I plan on using my projector in varying locations, and have an idea about a lens solution for focus, but how would the picture look/ be corrected if the placment of the projector was to the right of the screen as shown below. would the picture look right? I know it is a silly question.



________

screen^


|couch|
----------------- X <- projector

Actually it would be very keystoned. Some keystone can be corrected by using a fresnel in front of the LCD panel. I believe the maximum amount of keystone correction from this method is about 20º.

When fixing the keystone do you actually tilt the fresnel, in front of the LCD, until the screen appears correct? I'm thinking of mounting mine (if it gets built) on the ceiling and would have a similar problem.

Mike, yep that's exactly how you do it. Some builders even have their collector fresnel mounted to a knob that they can turn from the outside of the box. I will be implementing this design in my next projector, the 7".

It is important to note that care should be taken to keep the fresnels perfectly flat and rigid. If you are going to make a movable fresnel for keystone you must devise a way (frame) to keep it rigid. Any warpage will distort the picture. Also of note especially when using a fresnel in front of the object (lcd panel) is the necessity to keep the lens scrupulously clean. Wear disposable rubber gloves when handling these optics, cutting them etc. Cleaning these lenses is NOT easy. Dust can be cleaned away with a new paintbrush. Finger oils etc are much more challenging (grooves) and if you try to clean it with solvent (alcohol) you may find that the lens never performs satisfactorily again.

Also: Mike if you're planning on permanently installing your projector, you can simply ascertain the keystone correction you need and mount you collector fresnel to a piece of thin (.125) glass at the proper angle. The glass holds the fresnel flat. Try to use the thinnest glass you can (not tempered) as this will cut down on refraction and transmission losses.

so we are talking the double fresnel before the lcd, the lcd then a single or double after the lcd? also how far would the placement be, i assume with focal lengths accounted for this will increase the size of the box itself. basically a 26" box is too big for my available space, so if i could shave 10" off it would be ideal.

Nope, in this case the double fresnel is split, and the second is placed after the LCD, at an angle to correct the keystoning.. DIYLabs sells pre-split double fresnel's though apparently it's not too difficult to do it yourself.

If I understand this right, the front fresnel lens needs to tilt up and down and side to side? I understand that if the projector is above or below the screen then the front lens needs to be tilted to fix the keystoning. Do you have to do the same thing in the horizontal plane? I'm not trying to make this harder than it has to be, I'm just a little confused!
Thanks for any help.

You can do it horizontally if you need to.