Ok here is a photo, this is the result of all my research so far in the chase for perfection,, however every time we advance, weakness's show up else where.

I will cover this more fully soon,, but needless to say not all fressies are equal, and this applies to all brands, this has been brought into full view since playing with higher contrasts, and brighter images, and goes a long way to explain some of the very varied problems that we have all experienced, and had no real defined answer for. but there are also many other things that can confuse this whole issue too, so its very easy to jump to a wrong conclusion..

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these are actual flaws in the fressie, this is a pic of a 650mm one.

method projector LCD turned off so just white light is being projected, the fressie has grooved side facing triplet, and fressie is about 18" from screen..

you can see the banding effect, this shows that the density/thickness of acrylic varies, causing the banding, now this also plays havoc with glowies too,, and lamp optical axis misalignments augment the errors even further,,,, heheheh smoke and mirrors effect

to me this is almost the final link in the very long chain of events from last september05 when the whole saga really began with SIM's all very famous,,, ( hey guys I have a scratch on my panel, what do I do to fix it)... twas a bit like apollo 13,, ( hey Housten we have a problem) hehehehhehe

but yes,,, I feel as tho,, this seals it all to actually have a touchdown, and build my final version PJ,,, Yeaaaa

ummm till I do sumfin different again, at least

So by these examples would you say that the banding in the fresnels thickness and mis alignment cause adverse polarizer effects that lead to glowies? Those thick-thin bans would also bend the light off it's intended path too, ya think?

I ordered a 575mm fresnel from Edmund Optical ($85 ) and was surprised at the extra thickness of it, I haven't measure it but its much thicker that LL, 3dlens or DIPCs fresnels. It's still acrylic, just thicker, it does have a strange ghostly stretch like defect in the middle but it doesn't effect the projected image. This defect hasn't deformed the rings so I kept lens and I'm happy with it's performance. Not the price though.

Here's a summary clip from my "glowies" thread:

So here's my list of "glowie/backlight bleed" improvements:

1) Tape edge of panel glass with light-blocking tape without covering visible edge pixels. (I used electrical tape).
2) Paint all mounting frames, especially frames around panel edge flat back. Paint any other colored surfaces flat black.
3) Be certain your lamp arch is positioned at your rear fresnels focal point (creates even, parralell fresnel transmission) and all optics are in the best alignment possible.
4) Fix light leaks while maintaining sufficient air flow.
5) Vary your fresnel spacing.
6) Rotate polarizer - if replaced.

My experience shows these steps will benefit a split or unsplit setup. I now believe any combination of these issues will make your "glowies" unacceptable. I hope my obsessive behavior will save other glowie club members some time and frustration.

at the moment in a partial rebuild,, using the new ""holy grail""

Ok

Here is the fresnel de_mystified,,, and an explanation for the many varied effects/problems/glowies/unevenlight/hotspotting/darkzones/ etc etc etc etc.

and why everyone has at times been chasing impossible cures for wrong reasons etc.......................

the setup first

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a cute shot,,, the circle of light effect
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ok first we have the 650mm fressie
first pic is outside focus

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second is inside focus

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nor for the 3dlens 220mm

first outside focus

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second is inside focus

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the 3dlens 330mm

first outside focus

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second inside focus

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this is the DIYPJ 330mm,,

now despite its famous as per DAZZLER old avatar,, the starburst one,,

it has a very clean image,, no real defects as per say

first outside focus

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inside focus,, the "starburst"

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here are some oldies,, but sort of goodies

the LL std 15" 330mm

outside focus

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inside focus

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now the best is strangely enough the very original rounded corner std 15" fressie,, it is the brightest of lot
and thicker too..

220mm

outside focus

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inside focus

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so,, if you stop and study these images,,, you should understand the why and whereforths, of all the results everyone has been getting..

in other words every fressie is very unique, and has its own signature of issues,,

I for one had very good results with the dual DIYPJ 330mm fressies,, now I know why

a while ago I was doing all sorts of image "anal" stuff,, but I had a persistant darkish top left corner, no matter what aligning i did with optics,,, it was always slightly egg shaped and always dropped off in top left corner,, if only I had of rotated 3dlens 330mm fressie,, it would have swapped to bottom left corner,, hehehehhe,,, live and learn

so a motto,, if you are chasing something you cant resolve, rotate your fressie and see if issue follows,,,

also bright centres,, well they are the nature of fressies,,,, look at pics,, they tell you why

and dull corners samo samo..

glowies,,, this is a six dimensional model,, I might try to simplify this another time,, but you need to understand how interactive all of this is, to begin with,,, and more importantly "why"

Thx for posting... very interesting

Nice to see the comparisions...makes you wonder what is the best fressie out there !

So far the OHP rounded has it ?!

not OHP;;; it was the original 15"std LL fresnel set, back in 2003

nice pictures ... interesting how much defect the lenses project

one other experiment that would be nice to do is the keystone capability of the fresnels. this is a problem I've been struggling for a while without any solution. I cant get proper focus what ever I do, what ever angle I set .. it is very frustrating...

So it would be nice to know upto what angle each brand/pitch fresnel will give acceptable results ... just an idea

Elken, you can also get a 3D projection of the defects, very similar to your waterfall graphs. Just angle the fresnel. You can even see the point of nothingness. Try it, you’ll be fascinated.

DJ

this a bump reminder, in connection with polarisers,, and effects etc...

Elken...now that you have several freznels, have you compared differences (preferably with ceramic-lamp) between the .2 & .5mm pitch's (and varied FL's) of those from 3dlens...as opposed LL's?
And would you still say that 220's are too-short for condensers, or only if pre-con's are used?

Yes eleking, if you could add some more fresnel info (fresnel pitch) to the pics it would help alot. Really interested in the pitch and egde thickness. Seems like it wouldn't be that defficult. Thank you for all your experiments.