It's technically a "prime" (fixed focal length), 105mm. I have it on a DX body which is a 1.5x crop factor, so that's a field of view equivalent to roughly 157mm focal length on a full-frame body. At 157mm equivalent, it is a little bit on the long side, but it has VR which helps a lot.
There's no focus stacking, that's something I would like to try though but it seems hard to ensure ideal conditions to get stack-worthy frames in the field. That particular frame was shot at f/22 and the fly was sideways which helped, plus I cropped in a fair bit too. Here's a similar frame I captured but at f/16, you can see the eye detail is a little better but much of the rest is not very sharp: