[Shiraz (Ray)]

The CC is essential at this pixel scale Robin (1.17arcsec). In early testing, the image quality was found to drop off due to coma at about the edges of M83 (about 12 arc min across) - see image 1 (no CC and there was also some image plane tilt in this image). The full frame is shown in image 2, downsized to fit the post and displaying significant coma. At the edges of the full 0.89x0.72 degree field of view, coma is horrendous at full resolution - image 3 shows the centre and four corners of a typical sub at native resolution (stretched of course), with an extra panel showing the lower right corner without the RCC1. Huge difference.

The RCC1 has 3 elements and tidies up the coma without appearing to reduce central resolution - something that I have read can be a potential problem with the simpler 2 element CCs on parabolic mirrors.

regards Ray