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Old January 24th, 2006, 04:54 PM   #76
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Amazing. Truly outstanding.

I think I will upgrade my Letus ... with a pharmaceutical bag ;-)

I'm very happy about this possibility.
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Old January 24th, 2006, 06:55 PM   #77
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The POC solution is more like 4 F/stops! That's why it's not being used. Any chance of a few seconds of uncompressed DV on this? The stills look great!
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Old January 24th, 2006, 07:16 PM   #78
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Here is the spinning CD homedepot bag- night time, house across the street lit up with a porch light only. Compared to other things I have used in the past - this is gold - in the past, I wouldn't even be able to see it with mylar, wax paper etc.

http://dvstuff.250free.com/bag.htm

I also shot a small image with a light pointed away and behind a bookcase and it came out spectacular as well. Day shots in the next few days to compare.
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Old January 24th, 2006, 08:19 PM   #79
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Dan Diaconu did a Beattie/POC comparison, but it looks like he used a POC screen with an angle of diffusion of 50%. As Krishna says, there must be a compromise between diffusion/light loss somewhere with this material.
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Old January 24th, 2006, 08:45 PM   #80
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Quote:
Originally Posted by Francois Poitras
Dan Diaconu did a Beattie/POC comparison, but it looks like he used a POC screen with an angle of diffusion of 50%. As Krishna says, there must be a compromise between diffusion/light loss somewhere with this material.
Well, there is some wrong information somewhere. What is a POC 50%?

The POC screens come in different forms (sheets, films, etc) and in different materials (polycarbonate, polyester, acrylic, etc). So knowing the thickness and the type of plastic is very important. Then, the diffusion angles they offer are 0.5, 1, 5, 10, 15, 20, 25, 40, 60, 80 degrees for the circluar diffusion ones (rotationally invariant).

So I don't know what POC screen Dan was using for those tests.

I suspect that the best POC materials should be at least as good as the thin-films I am testing, which does not appear to be the case in those images.
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Old January 24th, 2006, 08:55 PM   #81
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Yes, we know at least the diffusion angle Dan used for his test. He said it was 50 degrees. I guess that is what he meant by 50%.

http://www.dvinfo.net/conf/showthrea...poc#post306340

It is quite possible POC offered this angle at that time.
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Old January 24th, 2006, 09:45 PM   #82
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Could be 50°, but we are still in the dark with respect to material and thickness, which seem to me very important. I am thinking that the screen Dan tested was not thin-film and possibly the angle is not optimal.

I just think that if I am getting much better light results from the materials I am testing, the POC guys must certainly have even better stuff. They show a graph where light transmission for a regular diffuser and a ground glass diffuser is at around 60%, and their materials are at 90% transmission. So it must be good.

Here is a DV AVI with two short segments:

http://www.filefactory.com/get/f.php...01e6c226bc1bbe

and a larger version:

http://www.filefactory.com/get/f.php...9476e79626f645

File was rotated 180 deg and recompressed as DV.

Last edited by Alain Bellon; January 25th, 2006 at 12:45 AM.
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Old January 25th, 2006, 06:36 AM   #83
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Quote:
Originally Posted by Rene Hinojosa
This is probably the device he's refering to: A Halina Viewer

http://www.danbbs.dk/~mikael/search/halina.htm

I don't know what gg he is using.
I got one of those secondhand for $5 or $15.
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Old January 25th, 2006, 10:30 AM   #84
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Perfect diffusion and perfect light transmissivity are mutually exclusive concepts. You can't have both. After reading a lot here, and doing a lot of experimenting, I'm pretty convinced there's no free lunch to be had in this department. From looking at intenscreen's tech docs, it would appear that intensescreen does a good job of diffusion, then immediatly redirects light back to the viewer using a fresnel...either as a condenser or a magnifier. I'm thinking that a fresnel mounted very close (like .1mm or so) to a spinning GG would offer similar? performance (about 1/2 to 1 stop gain)

Logically, to provide enough diffusion you need to scatter light to form an image. To much scattering = f/stop losses. Too little and you get my pro-mist low diffusion GG look. The only way IMO to get that stop of light loss back is to eliminate the GG altogether...but this would take a much larger CCD to duplicate the DOF properties of 35mm.
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Old January 25th, 2006, 11:03 AM   #85
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I think a fresnel lens will loose you res, and there is the possability of the camcorder pcking up the fresnel's 'rings'. The be honest, the frensel lens is doing the same job as a PCX lens, only slightly differently. But give it a go and see what you get.
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Old January 25th, 2006, 11:33 AM   #86
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Wayne, I think the advantage in integrated diffusion/fresnel solutions is that the fresnel is in direct contact with the GG surface, therefore max light redirection. I guess the question is, could you get a DCX that close without distortion?
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Old January 25th, 2006, 11:35 AM   #87
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Dennis, you are right. There is always a tradeoff. But I have found in my testing with these film materials, that I can get the same light transmission for different diffusion levels. So they may not be as mutually exclusive as we think. Of course you cannot have all light transmitted (not even a lens can do that), but we can try to get the best possible scenario. The advantage of the polymer materials is that we can get lots of diffusion for very little light cost, something that doesn't seem very easy to achieve with glass.

BTW,

http://www.poc.com/images/lsd/overvi...ms_graph_b.jpg

That's the graph I was referring to from POC.

Wayne, I agree with your assesement of the fresnel. It is only acting as a condenser, just like a PCX would. The only difference is that a fresnel is very thin and therefore has less light loss, which is why I think they are using it on the Beattie.
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Old January 25th, 2006, 11:43 AM   #88
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Quote:
Originally Posted by Dennis Wood
Wayne, I think the advantage in integrated diffusion/fresnel solutions is that the fresnel is in direct contact with the GG surface, therefore max light redirection. I guess the question is, could you get a DCX that close without distortion?
Yes you can (well a DCX would touch just at 1 point, a PCX would touch on the flat side). Many SLR camera screens do it that way (Nikon for example). Just a PCX touching the screen. I don't think the "touching" is the critical aspect. BTW, the Beattie seems to use a fresnel that acts as a PCX with a focal length of about 150mm.

Besides, there are setups to reduce distortion, like using lens pairs.

I want to try a aspherical lens as a condenser. Anyone with experience with asphericals?
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Old January 25th, 2006, 12:52 PM   #89
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Alain, I've seen that graph...which makes the POC light loss a bit of a mystery. I would assume that no one has actually tried a 10 degree POC in an adapter yet. I believe Dan's test was at 50.
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Old January 25th, 2006, 01:11 PM   #90
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Quote:
Originally Posted by Dennis Wood
Alain, I've seen that graph...which makes the POC light loss a bit of a mystery. I would assume that no one has actually tried a 10 degree POC in an adapter yet. I believe Dan's test was at 50.
I sent a message to POC, and they have not responded, I guess they may have just received quite a few emails from people from the forum :)

If we can figure out if one of their films at some diffusion angle works for us, then we may just buy a roll for all of us ;)
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