Hi Guys,

These are the lenses available to me. Can u please help me chose the right one?
DETAILS FOR OHP COMPONENTS

I) FRESNEL CONDENSER LENS – A4 SIZE

* SIZE : 310mm X 310mm
* FOCAL LENGTH : f = 216mm/343mm
* THICKNESS : t = 4.0mm
* PITCH : p=0.5mm
* PR : Deluxe quality – Rs 800/-

II) SINGLE FRESNSEL LENSES – A4 SIZE

* SIZE : 310mm X 310mm
* FOCAL LENGTH : f = 216mm OR 343mm
* THICKNESS : t = 2.0mm
* PITCH : p = 0.5mm
* PR : Rs 400/-

III) MENISCUS LENS :

* SIZE : 89mm
* FOCAL LENGTH : 11 inch
* CENTER THICKNESS : 10.20 mm

IV) TRIPLET LENS- THREE ELEMENT PROJECTION LENS

* BARREL DIA : 74mm
* F # : 5.2
* EFL : 315 mm

V) GLASS CONDENSER LENS

* SIZE : 60mm dia (39mm rad.. 40mm width)
* FOCAL LENGTH : 75mm
* CENTER THICKNESS : 15 mm


I am planning to make a 15" PJ.

1. * Out of the above (I) and (II) which one should i go for. and which focal length will be fine?
2. * What is a Meniscus Lense? Should i use it(how and where to use it)
3. * Should i use a condenser lens. I will be using a 400w philips matal halide lamp.will the condenser lens not heat up and crack?
4. * Where can i get a First Surface mirror in India?
5. * What is teh "F#" in the triplet?

I am sorry to bother u all with so many questions. But believe me i have written to many, but no one have reverted back.

Thanks and Regards

G V
Bangalore, India
9886717411

Note that the 310mm length restricts you to a 15" 4:3 monitor. It cannot be used for a 15.4" widescreen monitor.

The first fresnel (216mm/343mm) is an appropriate fresnel. This can be split into the two component lenses if need be, or will be fine as a single unit, so long as you keep them correctly oriented.

The meniscus lens is optional.

The triplet will be fine as is. The LL triplet is a bit longer in EFL, but not much.

I would also suggest that you get a good reflector. The LL reflector is excellent, but a good stainless steel reflector will certainly help.

Your questions:

1. I. You need both a collimator and a collector lens, this provides both functions.
2. Sometimes called a precondenser. It's value is fairly low in a 15" build with this FL fresnel, it's generally used to collect more light before it hits the fresnel lens.
3. See above.
4. A glass shop? Also, regular mirrors can often be used as first surface mirrors. The backing is usually just painted over the silvering, so if you strip the paint off, you have a first surface mirror.
5. The F# is a ratio of the diameter (aperature) of the lens. It's needed in photography, but not so much for projectors.

Thanks a lot SupraGuy for ur reply.



I am still not clear with one thing.which Fresnel lens should i order.? For my 15" LCD

Choices are

1) FOCAL LENGTH : f = 216mm, THICKNESS : t = 4.0mm, Cost: Rupees 800/-
2) FOCAL LENGTH : f = 343mm, THICKNESS : t = 4.0mm, Cost: Rupees 800/-
3) FOCAL LENGTH : f = 216mm, THICKNESS : t = 2.0mm, Cost: Rupees 400/-
4) FOCAL LENGTH : f = 343mm, THICKNESS : t = 2.0mm, Cost: Rupees 400/-


Question: which two should i choose.?? I will keep the LCD in between the two.

And ya. One good News. I got a LCD today from a second hand comp-goods shop.
It was only the panel and no cabinet.And to my surprise it also has a touch screen, but the cable for the touch screen's power supply is broken.so will have to work on it.

posting photos in my PLOG