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Old December 27th, 2004, 12:08 PM   #76
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I am "digging" into this matter. I will let you know if I find out anything of interest.
Did you check the tech info from beattie?
How they make the difuser and the Fresnel?
Just in case you missed it, it's here:
http://www.intenscreen.com/pdf/focusing_screens.PDF

I am no biased in any way and ready anytime to switch for
better (providing it can be demonstrated to be better for the purpose!!)
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Old December 27th, 2004, 12:50 PM   #77
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Very interesting Dan. I can't tell precisely how or what the screen is made of from that PDF. It seems to be a fresnel made with holographic processes? Interesting...

Anyway, I'm going to be getting a holographic diffuser to play around with so I'll post when I have some results.
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Old December 27th, 2004, 03:46 PM   #78
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yes, let us see some pics.
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Old December 29th, 2004, 02:38 PM   #79
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Okay guys heres the low down on all of these diffusers your mentioning. Sadly I've been posting on this project since the very begining so I've heard all of these diffusers being tested for this purpose. (According to what was posted):

Holographic Diffusers are simply diffusers that have highly diffused characteristics. By doing so they create a image that is unlikely to create a hotspot because light is diffused at a much wider and even angle than traditional ground glass. This is good when it comes to getting rid of the hot spot BUT this also creates a problem. Since the light is going in all directions only a small portion of it is actually directed towards the CCDs. This means the image is much darker than traditional GG. Not good. Now they come in different versions with some less diffused than others but it was determined even the brightest wasnt nearly as bright as GG.

Beattie screens are regarded by most photographers as the brightest screens. I've tested them and they are indeed bright but there is another much smaller company out there that makes screens that people swear by. The company is called Maxwell Precision Optics. Thoughs that have owned both Maxwell and the Beattie insist that the Maxwell screens are even brighter. I've tried them both out but never side by side. I own a Maxwell and I'm happy with it. The reason the Maxwell may perform better is the fact that the fresnel lens is both finer and can be ordered to match a given focal length. In other words you can get one that can be perfectly calibrated to your system. No hot spot, bright and fine fresnel lens. However the company is so small they dont even have a website. I did a search for it to find the address and phone number. The owner is a Bill Maxwell and a incredibly knowledgeable guy when it comes to optics. Thoughs thinking about using it for a static adapter might want to keep looking though because while the grain is small isnt not too small that you cant see it. And if you are making it oscillate it better be a very very small movement because you have to remember once you make the PCX lens (fresnel) and the GG one they are forced to move together thus their focal point moves as well. If it moves too far off center of the CCD you'll get a hot spot again.

If you are looking for a focusing screen that is as grainless as they get look at the laser etch screens in the new pro model Canon EOS bodies. They are incredible BUT (dont you hate that?) they dont make them without markings. Find a way to get it without markings and I'd think you'd be in business.

Brett Erskine
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Old December 29th, 2004, 03:31 PM   #80
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Brett,

Thanks for passing this one by.

I did not know of Maxwell (I knew there were others) but did
not bother to look them all up front. One of the best is good enough for a "proof of concept".

(from what I know, Beattie also can do custom focal lenght on the Fresnel, but that is a lot of money)

About contrast.
When I first ordered from them, I specifically requested a bright but low contrast screen (or if they can make one) Tough luck.
Reason: a lower contrast would act as a better "translator" between real life contrast ratio (sometimes as high as 14 stops) and the CCD's limited range. (less than film anyway) I hope this helps.
That awfull hi-contrast (aside from huge DOF) makes video look as it does.

Just a thought for the non moving concept. If the image form
the grainless GG is good enough on a 50" plasma (and it doesn't show any patern) than that might be the solution.
(although some might be tempted to print on film (for theatre) from HD )
Well.....looks like we can't have it all.
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Old December 29th, 2004, 04:09 PM   #81
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Brett,

How sure are you about the holographic diffusers? I see no reason that they should exhibit the characteristics you have given them.

You can define how spread out the light becomes from several degrees into much larger numbers. These are used in TVs and monitors all the time precisely for their ability to show a great image. Who tested the holographic diffuser in the past?
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Old December 29th, 2004, 04:44 PM   #82
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somewhere in times past someone tested the holographic diffusers. I just can not find it
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Old December 29th, 2004, 04:52 PM   #83
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Neither can I. I know these things are used in projection displays as well so they _can_ work... somehow.

I suspect the person tested the material using a LSD that had a high angular divergence (60+ degrees).

Just a guess though. I may be entirely wrong!
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Old December 30th, 2004, 12:44 AM   #84
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Just sent off an email to POC detailing our specific needs and asking for guidance. I'll let you guys know if/when I hear back from them and whether they think their materials can be benefitial to us.
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Old December 30th, 2004, 01:40 PM   #85
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Once again I wasnt the one who tested the holographic diffusers so I cant tell you first hand. I only recal what others have said about them. I wish I could point you to all the post when it was a hot topic but I dont know where they are. You'll notice though that they didnt say it wouldnt work. In fact they did but it would be much too dark. I know it has a cool name ("holographic") but they arent doing anything magical. Just think about what light is doing when it hits a diffused surface and how much it would have to be diffused in order for it to appear equally bright from different angles. Very diffused. Its a physical impossibilty for a diffuser to be viewable from multiple angles AND be bright. This is why they are using less diffused GG and field lenses and/or fresnel lenses in cameras to focus the light where it needs to go.
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Old December 30th, 2004, 02:14 PM   #86
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>>>>>>Hi Dan,

Thank you for your interest in POC. Depending on your source divergence, it is possible that a diffuser will work without the Fresnel lens. If you have a large source divergence, you can laminate a POC diffuser to a Fresnel lens. The Fresnel lens reduces reflection and scattering losses.

Best regards and happy new year,
Jeff Laine
POC>>>>>>>>>>
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Old December 30th, 2004, 08:49 PM   #87
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Brett,

I see what you mean. However, how diffuse you get can be precisely specified in the manufacturing process. Anywhere from percents of a degree to full blown 180.

What effect this would have upon the ability to remove hotspots I don't know. In any case I think the real benefit that these *may* provide is a very high transmission efficiency - especially with the ability to precisely control where that light is going (even if you end up with a hotspot).
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Old January 1st, 2005, 06:05 PM   #88
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Aaron-
You just answered your own question. The angle rating of the diffuser IS how you can tell how effective the diffuser will be at removing the hot spot.

As far as their transmission efficency I would recomend going by what others that have tested them for this project had to say. They said they were too dark.
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Old January 1st, 2005, 06:08 PM   #89
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Yeah I seem to be good at doing that sort of thing :D. Ah well...

I'm still going to find one to play around with though. Just in case I can get decent results. It's too bad that there have been negative comments about them. They could have been a very good solution!

On a side note: does anyone know where to find lenses large enough to work with MF? I'm having trouble finding this sort of thing for my project.

EDIT: Lenses as in condensers, cylindricals etc not actual MF lenses.
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Old January 1st, 2005, 06:20 PM   #90
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Edmunds Scientific, Surplus Shed or Anchor Optics. Google it for the web sites.
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