cdo221 wrote in post #12025333
Excellent write up. I had a question regarding bokeh. I heard it depends only on aperture and your distance from the subject. So if you are far away but zoom in for the same framing as standing close zoomed out (ignoring the change in the perspective and size of the background stuff and looking at just the subject), will the background be the same amount of blur? Of coures the background will be different b/c of perspective but what abou the bokeh?
First, let's get terminology correct -- not because I am anal compulsive about terminology, but only to make sure we start with a common foundation of mutual understanding:
Depth of field (DOF) is the zone of focus in which they eye perceives small little circles, which are below a certain size, to be 'points'...the blur circles are small enough to fool the eye and brain into thinking 'sharp'. This is affected by FL, aperture, how large the image is and how far you are from the image as you view it
Out of focus background is everything behind the DOF zone, where the out of focus circles large enough to be perceived by the brain as 'blurry'. This is affected by FL, aperture, how large the image is and how far you are from the image as you view it.
Bokeh is a characteristic of the optical design of the lens and does not increase/decrease with changes in aperture, or how large the image is and how far you are from the image as you view it. Mirror lenses are usually typified by the unpleasant donut rings for out of focus highlight areas, bad bokeh. Bokeh is qualified as 'pleasing bokeh' or 'unpleasant bokeh' (or somewhere in between) and is not typically quantified. Bokeh characteristics can be different in a lens wide open vs. the same one stopped down, but it is the quality which changes, not the quantity of bokeh. This articles shows different bokeh in different lenses at f/4, and again at f/11, to illustrate what I just stated.
Just as DOF increases with smaller aperture (larger f/number), the Out-of-Focus background blur also decreases (gets less blurry) with smaller aperture. To illustrate, 50mm at f/1.8 vs. 50mm at f/4...
The amount of background blur does change with FL, as was illustrated in the early posts of this thread (Post 3).
does not get different unless camera position changes
! Perspective does not change with FL or aperture, it only changes when the camera position changes. (Post 4)