Hi all!
Here is my brief summary on my pentax A 400/5.6.
It is big lens, really good quality, sharp contrasty, great colors to begin with. Many of my shots needed only little PP if any to make it clear and good technically. It has some PF, but that is to be expected. I had to organize my cam bag to be able to carry this around. It is heavy, but I can manage to carry it around and shoot handheld quite easilly. Only gripe is that it is not AF, but that is not this lens fault it is mine. When I nail the focus it is sharp.
I really like 400 mm in wild life shots. Most situations it has enough reach, unlike my 55-300 for example. If I'd have money, my next purchase would be DA*300 and TC. But since I can't afford that, this 400 mm with pricetag around 350€ is enough.
Really, if anyone is looking cheap, sharp way to get in super tele world, give this lens a change. Takes time to get used to it, but it is worth it(you really need good eyesight thou).
All in all great lens, if I intend to take wildlife pictures, this lens will find it's place in my bag. For example my canoing trip I took this, 55-300, 20-35&14/2.8(this pair I'll replace with 16-50 soon). And I could manage all which I wanted to shoot. And that 55-300 just came out of bag now and then.
Alright, that must be it. Great lens for it's prize and age. Had a good time with it. And with you guys!