On Jul 13, 2008, at 4:29 PM, Tom Piwowar wrote:
Actually, autofocus depends upon having areas of substantially
differing contrast adjacent to each other within the focusing area.
Cameras will vary, but you try it on a field of sharply drawn
horizontal
lines and see what happens.
I have done that a number of times when using a specially designed
template for determining the amount of back/front focus, if any, that
exists in a given camera. Indeed, that system for determining any
back/front focus issues works with any camera, and all of the lines
used in that system are horizontal.
http://focustestchart.com/focus21.pdf
In your example, and with most decent contemporary cameras, I
think that you will find that it is primarily the contrast between
the drawn line and the background that provides for the ability to
autofocus, and not the orientation of those lines. Having said that,
early autofocus systems did mostly rely on horizontal areas of
contrast to achieve autofocus because their sensors were all
vertically oriented. However, other areas of contrast at different
angles could still provide for readings, but perhaps not as
accurately. These days, most decent cameras, SLR or otherwise, have
both vertical and horizontal sensors. Some have them at 45 degrees.
Steve
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