Next mini-book on ray tracing

I am almost done with the next (and probably last) mini-book on ray tracing.   It will be free for the first five days at the kindle store (probably sometime this week) so do not buy it -- there may be a short time when Amazon hasn't made it free yet.   The associated web site will be at in1weekend.com just like the first book.   This the the image with the features added:

Final image for Ray Tracing: the Next Week

The features added are solid texture, image texture, participating medium, motion blur, instancing, and BVH.   I decided not to add explicit direct light so it's still brute force path tracing (thus the caustic is implicit).