Comments on: Look Sharp! http://tleaves.com/2009/10/14/look-sharp/ Creativity x Technology Sat, 17 Mar 2012 05:09:58 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: r. http://tleaves.com/2009/10/14/look-sharp/comment-page-1/#comment-5577 r. Thu, 15 Oct 2009 01:36:46 +0000 http://tleaves.com/?p=2286#comment-5577 I would recommend at least a cursory glance through Merklinger's "The Ins and Outs of Focus", which is out of print now but available as donationware here: http://www.trenholm.org/hmmerk/download.html He goes into a lot of the technical stuff on lenses etc, but only so much to justify a couple of simple rules of thumb. The most useful stuff I found was on how the circle of confusion (or disc of confusion in the subject space) varies on either side of the depth at which things are focussed. The most useful take-home is that a disc of confusion of a given size (say 1/4" in the real world) is going to make way more difference on the near side of your focal plane than the far side, i.e., 1/4" blur on someone's face that is close to you is going to be more "obviously fuzzy" than 1/4" blur on something 20' away. So err on focussing the foreground if you actually want the whole image to look relatively sharp. Unless of course there is a telephone pole and a head. And the hyperfocal distance stuff I think sets a maximum bound on the amount of blur at infinity (disc of confusion upper size bounded by the front element size of your lens) if I remember correctly. Anyway it's worth nerding out over for an evening and then you can promptly forget most of it and stick to the rules of thumb which you summarized above: resolution doesn't matter, final image size does. I would recommend at least a cursory glance through Merklinger’s “The Ins and Outs of Focus”, which is out of print now but available as donationware here: http://www.trenholm.org/hmmerk/download.html

He goes into a lot of the technical stuff on lenses etc, but only so much to justify a couple of simple rules of thumb.

The most useful stuff I found was on how the circle of confusion (or disc of confusion in the subject space) varies on either side of the depth at which things are focussed. The most useful take-home is that a disc of confusion of a given size (say 1/4″ in the real world) is going to make way more difference on the near side of your focal plane than the far side, i.e., 1/4″ blur on someone’s face that is close to you is going to be more “obviously fuzzy” than 1/4″ blur on something 20′ away. So err on focussing the foreground if you actually want the whole image to look relatively sharp. Unless of course there is a telephone pole and a head. And the hyperfocal distance stuff I think sets a maximum bound on the amount of blur at infinity (disc of confusion upper size bounded by the front element size of your lens) if I remember correctly.

Anyway it’s worth nerding out over for an evening and then you can promptly forget most of it and stick to the rules of thumb which you summarized above: resolution doesn’t matter, final image size does.

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