I played with the Sigma 19mm f/2.8 this evening while digiscoping sparrows through the back window. Dark-eyed Juncos are still around by the dozen. A second Song Sparrow has finally appeared. And, a Fox Sparrow has been kicking around the dirt for the past 3 days! Tree Sparrows continue, as well. I had two birds this evening.
With the 40X W eyepiece the 19mm Sigma shows just the very edges of a vignette circle, so its a nice option for digiscoping. However, I wasn't all that thrilled w/ the sharpness of the images compared w/ the Sigma 28mm f/2.8 that provides a bit more magnification and a bit more punch. Still, these are nice images.
It will be tough to let this digiscoping kit go... Stay tuned.