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Old March 28th, 2008, 05:59 AM   #1
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Compact35 design !

Hi all,

I dreamt last night of a new compact 35mm design, taking advantage of the super small-size of theses new AVCHD camcorder (Panasonic HDC-SD9, Canon HF10, etc). It features non-flipped viewing and recording, only 2 prisms to flip the picture, and therefore should be relatively easy to build.

Here it is !
http://uppix.net/e/0/3/ae6deb66c077d...682802981a.jpg

Last edited by Robin Lobel; March 28th, 2008 at 09:43 AM.
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Old March 28th, 2008, 06:21 AM   #2
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cool but you loose light with 45°prism and adapter need a lot of light :-)
maybe you could use first surface mirror and you have less light lost.
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Old March 28th, 2008, 06:23 AM   #3
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Nice!
Perhaps the next Letus Extreme Micro.
So this came in a dream?
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Old March 28th, 2008, 06:52 AM   #4
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Sure you loose a little light (yet few compared to how much you loose with ground-glass) but less than using 4 prims or 4 mirrors (usual flip-module) !

Prisms were used for the convenience of assembly, but you could use mirrors as well; but I'm not sure it would add more light... Prism provide perfect internal reflection.

Actually it came just before getting asleep, you know this time where you have sudden ideas, but too tired to get off and write it... Then I just prey I remember it when I wake up in the morning.. That was the case ;)
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Old March 28th, 2008, 07:15 AM   #5
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Normal flip only needs to use two prisms of adequate size in porroprism (think binoculars) arrangement. It is what I use and the flip portion of it is fairly compact.

Or for convenience, four smaller right-angled prisms might be back-to-backed with UV optical cement to make two larger right-angled prisms or in the case of the clever people at P+S, an arrangement of three prisms and an adjustable mirror was chosen to do the job.

My understanding is that the light loss of prisms occurs when not all the light which hits the reflective inner surface is bounced. Metalising of the reflective surface apparently helps. There is also apparently a little bit of loss due to reflection from the ingoing surface. This is all hearsay. I have not read it from tech notes or other literature.
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Old March 28th, 2008, 07:22 AM   #6
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I agree, but that's 4 reflections instead of 2 here (I should have said 4 reflect instead of 4 prisms); however the main point of this compact35 is size and ease of assembly. And price ;)
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Old March 29th, 2008, 06:14 AM   #7
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step by step:
http://uppix.net/5/2/1/60ffccb2331ba...1e225460bd.jpg (not the exact same design since ground-glass has been set before the first prism.. but the end result is the same)
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Old March 30th, 2008, 06:41 AM   #8
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new design, even more compact, just 1 reflection, and no ground-glass needed.. Image is seen and recorded in a normal way too (with camcorder's screen flipped down 90 degrees).
http://uppix.net/2/9/1/939e4d7b8dff8...f9e947c1a.html

I have to experiment on light loss (direct projection better or worst than back projection ?), grain (no grain with a white surface ?), and vignetting.

Last edited by Robin Lobel; March 30th, 2008 at 10:14 AM.
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Old March 30th, 2008, 08:44 AM   #9
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Robin.


Removing the groundglass is a dead-end of no advantage except to allow telephoto lenses to be used with a lens-in-camera camcorder in an aerial-image relay path.
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Old March 30th, 2008, 09:41 AM   #10
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Bob: have you watched the drawing ? Groundglass is replaced by a white surface.

Last edited by Robin Lobel; March 30th, 2008 at 10:16 AM.
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Old March 30th, 2008, 11:30 AM   #11
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Robin, does the design with a white surface instead of a ground glass actually work?
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Old March 30th, 2008, 11:57 AM   #12
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It works, but I'm not sure it is very efficient in term of light transmission. Direct projection on paper seems to lose more light than back-projection through ground-glass (EE-S focusing screen). Special surface should be tested, with a more reflective light transmission (maybe like thoses screen used for polarized 3d projection).
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Old March 30th, 2008, 05:37 PM   #13
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wow you just blew my mind with that new design. id was just playing around with an slr lens to see how well it worked, and it definitely does something, just not sure how the light transmission compares to ground glass diffusion, but i imagine it has the potential to be much more adjustable much more easily given the lack of need for diffusion and complete lack of aerial image.
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Old March 30th, 2008, 06:54 PM   #14
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Robin.


Your design eliminates several stages of internal reflection which can only be helpful, however you still have four stages of air-to-glass or glass-to-air and you are trying to come back out to camera through an inclined surface.

I won't burden you with my opinion of surface reflection as a method of image presentation to the camcorder.

You are an experimenter and that is good. Sometimes designs which have been discarded are picked up again by a new mind, one critical element changed or added and a revolutionary step forward occurs.

Last edited by Bob Hart; March 30th, 2008 at 06:54 PM. Reason: error
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Old March 30th, 2008, 07:28 PM   #15
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bob, i would be interested to hear what you have to say about the surface reflection method. or perhaps there is a thread that covers it i have missed? it certainly makes sense that it has been attempted before, so im just surprised i havent heard more about it. but id definitely be interested in whatever you know about it and about why it the idea has been passed over in the past.
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