Fisheye Projection System

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how to make a real video planetarium projector for a low cost

you need

-a computer with stellarium

-a videoprojecteur, typicaly XGA (1024x768), DLP prefered for the contrast. a basic model work well

-an optical system described below

optical principe

place a photo objective (F=50 mm) in front of the lens of videoprojector, image reduces the size of a stamp. just then project the picture through a fisheye it's a type afocal montage. the video projector is absolutely not modified.

witch objective to use ?

a standard F=50 mm F/D 1,4 work very well as image condenser (on 0,55' DLP) , but with a F/D 1,8 the picture may not complete (768 pixels diameter) Fisheye: F=8 mm F/D 3,5 peleng work. Distance between condenser and fisheye = 84 mm . for example, use old objective with screw mount an PVC pipe.

performances

warning ! the PC and Projecteur must using in native resolution, typicaly 800x600 or 1024x768. the diameter of the image measure 600 or 768 pixels

For the best view, stellarium must run in fisheye mode FOV=180° you can use the point mode or magnitude mode (see the 6.4 menu object sizing rule)

use the fisheye diaphragm on F/D=8 for best picture on horizon. With this optical formula, you can get a field of 140 to 150 °, not so bad.

as the DLP projecte an oblique image, optics should not be aligned with the projector, but tilted you need to test alignment to get the best image

so, you can project any other fulldome video

for more information, you can read this page

http://astrosurf.com/lhoumeau/planetariums/en/index.htm

and more examples, in the french version

http://astrosurf.com/lhoumeau/planetariums/fr/index.htm

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