Example I took at 85mm f/1.4 on APS-C sensor:

enter image description here

  • Do these two pictures are taken from the same exact point? – abetancort May 7 '19 at 22:17

Sometimes a picture, even a crudely drawn one, is worth a thousand words.

enter image description here


That is not entirely true:

You can see better through them because the depth of field (DOF) is shallower. If you focus on the object behind, a wider aperture allows the foreground to be blurred more heavily:

enter image description here

Legend: BG ... background; FG ... foreground.
Photos were made handheld (so framing and focus might nit be 100% accurate), no post-production (except crop and resize).
All photos made at 105mm.

While the sample with the most blurred slats (the first) almost diminishes them, the overall scene became somewhat darker where the blur appears.

  • 2
    Nice observation, but it doesn't really answer the question about why this occurs. – Michael C May 3 '19 at 23:19

The "entrance pupil" is the open aperture you are seeing from the front lens, basically with the diameter f:n (f being the focal length and n being the aperture number). This is basically a disk, every point of which is looking out at any imaged point in the world. The larger this disk is, the more angles are there from which this disk gets a peep at the world. Basically you can draw a cone from the edge of this disk to any point in in-focus distance, and this cone (or its continuation) is how light arrives in the camera for each point on the sensor corresponing to the cone to its in-focus point in the focusing distance. The more an object is out-of-focus, the less is its contribution to any particular cone and the more cones it contributes to. To block an in-focus object point entirely from view, you need to block its entire cone to the entrance pupil. With a large aperture and a close blocking object, only solid objects will do the trick.

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