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DOF Question - why...
Hi there,.

Why is the Depth of Field effect only visible in the vertical plane and not a circular- radial phenomenon??.

Thanks..

Comments (7)

Laurence Sachs wrote:.

Hi there,.

Why is the Depth of Field effect only visible in the vertical planeand not a circular- radial phenomenon??.

I'm sorry,perhaps I don't understand the question..

Lenses are cylindrically symmetrical & don't know up & down from left & right. What is the radial asymmetry you are implying by "only visible in the vertical plane {vertical direction?}"..

Dave..

Comment #1

Lenses are cylindrically symmetrical & don't know up & down from left& right. What is the radial asymmetry you are implying by "onlyvisible in the vertical plane {vertical direction?}"..

I think the OP wants to know why the DOF does not change from the center of the image to the side (i.e. Circular)...

Comment #2

Yep, what I mean is; why is the range of focus from top to bottom and not from the center(or the focal point) out in a radial direction?.

Thanks..

Comment #3

Laurence Sachs wrote:.

Yep, what I mean is; why is the range of focus from top to bottom andnot from the center(or the focal point) out in a radial direction?.

It isn't. Depth of field is in the 'Z' direction - front to back, near to far...

Comment #4

Here's an image on wikipedia:http://en.wikipedia.org/wiki/Image:Lens3.svghttp://en.wikipedia.org/wiki/Lens_(optics).

If you use the same geometrical ray construction from a different point on the vertical line representing the object plane the point in focus will also fall on the vertical line representing the image plane..

It is a little counter-intuitive, but is an iron-clad result of Euclidian geometry and the way a "thin lens" works (rays parallel to the optic axis go through the focal point and rays through the lens' center are undeviated.).

Real lenses can come close to this ideal..

Hope this helps,Dave..

Comment #5

DOF effects is circular..

Effect you are talking about must be, because usually item in focus point is at about same distance from front lens element as items on right/left or above/below..

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

If focus point is equally far from rest of background you will see equal/circular DOF blurr effect..

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Http://www.stan-pustylnik.smugmug.com..

Comment #6

I think I understand the question even though I do not understand the words you use to ask it..

99.9% of SLR lenses are planar lenses. That means if you take a wide angle shot of a line of dancers on stage they will all be equally in focus (assuming a quality lens) even though those at the extreme end of the line are further away in distance from the lens..

The same would be true in the vertical direction. A wide angle shot of a supermarket shelf will be equally in focus top to bottom..

Why. You already have the answer. They are deliberately made that way. Otherwise you would have significant problems with focus of any long or tall object filling the lens including a human!.

Chris Elliott.

*Nikon* D Eighty + Fifty - Other equipment in Profile.

Http://PlacidoD.Zenfolio.com/..

Comment #7

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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