Both images show 12.5 arc-minute-square views. For the 20D that is the full height of its frame, so only the sides have been cropped. For the 1Ds I took a central crop with the requisite Field of View. Problem with Omega Centauri is that it lies well into the murky muck of light pollution at my home. In fact the skyfog around it measured at Visual Limiting Magnitude 1 ! And it was only some 18 degrees above the horizon. Thanks be to Go-To computerisation, otherwise I would not have any hopes of ever finding it. The skyfog was so bad that I could not get rid of colour smears, and I suspect that the low altitude also added atmospheric dispersion coloration to the stars; thus the monochromatic presentation. I had switched to the bigger frame Canon 1Ds, since Omega Centauri subtends a larger angle than M13 and I was afraid that it may not fit into the 20D frame. However, with such bad light pollution I should not have bothered. I managed to capture only the central portion. M13 is the largest (as seen from Earth) globular cluster of the northern hemisphere, but Omega Centauri is the king of the south. Both images were shot unguided on a CGE mount.
An unexpected effect: Both of these globulars had been shot with North to one side. When I rotated them to have North Up, I immediately noticed that they were quite oblate, both squashed in the North/South direction, sort of Jupiter-like. Same rotational cause?