Hello. I cant find a thread to help me choose whether I should do a split or unsplit fresnel configuration.

I'm basically confused about what each set up is. Does unsplit just mean 1 fresnel in between the bulb and lcd? and split means one on either side of lcd?

does each set up change what FL fresnel you would want to use?


heres my proposed set up:

Syncmaster 730b 17" LCD
LL Standard triplet
400w metal halide with Eballast from hidhut

220mm fresnel (behind lcd?)
330mm fresnel (between lcd and triplet?)

both lenses from 3dlens and 395mmx395mm.

If i were to do unsplit, should I change from a 220 mm fresnel? I am confused.
thanks for any help!

if theres any thread that would help me with this please point me there

There is some mild debate regarding ALL the benefits and downsides of split versus unsplit but the short answer is if you need to keystone split; otherwise go unsplit.

split --> reflector / lamp / rear fresnel (220) / LCD / front fresnel / triplet

unsplit --> reflector / lamp / rear fresnel (220) / front fresnel / LCD / triplet

So, you've got the idea.

The front fresnel focal length must be "matched" to the intended triplet.

The rear fresnel focal length determines how far away the lamp must be placed from it.

Due to light losses over distance and all other things being equal the shorter the rear fresnel focal length the more light you can gather to ultimately project through your triplet.

The wiki should help and some pinned topics will also enlighten you a bit.

doesnt the unsplit setup cause there to be more light in the middle of the image and less near the corners?

is there something preventing that from happening?

I have a commercial projector, Ask 970 impression projector, and it uses an unsplit configuration. Edge to edge are sharp and evenly lit. If I was considering an unsplit setup, I'd shoot for this configuration.







Victor

Totally homogenous illumination over 100% of the projected image is pretty much an unreachable goal. Your eyes will tolerate a fair amount of drop-off in light intensity at the edges/corners.

The forums cover some methods to assist in getting more even illumination.