- Oct 10, 2005
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I'm building some custom theatrical / stage / DJ projectors from LED's, and due to the costs of glass optics I'm looking more and more at Fresnel lenses. The type used for basic magnification, which are rather inexpensive.
What I'm not clear on is if Fresnels use the typical thin lens formulas.
What I need to know is something like; if I have a light source 4" in height, and I have a 10" Fresnel lens with a focal length of 200mm, and if that light source is exactly 200mm on one side of the Fresnel (yes, the ridged side), how far away would you have to be on the other side of the Fresnel for that light source to project 2x as wide (8").
400mm seems a bit too obvious.....
What I'm not clear on is if Fresnels use the typical thin lens formulas.
What I need to know is something like; if I have a light source 4" in height, and I have a 10" Fresnel lens with a focal length of 200mm, and if that light source is exactly 200mm on one side of the Fresnel (yes, the ridged side), how far away would you have to be on the other side of the Fresnel for that light source to project 2x as wide (8").
400mm seems a bit too obvious.....