Dunk ,
Thanks for the reply
I suppose I'm looking for the Holy Grail when it comes to correcting Coma *AND** reducing effective focal length. I have read may posts on Cn and apparently if you make the system faster you get more COMA( physics ??) hence very fast systems have to have a sips system to make them work at all. So I'd be looking for something like this but with a bigger image circle. The search continues.........