Peter you are correct that the brighter and not so brighter stars are saturated. All exposures were for 4 min at an ISO of 1600 and at FL of 675mm at f/4.5 so its not surprising. With future blending will do a full spectrum HDR with the 100ED and only use narrow band for the nebula data from the achro.
What is interesting how good the achro is with the neb filter. I think for a $800 OTA the results are much better than expected. I would hate to think how expensive a 150mm diameter F5 APO would be. Assuming it could be built.
I am very pleased at the performance of the achro with 13nm narrow band filters. With careful focusing the star size is comparable to the 100ED actually better at the O3 end of the spectrum due to the larger aperture. Which is what you would expect. I was warned and aware about spherochromatism being a problem but I ignored it.
See here for HA and HDR blended
http://www.iceinspace.com.au/forum/s...ad.php?t=28862
Bert