Solar Shadow Rings - 29th December

The sun hangs low among the trees and rooftops around mid winter and this if often more of a hinderance than anything else, however today I noticed a very curious effect I have never seen before.  I could see a strange ring patter created by the branches rapidly appearing and disappearing on the laptop screen.  I initially thought this was similar to when there is an eclipse in progress and light shining through the leaves on the trees creates crescent shaped shadows, however I quickly dismissed this as there are no leaves this time of year, and if a pin hole projection effect was happening then there would be circles projected not annuli as in the animation above.  Then it dawned on me, the Coronado SM40 etalons I use have a central obstruction that project a shadow on the image of the projected circular disks through the trees.  Well, that's my theory anyway, if anyone knows any other possibilities please feel free to comment on this post.  Either way i'm happy with the result and have ended up photographing something i've never seen before!