I need some help with where to place the condenser. Can someone using a similar setup post their fresnel - lens - lamp distances.

I have tried alot of stuff, I think I got a resonable setup (lens- lamp almost touching, lamp arc - fresnel about 220mm) ... but it doesnt make sence with respect to what I have read .. the arc needs to be closer to the fresnel, at around 170-190 ...

but that doesnt work ... I get a hot spot with very pale outer image .. (if I move the cond. lens towards the fresnel I get a brighter center about 1/8 of the screen and very very dull outer image) ... I only get good light disto if I move the lamp back and keep the cond. lens close to the lamp ..

so I need some guidance here ... thnx

setup:

22" triplet - 630 fresnel - 17" LCD - 220 fresnel - 6x9 precon - 150W Powerball - reflector

I wrote the above post in a haste hoping someone would answer before I quit ... I guess I need to give more info to explain what I am doing .. maybe someone might be able to help me understand whats going on

in dazzlas precon calculator:
Triplet
Diameter 110 mm
Thickness 140 mm
Center of Triplet to LCD 559 mm

LCD
Diag 431,8 mm
Distance to fresnel 20 mm

Fresnels
Gap between 40 mm
Collector FL 220 mm
Condenser FL 630 mm

Arc
Length 10 mm


Pre-condenser
fl= 228,6 mm
n= 1,474
Diameter(d)= 152,4 mm
Edge Thickness= 3 mm

Fresnel to Plano= 172,6093328 mm
Plano to Arc= 8,868383907 mm
Arc Collection Angle= 165,2400749 deg

I realize the calc is for unsplit setup but I thought it would still give a rough idea about the placements. since this is what I did for my old precon - which broke due to heat - and got pretty good results.

When I setup the pj using the distances close to the values above I get a horrible light spread. If I use the exact values I get a bright spot in the middle and rings of light around it fading away towards the edges.

If I only move the precon away from the lamp than the light starts forming a nice tight circle but much smaller than the LCD. so I get a big bright circle in the middle and the rest dark and dull ...

also when I start moving the precon away from the lamp the tight light circle immediately starts turning yellow, the smaller the circle the yellower it gets ... I never got this with the old precon which was plain glass ...


to get the well defined circle of light cover the lcd I need to move the lamp way back to 220 - 230mm from the fresnel. which is where the lamp was (even closer) with out the precon. when I place the precon in place I get a brighter image but the light disto is still not very well spread ... I get hot spotting in the middle and can see the edge of the precon in the corners - again with the light turning stilghtly yellow ....

I couldnt go back any further since I need to change the position of the balast and the wiring .. so I might just move everything closer the triplet .. it was too late and I was too tired (and pissed out of my brain) to continue fiddling around ...

any thoughts ?

I don’t think the 6*9 PCX lens is workable with a 17” LCD and 220mmFL fresnel, in fact a 15” would be pushing it. A 220mmFL fresnel is not a real good size to use in a pre-con set up unless the LCD is small. I don’t think there would be any meaningful gain in vignetting and may be worse than with out a pre-con.

A couple of problems.
The pre-con calculator isn’t set up for split optics but it can be fudged to get a rough guide.
If you look at the Plano to arc distance it’s only 8.8mm, the outer glass envelope of the powerball is 25mm which means the arc can’t get close enough to the pre-con.
The yellowing is chromatic aberration introduced by the fresnels. The reason you can see it is that the arc image at the triplet is focusing too short. This isn’t directly related to the pre-con glass type.

Just as a test remove the pre-con and the reflector. Move the lamp forward until you see the screen corners turn a blue. Mark this position and then move the lamp backwards until you see the screen image corners start to turn yellow. Half way between these two positions is the ideal placement for the arc. Now some questions:
Arc to rear fresnel distance?
Rear fresnel to front fresnel distance?
LCD to front fresnel distance?
LCD to triplet center distance?
Triplet center to screen distance?
Screen diagonal?
And I presume you are using the LL fresnels, 220mmFL and 650mm?

DJ

hmmmm ... I thought 6x9 was a good lens to be used with 220 fres. well thats what I read through out the forum at least...

that arc to plano (8mm) is bugging me, because before I ordered the lens I used your calc to find the best lamp by comparing plano to arc and collection angle ... for 6x9 I have 14.77 plano to arc, and coll angle 158. now I cant repeat the values in the calc .. I think I might have messed up once again ...

I had the lamp positioned exactly where you described .. blue/yellow mid point ... I dont know the distance by heart, I have it marked on the pj .. I'll post the measurements you asked for tonight ...

btw I also have 330 fres. that I just replaced with the 220 .. I'm going to try that out too with the 6x9 ...

Maybe this will help, this was a drawing done in one of the pre condensor threads.

There’s been a lot of talk about using them but I don’t think I’ve seen one used successfully. Elken has used one but he predominantly uses wide screen, corners weren't an issue. AV has tested it but I don’ believe that the fresnels were used at their designed specifications so light loss will start to creep in from the corners, aka hotspot.


Using your numbers I might be able to give you some meaningful distances.

DJ

dazzzla,

thats what I ended up with last night. I did alot of trial and error to get a decent spread. the best light disto I got was with the lamp at around 240mm from the 220 fesnel with the precon almost touching the lamp ... which really doesn't make sense to me ...


the image had noticeable hot spot (on white image - not so in movies), cut corners (acceptable for now) and slightly washed out blacks ...

I was too anxious to get it to work, so I didn't take all the measurements you asked for ... hopefully I'll keep my cool tonight and take measurements before I fiddle around with it again ...