Mono-Monday - Travel - "Travelling Light"

I thought I'd do a bit of lateral thinking for today's Mono-Monday challenge of "Travel".

Light travels at approximately 300,000 kilometres per second in a vacuum, but it slows down in other media. I've shown it here travelling through a casserole dish of water; its speed in water is "only" about 225,000 km/second.

I mixed a drop of milk into the water to make the light beam show up, and if you look closely you can see a condensing lens (+20 dioptres) under the right-side handle of the casserole - I used this to focus the light to a point near the centre of the dish. Ignoring the effect of the glass wall of the dish, the 20 dioptre lens brings the light to a focus at 1/20 of a metre - ie 5cm - from the lens.

It's because light travels at different speeds in different media that we blippers can take photographs. The speed of light in glass is only about 200,000 km/second, and it's the change of speed at the air-glass interfaces which causes the rays of light to bend - and therefore to focus on our camera sensor. Without this effect we could only use pinhole cameras.

Going one step beyond this, of course, our eyes also rely on this effect to focus the image onto our retinas.

(Here endeth the 3rd form physics lecture!! - with apologies to those who know this stuff already!)

The "extra" shows the full setup which I used. You'll note that it included my little LED lights which I usually use for macro work, along with the "Helping Hands" support gadget as on this occasion I couldn't mount the lights on the camera. The books balanced either side of the lights were to shield out stray light.

Many thanks once more to Nickimags888 for hosting Mono-Monday this month.