ok i have a 8.75" lcd and a 17" ohp frensel i was about to cut it to the exact size of the screen but i thought i should check if that is right.
I wanted to cut it down to 8.75" so it would slot into theframe of the lcd.
pic.....

Pretty sure you want your fresnels to be a bit larger than the LCD on all sides (1/4"-1/2").

well is it bad to have it how i want it?

Click to view attachment
the fluffy thing in the corner is the dog

just remembered that it will technicaly be 4mm bigger than the area of pixels
someone tell me if its ok

are you using a split setup or unsplit. for a split I think 4mm larger would be fine.

no the frensel is unsplit but i might split it when i cut it
does it make a difference if they are split or unsplit also if i do split them then can i put the second on right upto the lcd like the rear one?

you don't want the lenses directly against the LCD in any configuration. split vesus unsplit makes a difference in fresnel size. for a split setup, the fresnels can be close to the size of the LCD. I would recommend still slightly larger to help thwart off dark edges. for unsplit setup, they definitely need to be larger, but the size depends on the size of your LCD, triplet, and collector fressy FL. see pic below for explanation



in split setup, the light will be parallel between the fressys and the LCD should be completely covered by equal sized fresnels. in unsplit, the light will already be converging towards the lense when it hits the LCD. the fressys need to be larger than the size of the LCD so the light cone they project will be large enough by the time it hits the LCD for coverage

ok so I don't cut them down to the screen size.
the screen is 8.75" so would 9.5" be good for an unsplit setup?
What are the advantages of spit vs. unsplit?

anyhelp?

This is a big discussion topic me thinks. They're almost equal in image quality, but if you want to adjust keystoning, you have to spit.


Sorry about that, couldn't resist.

unsplit produces the best picture quality as there is nothing between the LCD and triplet... but depending on your PJ placement, you may need keystoning ability... in this case split is likely the only choice you'll have.

cheers,
gs


edit: thanks to Durachko keeping me honest I changed my original "unsplit" to "split"... which now appears in bold...

May be somewhat off-topic but may provide info to the primary poster if he does a vertical:


Unsplit configuration + vertical one mirror fold setup = what changes to the light path measurements if any?

in other more clear wording: What changes to the light path measurements are there, if any, for a vertical setup and using unsplit fresnels?


i'm thinking it wouldn't change much except the 40 mm or so between the fresnels and lcd

with an unsplit design the distance from the LCD to triplet would be the same as the distance from LCD to mirror + mirror to triplet. The fresnels don't really come into play too much with an unsplit design unless you are trying to maximize brightness or maximize "evenness".

gs