fresnel. Then you can measure the distance from the fresnel back to the second focal point. That will be the ideal focal length for the condensor fresnel.

I tried this drawing exercise for both the Edmund's elliptical reflectors, and it looked like they were not very good matches to available fresnels for a 15" LCD. You may be able to make up for a mismatch with the second fresnel, but an elliptical reflector design has fewer distances you can adjust, than a spherical reflector design with a pre-condensor lens.

Hello. I want to use also an effective reflector for the 15,4"-wuxga-tft.
I can buy this Reflectors here in Germany, but this ist for me to small.
I will use a reflector with ~40cm for the whole panel (125% from the panel).
There are this "large parabolic reflectors":

But this is a simple aluminium mirror whitout the "Increase System Efficiency" :bawling: .

This good Reflector with 18"would be good.

Where can I find a ~40cm/15,75" "Cold Ellipsoididal Reflector"?
Gladly a source in Germany.

With this reflector and the 1mm-groove-pitch-Fresnel (August > 3DLens) I can build a high-quality-beamer.

Which big objective where ideal for this beamer?

Tobias Claren
Re: bad news

Guy Grotke said:
>Where can I find a ~40cm/15,75" "Cold Ellipsoididal Reflector"?

You would have to have that custom made and then coated. It would cost more than your house!

Sometimes the art of design is to find a way to re-use inexpensive mass-produced items.

Why? If there is that small, why not more largely? Therefore I look for a source.
slize said:
here is a link where you can find ellipsoidal reflectors the size you are looking for:

for an objective i would say leitz wetzlar 400mm FL with 13,5mm DIA


Average Life 1000h

Color Temperature 5500±500K
Has it only a reflection in this range?
The lamp I use, has a specific Color temperature.....
OK, this lamp-color-temerature is in this range, but why a range with the reflector?

There is no "D2"? I need inside approx. 40cm.
There are no prices?

Are there other reflectors? Gladly like Edmunds in Germany.
Re: lamp & reflector

Guy Grotke said:

I tried this drawing exercise for both the Edmund's elliptical reflectors, and it looked like they were not very good matches to available fresnels for a 15" LCD.

How about use an aspherical condensor lens right at or before the f2? It would enlarge the light cone after the f2, right? Since you have the ray trace software, could you try some condensors from this company:
the openning of the 97mm reflector is 89mm, the f2 is 96mm from the opening plane.
reflector & aspherical lens

Sorry, I don't know how to model an aspherical lens in the free downloadable version of OSLO that I have. But when I said "drawing exercise", I meant drawing with a pencil on paper.

I made a two dimensional full-scale drawing of the reflector, condensor fresnel, and LCD, just to see what focal length fresnel I would need. I projected rays from the edges of the reflector through F2, and then out to the point they were 15" apart. That is where they should intersect the condensor fresnel. Then I measured the distance from the center of the condensor fresnel to F2. Anybody can do this!
without a condensor lens, the light cone covers about 7.8" area at 220mm from F2. This is perfect to screens that are 7" and under. In order to cover whold 15.4" LCD I am going to use, a condensor lens before F2 is needed. The condensor lens I modeled in the picture is :

Code No.``E.F.L. Diameter ø ` C.T ` E.T Aspheric R2 Material Remark
HL-AS-008 33mm 52 mm `` 32.56 ` 2.5 `` AS `` 0 ` B270

of course it is a very thick lens (32.56mm at the center), in real life its behavior wont be exactly as shown in the picture, but you get the idea.


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another option

18wheeler: Another option would be to use a weak negative lens after F2 to spread the diverging cone of light to match your condensor fresnel.

jaws2421: Neither of those will work. The latter is a flat mirror cut in the shape of an elipse. The former is a parabola, which does not work well in this tyoe of design. (The direct light from the lamp has different direction than the reflected light.)

Look at Edmonds to see some pictures (and prices) of cold elliptical reflectors. They also sell some spherical reflectors, but those are easier to find or make.


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