Lightning strikes twice

Started Aug 7, 2012 | Discussions thread
falconeyes
Senior MemberPosts: 1,001
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A physicist's analysis of reflection
In reply to efg40, Aug 8, 2012

I've browsed thru the thread here and it has quite an entertainment value.

While it is true that lightnings can strike multiple times thru the same ionized channel which additionally can have a drift, this is not what has happened here.

I analyzed the image via overlay:

The 3D-look to the middle channel is the result of the secondary channel being an EXACT copy of the primary channel, offset as marked by the red line. The duplicated secondary channel fill parts of the primary channel giving it this 3D look, meaning it is an exact copy.

The problem with this is that this means that the secondary channel is not reaching earth! It is not a real object, just an optical illusion. The wind speed argument already hinted at that.

Moreover, the optical effect is easily explained: The lightning stroke is so bright that it overblows the sensor by several orders of magnitudes, many EV stops. Therefore, even the faintest reflections within the optical system become visible, as well as even minor chromatic aberration.

And there is at least one unavoidable reflection in any system: Between the sensor's protective glass inner surface and the Bayer-AA filter (or IR cut filter) outer glass surface. The offset should be larger towards the borders of the image which may be a reason why it is more pronounced in the second lightning.

As a rule of thumb, such reflections often occur at the same time as CA becomes overly strong. It is a known phenomenon from night photography with overblown light sources towards the borders of an image.

Kind regards,
Falk

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