[Shiraz (Ray)]

good question Rolf. Best quality optics is always worth having, but your question is - is top quality necessary when the atmosphere dominates?.

FWIW, my current thinking:
1. highest possible quality is required for visual use - we are very good at seeing anomalies and can pick up the effects of relatively minor aberrations very efficiently (particularly if we are unfortunate enough to know what to look for). Assume that is why people still pay big bucks for tiny but perfect refractors for visual use.
2. system requirements dominate for planetary - collecting lots of photons is a large part of the game and a big, but less-than-perfect optic may outperform a smaller perfect one, since it allows higher frame rates to help with seeing problems. Other issues such as thermal management and mirror cell design for equatorial mounting are also vitally important. I have only once found conditions good enough to test the limits of my GSO 12 inch optics over a full year of planetary imaging - but it would still be nice to have top quality optics though, just in case that mythical perfect night comes along.
3. optical quality is much less important for deep space imaging. The atmophere limits the resolution much more than the optical system and you can correct for many defects such as lower contrast etc in post processing - which explains why RC systems are popular, even though they start out with low Strehl simply because they have such large secondaries. The main optical problem for DSO imaging is astigmatism, since out-of-round stars will remain somewhat out-of-round even after convolution with the atmospheric psf - but astigmatism is generally caused by mirror mounting problems rather than the mirror, so you should be able to correct this type of fault. Minor diffraction can also influence saturated star shapes, since you see the skirts of the saturated PSF and any minor sprays of light from intrusions into the light column will distort the star shapes, even though unsaturated stars look OK.

My guess is that you will find that a GSO mirror is great for DSO imaging. Interested to hear what others think. Regards ray.