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Old January 8th, 2004, 09:10 PM   #91
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Late to the game here.

sampling frequency (Niquist) theory says you have to sample at 2X the frequency to capture all the detail. However you may still capture multiples that coincide with pixel frequency.

So the comment about DV not having enough resolution to capture the full details of the diffuser is correct. Also because the width of each line is so much less than the width of a pixel, I think it's unlikely that artifacting of coincident multiples (like a morray effect) would happen.

I've lately built and automated film recorder and have been working out my video production chain.

My camera is a DVCPRO25 which has a removable lens and I'm already doing a lot in post to get things right for xfer to film so all the optics besides the diffuser are out of the question for me.

Having just found this thread and Agus' thread. I think static is the way to go for a production environment friendly piece of equipment. Not to mention I don't want to have an injunction slapped on me for shooting a movie with someone elses intellectual property.

I definately plan to build one of these babies.

Thanks to everyone who got in early.
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Old January 8th, 2004, 10:35 PM   #92
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Can someone explain to me what the degrees mean in reference to this holographic glass? Does it mean the glass has to be slanted at that angle when put in your design? Or does it just mean that something in the glass itself (the granule's?) is slanded at that angle?

thanks
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Old January 8th, 2004, 11:17 PM   #93
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I've been trying for a while now to find information clarifying exactly what Mike just asked. All I can find is information on "scattering angle." Diffusion and scattering basically mean the same thing, so what I think is that the angle of diffusion represents the amount (specifically angle) that the visible area of image is projected onto the diffuser. Basically, when you look at the back of a lens, you will see only a small circle of the image coming through the lens. This is because you can only see what is directly in your line of sight, directly in front of your eye. As you move your eye in a linear motion side to side, still remaining the same distance from the lens, you will see different areas of the image coming through the lens. The diffuser takes the infinitely different "angles of sight" and concentrates them on one area - the ground glass/diffusion surface. The angle of diffusion causes a variation in how much is being diffused.
Okay, now that I've confused everyone, including myself, here's a link... http://topcontechnotes.home.att.net/...tem/page4.html.
Hopefully, someone has found some other information regarding this question that either proves or disproves my theory.
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Old January 8th, 2004, 11:38 PM   #94
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My understanding of this term (and most likely to be correct) is it's the angle of the viewable area. This measurement is also used for LCD screens and projector screens. When you are within the specified angle in front of the screen, you will see an acceptable image, if you are outside of the area defined by the angle, you will not see the image correctly (too dark etc.), and the reason for that is light are not scattered (enough) to the areas outside the specified angle.

For some applications, you want to have a wider view angle for the screen, for LCD and projector screen etc. so that more people can see the image.

So the holographic diffusers can control where to diffuse the light and control the area where it targets to.
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Old January 9th, 2004, 12:00 AM   #95
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That makes sense. Which would indicate, like you plan to experiment, that a smaller angle of view would provide better results due to the camcorder lens always remaining at the same "straight shot" angle. Am I understanding correctly?
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Old January 9th, 2004, 01:43 AM   #96
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That's exactly what I think.
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Old January 9th, 2004, 11:54 AM   #97
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If I have understood the formula for the angle of diffusion given on the POC website correctly, the amazing thing about the holographic diffusers is that they diffuse off-axis rays less than on-axis rays. For example, with a 10 degree diffuser, a ray hitting the diffuser at 40 deg to the normal will only be diffused to a 2 deg cone. This appears to explain the lack of hot-spots and it also suggests that a small-angle diffuser will work if the rest of the system is correct.

I'm attempting to have a discussion on this with the folks at POC (they make the diffusers sold by Edmunds et al) but haven't had much luck so far. I think that I'll end up getting the 10 degree sheet and testing it myself. As I've already mentioned, my current setup works without a diffuser as far as even illumination and full frame viewing goes, but it needs a diffuser to form a single image plane instead of a 3-D aerial image.

Best,
Helen
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Old January 10th, 2004, 08:47 AM   #98
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Thank you for answering that question. Makes sense now. Sounds like it should work out great. I'm excited to see the results.

