75mm lens holder
thingiverse
Holder for 75mm aspheric plano-convex condenser lens, "75mm-LED-convex-lens-Glass-condenser" ebay item 131781069708. These are I assume made for car headlights; it works perfectly well as a LED collimator. The OD of the lens is precisely 75 mm but there is a flat rim so the optically useful diameter is about 70 mm. Focal length is exactly 50 mm, making the lens f/0.7 (calculated). The first photo shows it next to a similar holder for a 50mm condenser lens: http://www.thingiverse.com/thing:318346. If you print two of these, you can sandwich the lens between them to create a square frame.
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