Playing with Diffraction and coloured light

[Graham_of_Rainham]

I finally got round to testing the idea of illuminating the subject with a blue light to reduce the effect of diffraction.

I pressed to service my ever co-operative muse for this crude set of tests



With the camera set to f/22 and manual focus, I took 3 pictures.
The one above, with the bare flash, one with a Red gel over the flash and another with a Blue gel





I then removed the colour from the RAW files, examined them and cropped an area which I think best shows the effect.

RED Light


Blue Light


The filters used are very saturated "effects" filters and beyond any colours that you would get from natural light, but serve to show how the longer wavelength of the red light is diffracted more than the short wavelength blue light.

As we all know when using filters on the lens for B&W photography, they alter the contrast and other aspects of the final image, depending on how the subject absorbs and reflects the different coloured light.

What is interesting is just how good an Olympus 14-42 kit lens is at f/22

[Phill D]

Re: Playing with Diffraction and coloured light

Graham that's amaizing, obvious when I come to think of the physics but I hadn't before and your demo shows it up so well. How about showing the standard shot in B&W just to compare with the converted blue one. I guess it would be difficult to see the differences but I'm just curious.

[Graham_of_Rainham]

Re: Playing with Diffraction and coloured light

Interesting that you ask...

Given that the flash is illuminating at 5500K to 6000K and that this is much closer to the blue end than the 2000K of the red light, the diffraction that can be seen is visually closer to the blue than the red. I used Faststone Image Viewer to do a side-by-side-by-side comparison and the results are quite conclusive.

Bare Flash (white) light


I really miss my days in the labs, experimenting with things