I have a couple other question though:

http://f2.pg.photos.yahoo.com/ph/lou...m=DSC00142.jpg

The prism at the top of the image. What kind is that and what will it do? Is it the same type speculated to be used in the movietube design where it will flip the image but the camera needs to be mounted at a 45 degree angle to it? If so that doesn't sound that bad. Might even be kind of nice ergonomically to have the camera slanted. At least for my camera which is a vertical design and could use some extra space at the bottom.
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Old January 10th, 2004, 10:00 AM   #99
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The prism at the top of the page with a smokey black surface is called a pentaprism. Basically it reflects the image 90 degrees but doesn't invert or revert the image (utilizing two reflective surfaces to accomplish the 90 degree angle). That's what we're using to make the camcorder located at a horizontal angle.
Not much is known about the MOVIEtube yet, not even the price or availability. My theory, however, is that they use a Schmidt prism (http://www.edmundoptics.com/IOD/Disp...Productid=2430) which inverts and reverts the image (which is what we need), yet deviates it 45 degrees. That means the camcorder would have to be located at a 45 degree angle in order to properly capture the image. The prism might even provide the required distance from the 35mm lens to the diffuser surface which would make the adaptor much shorter. The camcorder lens could be right up to the diffuser, almost as close as a filter? At least that's my theory.
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Old January 10th, 2004, 10:16 AM   #100
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Here's a neat link that has drawings, characteristics, and names of many different types and variations of prisms.
http://www.tecplusplus.de/ManualLu/prisms.htm

Ultimately, the mirror/roof pentaprism would be a great solution. Right now, I'm using the prism I pulled out of an old SLR camera. Unfortunately, probably to save space, the "roof" is right on top of the "floor" surface. Many of the drawings on the internet show a distance between the two surfaces (like a house with walls), however mine only has a small distance (like a roof on the ground). This will still work fine, but I have to place the prism further away from the diffuser in order for the camcorder to zoom in far enough to capture the entire frame but not be cut off by the roof. That makes my adapter really tall, which I'd hoped to avoid. Maybe SurplusShed will get in a shipment of roof pentaprisms exactly like we need. Here's hopin' :).
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Old January 11th, 2004, 02:22 AM   #101
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great link

nicholi,

just great link!
i was surfing on the net just to find single place with everythig about prisms explained and showed. i already have tons of different jpgs. from many places, but this one RULES! thank you for that.

filip

p.s.
did you tryed to "construct" something with sowtware mentioned there? how it looks?
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Old January 11th, 2004, 02:29 AM   #102
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free software for prism "construction" ?

does anyone knows about free software for prism "construction" and virtual testing?
i mean - i'm not expert on optics, but if that kind of software exist - then (i suppose) is much, much more simpler to make your own construction of static adapter. i'm confused when i'm checking different prism - how and why certain picture will look. will it be reversal, left-to right or what...

any links are helpful.

filip

p.s.
i checked the link mentioned by nicholi and there is demo etc. but with some options disabled... :(
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Old January 12th, 2004, 02:33 AM   #103
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Anamorphic prism

How about working this in...

http://www.optima-prec.com/prism.htm


Great work guys! I think what you're doing is awesome. I come from a still photography background and also thought Boss Screen might work, but the temperature would be an issue. I have a DVX100 and I intend on using stacked achromatic diopters. Any word on exact prism sizes and sizes of the hologram material? What should I get for a 72mm lense? All the best in your endeavors. I'm eager to try this myself.

Best regards,Mike
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Old January 12th, 2004, 02:45 AM   #104
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Frank....

I'm a bit of a neophyte when it comes to prisms. How does an anamorphic prism constructed to regulate laser beams correlate to prisms that reflect pictures? Is there a difference? Does it control the light better than say a holo-difuser with a 10 degree light scatter? It's anamorphic, so, does that mean it captures or transfers a larger picture? I'm using the DVX100 as well.
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Old January 12th, 2004, 10:08 AM   #105
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Just throwing fat on the fire...

You know what Dean, I'm not well-versed in this either. Maybe it doesn't need to invert, just project an anamorphic image.( if that's what this prism even does.) I'll try and contact the company today and find out. Best- Frank/ Mike, actually my middle name is Mike and that's what everyone calls me and for some reason, I put Frank as my user name. But I answer to either and I've certainly answered to worse. :)
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