A couple of days ago I did some more  high speed flash work with the 9-microsecond Ultra units.  Here is the result of a double egg explosion.  At first sight it looks o.k. but the more you look at it the more you realise that it is blurry around the edges!  What’s going on here?  I know the flashes are fine as I did all that water drop work just a few weeks back.  I know that it is some sort of distortion as I can take the image into Photoshop, undistort it, and the image sharpens up a LOT.  So what’s changed from the water drop work?  Well for this session I did use the Canon 50mm prime lens instead of the Canon 100mm macro lens I used for the water drops.  But the 50mm prime is one of Canon’s sharpest lenses AND I have used it very successfully for high speed flash work in the past.  So what exactly is going on here??  Two days floating around the subconscious and this morning the answer hits me.  Shooting eggs is a VERY messy business.  This time I was prepared!!  I covered all the gear in cling film and put a cheapo UV filter over the 50mm lens to protect it from the mess.  And there’s your answer.  Had no idea of the repercussions of looking after the lens.  The UV protection filter has introduced all that edge distortion.  Live and learn.  Still very annoying though to have spent all that time and effort on a duff imaging session!