This was a response to TCampbell but not sure how to actually make a reply a reply to a post —
Thank you for all this — really comprehensive and exactly what I was hoping to learn. Thank you so much.
One follow-up: one key part of what I am trying to achieve (which I should have been more clear about) is bokeh at dusk and night — and the distant lights turning into the translucent/opaque circles.
Would you alter your opinion at all to achieve this effect?
Again thanks for your input.
@TCampbell
Esteemed Contributor wrote:
One last point...
This one can be a bit confusing but... I may as well adress it because you're bound to run into this.
You'll occasionally find either an article or a person who will say that the size of the sensor also contributes to the amount of blur.
This is "sort of" true.
Technically in absolute terms, its not true... but there's a side-effect. When a camera has a larger sensor (the dimensions of the digital sensor are larger in one camera than in another) then that camera will technically have a wider "angle of view" as compared to when that same lens is used on a camera with a smaller sensor.
But photographers have a composition in mind for how they want to frame a subject. And since the angle of view is wider, it means they can get closer to the subject to still get the framing they want.
BECAUSE they are closer... they've decreased the depth of field and increased the amount of background blur.
The reverse... using a camera with a smaller sensor to frame a subject, means they'll need to take a few steps back to get the equivalent compositon ... thereby increasing the focused distance to the subject. That increase distance also increases the depth of field and decreases the amount of background blur.
So the physics of the lens are that the focal length is the focal length is the focal length ... and the amount of blur you get from a lens of a given focal length and a given focal ratio at a given focused distance DOES NOT CHANGE just because you changed the size of the camera sensor. But it WILL change the angle of view.
But thre reality is... the photographer will now behave differently because the angle of view changed (by standing either nearer or farhter) and that DISTANCE change will alter the depth of field.
Consequently, you'll hear that cameras with larger sensors produce shallower depth of field and stronger background blur. Strictly speaking it isn't the sensor size... but the fact that the photographer is able to position the camera closer to the subject which causes that change.
But the net-effect is ... yeah... you'll get more blur shooting with a full frame camerra (because when you used the crop-frame camera you didn't have the option to position the camera closer without cutting out some of what you wanted to capture.)
