Quote:
Originally Posted by yelvertoft
I'm not surprised at all that the straws are needed. Stephen, imagine the straws as acting like a series of singlemode optical fibers, without the straws it would be more like one large bit of multimode. The the light will bounce down the tube giving a wider dispersion as it leaves the end.
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Duncan that makes a lot of sense but I am thinking multimode light would quickly diminish leaving only a singlemode beam if the length is beyond a critical dimension for this to occur. Critical length depends on diameter of tube and with a party straw this length is achieved as their length must be 40 times their diameter( approx 5mm dia and 200mm length). If the critical length ratio is 40:1 then my 80mm diameter snoot would need to be 3.2m
to give the same result as one party straw.
Here is my photo using long 500mm snoot toward the label of champagne bottle. I recall it be very difficult to aim as the beam was direct.
http://www.worldphotographyforum.com...hp?photo=11266