Lens Help

[Gonthorn]

Hi all

I have a big problem, that is I can't find the proper projection lens for my projector.

Here are my specs:

17inch lcd monitor
15 by 15 inch fresnel lenses (focal lenght of 9 inches)
500 watt light source

Now my problem:

I want a lens (or want to design a lens like make my own doublet / triplet that will work) for this area:

10 foot throw distance, 5.2 or so times magnification ( want to make the 17 inch screen be around 90 ish inches). But I can't figure it out. There has to be some equations out there that can tell me the FL to use / diameter and all that.

So If anyone can help me out that would be great. Im looking for numbers here, or at least an equation that will get me numbers. I don't want to aimlessly buy the wrong triplet not even knowing if it will work before hand.

Thanks for any input

 

[mparker]

check out the lens theroy section of alans site, there are some equations at the bottom of the page
hopefully this will help you out

http://diyprojectorcompany.com/theory/lenses.htm

 

[Gonthorn]

I still can't find what I need 🙁 I'm looking for a lens (triplet) that will focus a 17 inch diagonal image completely at a distance of 10 ish inches ( my fresnel focal lenghts are both 9 inches so thats where the light is getting focused).


I cant seem to find a formula to make this work PLEASE HELP.

Ill grind my own lenses if only I could figure out what 3 lenses need to be put in this triplet.

Thanks for any help