In my opinion, the article is geometrically correct but uses exaggerated
claims to make his point. Chris has already addressed the girl in the
example so I decided to tackle the B&W image of the man. The claim is
that this image was taken with a 100mm lens at f/2 and "Depth of field
is about 2 inches, maybe less..."
I note first that the image has been cropped since it's not the 2:3
aspect ratio that would be gotten from the author's Canon 1Ds.
Considering the crop, I estimate that the vertical field of view was
about 3 feet and must have been shot from about 9 feet using a 100mm
lens. Using conventional DOF calculations I get a DOF of close to 4
inches. Not the 2 or less he claims. Tight to be sure but not super
critical.
Furthermore, assuming a 3 foot vertical field at 9 feet, the distance
spanned by the center and rightmost focus sensor on a 1Ds would be about
9". A little math tells me that the distance to the plane of focus 9"
off the center line at 9 feet is only 0.37" further. So, by my
estimates, the focus error he speaks of is less than 10% of the
avialable DOF... even at f/2. Hardly the "2-3 inches of focus error
[that] can make the difference between just right and just crap".
I'd give his article a whole lot more credence if he illustrated his
points with precise, comparative pictures. I think I know why he hasn't
done so.
Chuck Norcutt
Chris Barker wrote:
> I suppose that it is an interesting idea, Winsor, but I don't think
> in terms of a plane of focus; so tilting the plane of focus
> (especially the miniscule degree that this chap is describing) is of
> academic interest.
>
> And in the example, the girl's eyes are going to be at the centre of
> focus, with the depth of field chosen to include the other parts of
> the composition that the photographer wishes to be in focus. Again,
> the plane of focus is academic for most people, I suggest.
>
> Chris
> ~~ >-)-
> C M I Barker
> Cambridgeshire, Great Britain.
> +44 (0)7092 251126
> www.threeshoes.co.uk
> homepage.mac.com/zuiko
>
>
> On 9 Apr 2006, at 01:27, Winsor Crosby wrote:
>
>
>>That is not exactly what it says. It does say that using center focus
>>(split image or center sensor) and recomposing is not good. I
>>mentioned it before but this explains it much better:
>>
>>http://visual-vacations.com/Photography/focus-recompose_sucks.htm
>>
>>
>
>
>
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