Confused of Oxfordshire

[Keithw]

I went for a walk in the Chilterns on Boxing Day and failed to take any photos that could be regarded as even half-decent. Walking back to the car I looked up and saw this plane:



So I swung the GX-10 striaght up and clicked. I had thought of asking whether we were on a main flight path or just a branch line but decided that that it wasn't as amusing as I hoped so didn't.

But when looking at he photo I got to wondering, and the more I wondered the more confused I got. The question is - why can I see the whole of the wing when ythere is a branch in the way?

A closer look at the plane:




shows the branch. Here is a 100% crop of the wing:



and while there is a bit of shadow where the branch is, I can still see the wing. Or can I? And if I can, why? Has the light bent around the branch? Or is that against the laws of physics? Is it just an optical illusion or is my brain playing tricks?

Too many questions and not enough answers. I'm confused!

[Alan T]

What was the shutter speed? It should be in the image files's exif data.

Here a guess, atentative theory:Maybe the twigs moved sufficiently to allow a mostly clear view of each bit of the plane in the time the shutter was open. The apparent movement of the plane is very, very small, but that of the twig, even if a very small distance, being very close to the lens, was a relatively large part of the field of view in those few milliseconds.

[NonEntity1]

My guess would be that since the lens is wider than the branch it gathered light "around" the branch. In other words, the top of the lens could "see" some of the wing and the bottom of the lens could "see" the other portion of the wing. Since you werefocusing on the plane the branch is blurred out and you can see through it.

Tim

[bilybianca]

Tim is right, or nearly. The top of the lens, and the bottom of the lens, gathered the light that was behind the branch as seen from the middle of the lens. It's just a question of "front bokeh", out of focus blurring in front of the focus plane. (The focus plane is where the airplane is!:-))

You can use it to blur out a fence at the zoo if there is a long enough distance between the fence and the subject, and if you hold your camera near enough to the fence.The larger aperture you use, the less you see of the fence (or as in this case the branches).

Kjell

[Keithw]

Thanks guys.

I think I understand what you are saying although if I think about it too much my brain begins to bleed :G

Happy new year folks!

[Alan T]

Keithw wrote:

....I think about it too much my brain begins to bleed

Nonentity1 and billybianca are right & I'm wrong. It's not that hard if I can understand it.

Just draw a diagram of a lens, a distant object & a near object covering just part of the lens and you'll be able to see that from each point of the distant object you can draw rays in straight lines to the lens that miss the near object altogether, hit the lens, and are bent to hit the right point on the sensor. All these will form an image of that point of the distant object, slightly dimmed because a little less light got there, some of it having hit the twig. The twig is out of focus, just as they say, smudged in the extreme.

You can tell I'm just a stupid chemist and not a physicist. Though I've had to explain lots of chemistry to physicists in my time!

Fine piece of experimental observation by the way! Have you considered a career in science? Oh, no, scientist folk like me aren't needed any more; it's financial instruments and trading that are going to save the world, aren't they?