So many builders had made a wrong choice when buying projection lens. So here is the guide ,

Important factors to consider when buying projection lens in this site. This is also the initial step before starting the project. After you decided what projection lens to buy, the rest will come easy.

1. Projection lens (also lcd size) dictates the throw distance and image size

2. Cost factor

To compute for the focal length of PJL ( projection lens) that you need, you have to decide for yourself your target image size,throw distance and lcd size

Use this basic formula

PJL focal length= (throw distance x LCD size)/image size

So look at the set-up in your home and determine the

1. Image diagonal size in inches that you want

2. Decide on the LCD size in inches

3. Determine the throw distance- determine how far from the screen/wall you want to place your projector. In my own experiences, back of the room placement is best for diy projector. This eliminates keystone problem, wont block your views at your sitting position, easy maintenance,cabling and has higher WAF ( wife acceptance factor)

Note: convert the unit in mm after you compute for PJL focal length. (1 inch=25.4mm)

For example:

LCD size: 7 inches

Throw distance: 12ft or 144 inches

Image size: 120 inches diagonal

PJL focal length= (throw distance x LCD size)/image size

PJL focal length= 144 x 7 /120

= 8.4 inches

= 8.4 x25.4

= 213mm

The nearest available focal length for using 7inch lcd is F-210. So buy the F-210. Check the recommeded PJL <B> with F-210

Note: keep in mind that whatever focal length you choose, you can still change image size by

moving the projector away or closer to the screen.

Now if you already know the focal length of PJL and the size of LCD, you can now select the projections lens that is available on this site.

A>For 10.1 inch lcd

1. F-240 OHP lens- 2000 pesos

2. F-345 OHP lens- 1500 pesos

3. F-315 w focus ring- 3000-best for 10.1 inch.

B>For 7 inch lcd

1. F-210 Prime lens- 4000 pesos-The best projection lens here. Cost more but may help you decide to lower the led wattage because this lens produces the brightest image among the lens that is sold here.

2. F-220 triplet w/ focusing ring- 3000 pesos- Cheaper than prime lens, but a little lower brightness. But produces perfect focus on all corners easily.

3. F-240 OHP lens- no focusing ring.- 2000 pesos

4. F-345 OHP lens- no focusing ring.- 1500 pesos

C>For 5.6 inch LCD only

1. F-210 Prime lens- 4000 pesos.

2. F-210 w/ focusing ring- 3000 pesos- Near performance of prime lens

3. F-220 w/focusing ring-3000 pesos. Focus at sides and corners is better than prime lens and F-210.. resolution is better . A little lower brighness than (2) F-210 and prime lens

2. F-240 w/ focusing ring- 3000-pesos-As good as F-210

3. F-240 OHP lens-2000 pesos

4. F-345 OHP lens-1500 pesos

So when you have 10.1 inch lcd, check all the lens at A

For 7 inch lcd, check all the lens at B

For 5.6 inch lcd, check all the lens in B and C

I hope this minimizes confusion especially for newbies.

Another tip For those in a budget. its better to buy a Prime lens than buying a higher wattage led.

Low wattage led is

1. Cheaper

2. Cheaper heatsink, less heat

3. Low power consumption

4. Smaller box

5. box is cooler

6. LCD is cooler,longer life

7. Can use smaller fan, lesser cost, lesser noise and less power usage.

8. led is cooler, longer life.

Dear Hertz,

Thanks for such a nice guidance. There are some calc from lumenlab available for calculation the Triplet lens focal length,t LCD size & Projection distance.

The main issue is no where there is any formula to calculate the FL of Fresnel lens.

What I request you is please write something more to make us understand the relation of Focal length of Fresnel lens with Triplet lens.

What FL of Fresnel lens to choose in case of different different Triplet lens.

What difference it makes for same Fresnel with various Triplet.

Thanks in advance.