We have three pages and no one has mentioned coatings. Roland seems to think them important enough to use what he considers the best. The ones he specifies are expensive and are claimed to have a very high transmissibility.
Roland does not think of his big refractors as telescopes. He thinks of them as astrographs, and based on comments to me once, I think he might believe that using one of his scopes visually is a waste. For planetary performance, he pointed me to a 10" f/6 reflector as being a better choice than a 155 EDF.
The purpose of the coatings is I believe to allow greater transmission into the near infra red and ultraviolet. This is what rings his bell. A quote:
"The acid test was, of course, imaging and for that I added the dedicated field flattener and my STL1100 CCD camera. The results were everything I had hoped for. All the colors came to the same exact focus - no focus tweek required for any of them. Stars showed similar size and full width half max resolution with all 8 filter positions (RGB, L, H-alpha, OII and SII)..."
For visual use, you really don't need to go very wide. This is why the red Airy Disk is often allowed to be twice the diameter of the green Airy Disk in many designs. When it is kept to this size, the human eye simply can't see it. But the camera misses nothing. And for many photos, having high transmission at these more exotic wavelengths increases the ability to image large H-alpha features.
For visual use, coatings simply don't need to be so wide. For an astrograph though, it starts to become more important.
The AP180 f/9 says "hi".