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DIY Projector Theory

Projector A

Figure 1 The components

The diagram above represents the side cross section of a typical projector that employs a 'Split Fresnel' setup.

  1. 80mm fan (12V or 240V its up to you)
  2. PJ-PCON 90mm Pre-condenser Lens (helps scavenge stray light rays)
  3. PJ-150M 150W Metal Halide Lamp
  4. PJ-G12B G12 Ceramic Base
  5. PJ-RF74 Pro Reflector. Dichroic IR Pass. Theoretically doubles light output. 44mm from the centre of the lamp envelope.
  6. PJ-UVS1 UV Resistant Lexan panel. Our lamps are UV cut, however this also helps with heat isolation.
  7. A removable panel with air conditioning foam filter sponge.
  8. Air flow compartment - usually integrated into the enclosure itself
  9. PJ-1003 Pro Condenser Fresnel Lens (Trim to suit your application)
  10. The LCD Panel
  11. PJ-1002 Pro Field Fresnel Lens (Trim to suit your application)
  12. PJ-2500 Pro 100mm Diameter Triplet Lens mounted on a slide to allow focussing.
Projector B

Figure 2A The light path for this 'Split Fresnel' setup
Projector B2

Figure 2B The light path for this 'Un-split Fresnel' setup

Let us compare 'split' vs 'unsplit' Fresnel lenses setup:

LCD is placed BETWEEN the Condenser and Field Fresnel Lenses ('Split Fresnel' setup):

  • Best uniformity in light distribution over LCD panel
  • Fresnel lenses only need to be slightly larger than the LCD panel
  • Contrast can be affected
  • Slightly longer focal distance to triplet

LCD is placed AFTER the Condenser and Field Fresnel Lenses ('Un-split Fresnel' setup):
  • Excellent contrast
  • Slightly shorter focal distance to triplet
  • Simpler to build, as the Fresnels can be sandwiched together.
  • Easier to align the grooves of the Fresnels
  • Unless enough Fresnel area is overhanging the LCD panel, dark edges can be noticed.

Projector C

Figure 3 Air flow paths within the projector

Keeping with the flow of cold and hot air, the projector's airflow system usually entails cold air entering from the bottom, and cooling the front side of the Condenser Fresnel and the back side of the LCD panel then flowing past the lamp and switch gear and out the back of the projector.

If you want more detailed information you will have to enter the PJOZ Online Learning Centre which in available in our Courses category. We charge a modest fee to access our information as our authors are retired teachers and need to make a living from their life-work.

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