75 pence DIY Snoot

[Canis Vulpes]

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.

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

[Don Hoey]

Originally Posted by Canis Vulpes

.......... 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.

Educated under a flat top thorn tree on the plains of Africa, so that lot has gone right over my head.

Don

[Canis Vulpes]

Singlemode fibre optics employs a single beam which transmits parallel to the fibre internally. i.e. direct light.

Multimode employs lots of different angles and light frequencies that bounce off the internal sides of the optical fibre i.e dispersed light. Multimode used thicker optical fibre cable.

At a certain length multimode operation should expire leaving only direct light and return to singlemode albeit reduced power.

The party straws no doubt will operate like lots of single mode fibres and allow for a shorter snoot.

Please find below diagram showing single and multimode fibres (its in french)

I'll get me some straws and do my own experiment.

[Don Hoey]

Thanks for that. A bit worried when I read it was in French not Swahilli.
Makes sense now.

Don

[Canis Vulpes]

Can you believe there were NO party straws at the supermarket this afternoon. Either that or my lady forgot

Still she has another two tubes of pringles for me to create the super snoot to test length and straws.

[Lello]

I have bought the pringles (just need to eat them now) and the straws, so just waiting for instructions on what sort of length to cut them

[Don Hoey]

Lello,

Try the straws full length first. I guess the Pringles tin being of larger diameter than my cardboard tube will project a larger beam for the same length of straw as in mine.

I had little choice over trimming mine as they are the ones that bend over at the end. So the trim point was just in front of the bendy bit.

Looks like you will beat Foxy to this one.

Don

[Lello]

The pringles have to be eaten first, and I'm the only one in the house that eats them, Might take a few days, Unless I put some in jiffy bags and distribute them among the WPF members

[yelvertoft]

Originally Posted by Lello

The pringles have to be eaten first, and I'm the only one in the house that eats them, Might take a few days....

Days!!!! To eat a tube of Pringles?

Anyone found silvered straws on sale? I've seen them in pubs and bars, but never in the shops. Might make a difference.

[Don Hoey]

Thanks to Foxy's chart on light posted yesterday, I had a thought, and as I had failed on the zoom snoot front, although zooming can be achieved by moving the flash relative to subject. Decided to try a different tack.

I made a thin slice of metal with a 20mm hole so like a large washer. ( I know, but I do not have any black card to use instead ) This made the equivalent of the old fashioned Waterhouse Stop.

Placed over the front of the 5" length snoot with straws, the object was to see if I could reduce the size of the outputted light circle. It works and results in the attatched graphic.

Knowing Mark has made rectangular units, this principle would allow moving from rectangular through square to circular light pattern with different shaped cut cards.

Don