Cobwebs and Bokeh

As you will have worked out from my previous posts, I’m a big fan of getting things out of focus.  With out of focus images the subject is no longer important; it’s the end result that matters.   One of my Fine Art images shows the exquisite spectra you get when sunlight at just the right angle goes through a cobweb.  I decided to see what a single strand or just a few strands looked like.

I used my OM-1 and OM System 90mm macro lens to give the biggest amount of magnification.   I made sure the background was in shadow to bring out the maximum contrast.  Defocusing the lens made the spectrum much wider than if it was in focus, and it had a delightful tapered shape to it.  There are sharp boundaries between the colours.  It’s a cobweb barcode!

The colours result from interference of light interacting with arrays of tiny, sticky droplets on the web threads, and light going through the transparent thread itself.  The thickness of the thread is close to the wavelength of the light going through it, so it you get thin film diffraction; like you get with a soap bubble.

Taking a few strands that were close to each other gave multiple, wider tapered spectra.  The colours in each spectrum vary hugely, and it’s probably due to the varying angles they are being viewed from.

Defocusing the lens even more made the spectra wider.  Now they look like brightly-coloured amoebae travelling through space.  Spreading the spectra out makes the boundaries between each colour less well-defined, and a bit less saturated.

Just a cobweb in the garden, but look at what happens with the light and the focus just right.