Even zoomed in, they are true cryptic wonders.
I come across these moths beginning in late April/early May, but I couldn't resist this shot on an August afternoon.
This photo taken June 4, 2015 shows how variable their color can be. The moth in the middle shows form "carbonaria", a melanic form of this species. It's the first time I've seen one so dark. The one up top seems to be somewhere between the two below it, colorwise.
This, by the way, is how they landed on the sheet! (I did flick a couple of little moths out of the frame, though...)