I know I'm not the world's best photographer, but I really don't think I'm as bad as some of my recent pictures make out. They just don't seem sharp at all even after processing them in Photoshop. I really need to check out the focusing on my Nikon D90 camera because what seems pin sharp in the viewfinder rarely looks the same on the computer.
I've always suspected that my Sigma 50-500mm zoom lens wasn't as sharp as it could be. I know you only get what you pay for but it was still quite expensive for a hobby and I really can't afford a Nikon prime lens with the same range. I nearly always use this lens fully extended because that's what you buy a lens of this size for, isn't it? I'd say 95% of what I shoot is rubbish and even the 5% of good shots are seldom crystal clear. The lens is generally OK with closer or larger objects than birds.
So I'm going to do some testing with a few focus charts I've printed off the internet and I'm also going to try my lens on another Nikon camera body (my daughter Cathy has a D3100). If I can prove anything from these tests I'll be looking at buying another lens (probably the new Sigma 50-500mm with OS) or perhaps having my camera serviced. Watch this space for further developments.