Hi Geof
Tend to agree with Paul. Although the distortion of the energy spot in the centre is a bit odd, almost suggestive of pinched optics, however the donut looks pretty symmetrical. Did you test with a good laser to see if return beam hits the centre spot? The following thread on Cloudynights might shed further light:
http://www.cloudynights.com/ubbthrea...7/Main/6544222
Ted