Here is what i plan to use. I can vary these optics slightly but i need to know in which direction and how much. i will be using either a 8 inch or 7 inch lcd.

180mm fixed focus lens triplet
Dia76.4mm - Focus127.5mm condensor lens
Reflector Dia64mm - Focus16.3mm
Heat Filter IR 113x138x3mm:
FS Mirror 200x150x3mm:
fresnel 165mm x 105mm x 2mm - Focus 160mm

Suggestions?

How big (diameter) is that 180mm triplet and where did you find it?

not sure i have to ask. it is for ohp diy projector thought so im sure it will work with a small lcd. your not thinking of using for a 15 inch are you?

No. I was just curious. It's a pretty small FL for an OHP triplet and I wonder how narrow it is. If you can fit your LCD within it's FOV, that's great, but keep in mind you will have a fairly short throw.

ok. yes ive done the calculations and i get the right size image i want.

Can someone explain to me why exclusive online has this configuration setup with a 240fl condensor lens and 160mm back fresnel?

Reflector + 1mm to HQI + 23.85mm to condensor + 136.15mm to fresnel + 285 to 330mm to objective.

If the condenser is a 240mm FL then should this not match the back Fresnel FL?

For smaller panels and a smaller box then it is good to use a shorter FL rear Fresnel.

The real limit to how short the rear FL can be is the arc size at the triplet. This is determined by the front to back fl or ratio.

Arc image at triplet = arc size x front to back ratio

For a 20mm arc lamp and a 220mm/220mm Fresnel setup the arc will be about 20mm at the triplet.

For a 20mm arc and a 110mm rear Fresnel and a 220mm front fresnel, the arc image will be 40mm at the triplet. (Front to back fl = 2 to 1 the arc will be twice as large at the triplet.

It is best to work backwards from the triplet to find either the largest arc that will fit or the shortest rear fl that can be used.

You could call there triplet a 300mm x 50mm triplet so the largest arc image that will fit inside the triplet is 50mm. If we call the front FL 300mm and you have a 25mm arc lamp then the shortest fl the rear Fresnel/ condenser system can have is 150mm.

When you add a 240mm fl condenser lens to a 160mm rear Fresnel the total fl will become shorter to some thing like 110mm effective fl. At this point using a shorter fl condenser will not make any more LUX, all the light will just miss the triplet because of the arc image becoming too large.


A 220mm rear fresnel and a shorter fl condenser will give better vignetting but be only slightly brighter than the 160mm fresnel and the 240mm condenser.

You triplet should be from an opaque pj and should be about 4" in diameter so a vary short rear fl will work well and make a vary bright PJ.


I would try to get that 160mm rear fresnel if you want a small box.

Ok well i do want to use a 160mm back fresnel because i figured the fresnel would be 160mm from the arc which is much much brighter then the fresnel being at 220mm from arc. Now I do want to include a glass condenser lens here. So if i use a 240mm FL glass condenser placed at say 15mm from the arc does this change the FL placement of the rear fresnel? Another words does this mean the 160mm back fresnel is no longer placed at 160mm from the arc? Where does it go and how do i calculate this?

My calculations were that if i used a 160mm back fresnel compared to a 220 my light would jump 100% or double in intensity. Since I plan to use e double ended 150w hqi this is necessary.
Yes i do want a small box you are correct.

Now if I can get that back fresnel at 110mm from the arc that would be even better. what glass condenser do you recomend to make this happen or should i just exclude the glass condenser all together?

I believe my arc size is about 20mm so using 110 back fresnel and 200 top fresnel the arc size at triplet will be about 36mm. The clear diameter of my triplet i think is at least 50mm so i am fine correct?

Also please help me chose the right FL reflector.
I have a OHP reflector laying around then i experimented with my 150 hqi double ended bulb. I took the bulb and placed right up agaist the reflector as close as possible.
When measuring from the center deepest point of the OHP reflector to the center of the arc (as if disecting the arc length wise) I get 26mm. Is this what the FL of the reflector should be?

If I was to use a 16mm FL reflector would this compromise my light engine?
I should also mention that while I am splitting the fresnels to eliminate rings they will both be behind the lcd. So i guess this is called non split still since lcd is not in between the fresnels. Does this change the equations at all?