If you'd like shutter control, try ShutterMagic. You can use it for light painting too! Here's a sample when I was testing it with really slow shutter speeds. I had to make sure I was writing in reverse.
Correct me if I'm wrong, but I think you can not improve a lens by a software. So any improvement made by an app is something you can do yourself after picture taken, via photoshop or other similar program.