Infinite depth of field (ii)

For those of you following my blog, this shows what I generally hate most about point and shoot cameras – Infinite depth of field.

However, in this instance, perhaps I forgive them this failing. But the numbers don’t lie – 1/500 @ f5. What I really need is not f 5 – I want an an f0.5 lens on these cameras for subject separation possibilities. Please, pretty please, fit them with really fast lenses so they are of more real utility.

For those not familiar with DoF issues on a P&S camera, I hope I can shed some light on the subject of DoF in a half intelligent manner.

Depth of field is related directly to focal length of the lens, as well as the aperture used (and also to the subject distance, but I won’t worry about that here for clarity). Very wide angle lenses for 35mm cameras – 20mm or so – provide great depth of field even at fairly wide apertures. The focal length of a lens for a camera with a sensor size of 5 by 7 millimeters or so as in a P&S camera drops enormously, down to 6mm for a 35 mm equivalent view, or less for a wider one. It is still an incredibly short lens, although the senor size means it appears to have a normal field of view, but the very same physics that dictate DoF for 35mm cameras means that at these short focal lengths, just about everything is in focus at just about all lens settings, irrespective of the aperture.

Hence my hatred of P&S cameras – selective focus is just about impossible, except at long telephoto focal lengths. In addition, even at its widest setting, a 35mm FoV equivalent, there is considerable barrel distortion. I used the “distort” filter in Photoshop to straighten this up or there would be a curved horizon where there shouldn’t, at a setting of about 4. This is pretty poor performance, and although easily fixed it shouldn’t be there in the first place.

With 35mm sensor sizes, optical diffraction starts to set in at about f11 or so depending on the sensor pixel size, and image quality then starts to degrade. This is true from about f5.6 on a P&S, so chasing a really small aperture is self-defeating with these cameras.

Footnote – This picture actually made it to no. 9 in Flickr’s Interestingness rating on 6 April 2010, and so onto the front page. I find it hard to believe, but here’s proof:

6 days on – 1600 views, 78 favourites and 45 comments. I’m humbled, especially by this camera.


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