I've liked this lens for a long time and have posted favourably about it before.
Yesterday, bored by the continuous bad weather, I discovered I could shoot from inside the back porch of our house (ie. indoors, out of the rain) and still get a usable image size of groups of birds interacting (squabbling) on our feeders.
I made quite a number of shots and the attachment is a 100% crop from one of them - the 400mm f5.6 at f8, 1/200sec and 1000iso. The image has been sharpened but no NR applied. I know modern telephotos are superb, but I think this is an excellent result from a 30-year-old lens which you can pick up for few hundred dollars.