# Help with 10.4" lcd...what lens?

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#### jaws2421

I am very newbish when it comes to optics. I just had a question that im sure someone out there can assit me with. I am going to be using a 10.4" sharp lcd 1024x768 natvie (pulled from an ASK Impact WSX). I wanted to know what type of lens I would need If i wanted the lens to be roughly 7-8 feet away from the 60"x60" screen? I know there's some more math to determine a correct FL, but I just wanted a good starting point. Thanks

#### Rox

ok, lets do a fast calc;

60" x 60" (strange image rate yours )

well, lets say you need 60" wide and have 10.4" diagonal lcd (8.3" wide). Then your desired magnification is 60/8.3=7.2 roughly

the realtion on the trhow (7.5 foot averaged fron your 7-8 range)
and the lcd to lens distance is 7.2 because this is the magnification you desire.

your trhow is 228cm and this means; 228/7.2=31.6cm is lcd to lens distance.

finally to work out the focal lengh of projection lens so your desired trhow/image size would be the good ones you need this:

1/F=1/228 + 1/31.6

where you found F=27.7cm is your desired focal for the projection lens. Try to find the closest one. Good luck

#### Rox

well, the surphushed lens (24cm focal) will give you larger image than your desired (if you place the projector closer to the wall it be solved)

the lumenlab is longer, so the image will be smaller, you need to place the projector fatrher from the wall.

just play with the variables, you need to decide what is the best choice for you.

#### Me2!

Rox! I'm surprised u didnt mention this

the 240mm fl lens will not project the whole image. It will be dark in the corners.

#### Rox

why do you say this?

#### Me2!

The same issue you chased for a long time with the 130mm triplet will impact this lens at 240mm.

What angle do you need the lens to handle for 15.4 at 240mm range? I didnt work it out but im sure it is much more than 40-45 degrees that a typical triplet can handle.

#### Me2!

Looks like about 78 degrees! No way it will work.

#### Rox

he needs like 50degrees full angle field angle on this lens from surphushed.

we don´t know if this lens specs will get to 50 degrees.

where did you get 78 from?

#### Me2!

390mm diagonal at 240mm range.

#### Rox

Me2! said:
390mm diagonal at 240mm range.

the two things are wrong

1)his lcd is 10.4" diagonal, 26.4cm

2)24cm focal lenght at 24cm from the lcd, is a wrong setup.

he needs to lace it at 27.3cm from the lcd to project his desired size image.

this gives us near 50 degrees field angle needed on the projection lens. I think this time, the lens fov should be good enough for him. (but the field angle should be checked, for ensuring)

#### Me2!

10.4"

I had 15.4" on the brain. Probably because ive been looking at the 15.4" lcds. My mistake.

Where did you get a 10.4" XGA??? I would like one!

#### jaws2421

I got it from an ASK Impact WSX, nice little screen. The model of the screen is a sharp LQ10PX01. Right now I have an apollo horizon II OHP, but i want something a bit compact that isn't right in my way when trying to watch something. Im most likely gonna mount the project on the roof when im done.

#### jaws2421

Thanks for your inputs guys, i think i may give the lumenlab's lens kit a shot. Hopefully it'll be far enough away from the screen.

#### jaws2421

yep, good ole ebay

#### jaws2421

Hey guys, if you're still reading this, would you think that the varifocal lens kit is good from DIYProjectorCompany.com ? Or should I just use the long throw or standard triplet. Right now im just considering the standard triplet, but in a week or so I could get any.

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