[ozstronomer (Geoff)]

Hi all

I had the chance to find 3 hours of clear sky last weekend and wanted to try out a canon 50mm lens I've had for a while but never really used.

I set up to take a wide field of Orion with my Canon 20d(modded) guided on top of a WO 110 refractor and meade dsi pro. Captured with Nebulosity, guided with PHD

After taking 10 x 3min images I noticed severe pincushioning at each corner,the centre looks ok. The lens was set at f2.8

Can anyone suggest how to adjust this lens to make it flatter. I thought these 50mm lenses were ok for Astrophotography, but I maybe mistaken.