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Old 8th May 2012
Kiwi Paul
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Diffraction explained

Here's 3 links to articles explaining how diffraction affects photography using digital cameras. hopefully this will clear up some of the myths and confusion about the subject.




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Old 8th May 2012
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Re: Diffraction explained

This was discussed over on DPNow and I found the whole thing very interesting, so I thought I'd test a long held belief...

The idea of illuminating the subject with a blue light to reduce the effect of diffraction for use in a specialised style of B&W photography.

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

White Light (Flash)

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.

From a practical viewpoint, this is useless because controling the colour of the light is rarely possible and it has huge effects on the final image, depending on how the subject absorbs and reflects the different coloured light.

As we all know when using filters on the lens for B&W photography, they alter the contrast and other aspects of the image, so again not a practical solution.

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

We often repeat the mistakes we most enjoy...
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Old 9th May 2012
Kiwi Paul
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Re: Diffraction explained

There is one area that I'm still a bit unclear on and that is whether or not 2 different sized sensors display the same image detail if the higher megapixel sensor is past its diffraction limit.
For example lets say we have a camera with a 10 MP sensor and one with a 16MP sensor and we use an aperture of say f11. The 16Mp camera is now into diffraction but the 10Mp sensor is just outside it's diffraction limit, if we then resize both images so they are the same size and compare them, does the 16Mp image look softer due to diffraction or do they look the same as the 10Mp camera doesn't have the resolution to show the lens diffraction yet. My guess is they both will look the same (all else being equal), I'd like to test this out but only have one camera so can't.
If the IQ is the same in the example I've given then using sensors with higher pixel count does make sense in that there is no disadvantage and plenty of advantages but if the IQ is lower in the diffraction limited scenario then as the pixel count goes up we are limiting ourselves to lenses that need very wide apertures.

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Old 9th May 2012
Kiwi Paul
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Re: Diffraction explained

Interesting test Graham, shows the effect of colour, diffraction and aperture very well.

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