Weird Corners... What happened to my Sky90?

Sky90 with F4.5 reducer/flattener, 1min x 10, unguided, 5DII modified

Full Image:

Centre crop

 Top right, bottom right, top left, bottom left

To demonstrate the problem this is an image taken in 2008, same scope and reducer, Mamiya 645 E200, manually guided 1 hour.

Is this a yearly blog or something?

I have been pretty frustrated not grabbing chances to go out when weather is good. I don't know what happened to my lazy bones...

Anyway, I have been to a few places in 2012, including A few countries in Europe as well as a popular site for Hong Kong people in China.

Haven't been able to do autoguiding yet, but actively looking for good weather to try it out. The following are the pictures I took in 2012...