Well, I'm happy to give my high-level, from-a-distance opinion. But optimal settings do vary from scene to scene. I've seen people create things that really did render better at Detail *2* instead of 1 (fortunately this is a rarity, and last I saw it was so many years ago it may no longer even be true with subsequent renderer improvements). So it's hard to make ideal recommendations without actually looking at the scene "live" and testing a few things. But I think giving good general ranges is at least helpful, so here goes (based largely on what you already mentioned as your settings, and recommendations for changes). Note that this is not a complete "set everything to this for all goodness all the time!" guide.
I think your .8/8 baseline is generally good for high quality, "final" rendering. Some vegetation may benefit from higher AA, but in general you're good at that level. It's the other settings that seem a bit unnecessary to me in some cases.
You already hinted that you understand 128 atmosphere samples is too high, and indeed it is. By a lot I'd guess. For the shot that is shown I'd be surprised if more than 32 would even show a noticeable difference, and the default of 16 is even likely to be sufficient (it's designed to provide good quality in normal daylight scenes, after all). Certainly there are cases where increasing atmosphere samples is necessary to reduce noise, but very, very seldom is 128 actually needed for any notable quality gain, and at that point it is generally giving diminishing returns. For complex *localized* light source situations, particularly with fog near the camera, higher atmo samples become more important, but this is a far cry from that. So I'd suggest backing down to 16 samples to start, then render some crops in the shadow areas of both terrain and clouds. That's where you're most likely to see atmo sample noise. In this scene, in the shadow side of the hills on the right, and the underside of the clouds. If you don't see noise, leave it at 16, if you do, raise to 32 and re-render your crops. I would be surprised if you need to go above 32.
Soft Shadow samples 32... OK, so the default is 9 here. IF you haven't changed the soft shadow diameter, then it's largely unnecessary to increase the samples. In most cases any small amount of noise due to undersampling at 9 samples is going to be hidden by rough terrain, vegetation, etc. However if you absolutely must have max quality, then you could increase to 12 or 16. 32 is absolutely unnecessary, in fact I"m not sure I've ever used a value that high. Soft shadow samples seem to be impactful numerically than others, evidenced by the default of 9 vs. 16 for atmosphere for example. So upping to 12 or even 16 has a big impact both on render quality (in difficult soft shadow situations, like larger shadow diameter), and on render time. Use 16 at most unless you're seeing significant noise in a clean and obvious shadow area, which is just not visible in this scene.
Clouds at quality 4... now you're just yanking my chain.
OK, so I can see why someone might do this sometimes... but your clouds do not appear to be that challenging and complex. It really should not be necessary. *Especially* with a detail of 0.8. Keep in mind that when Defer Atmosphere is off, the Detail setting interacts with the Cloud Quality setting to produce the final quality. A cloud quality of 1 with a Detail 0.8 should give pretty high quality final results. Quality 2 *might* be necessary with Detail 0.8 when you have more complex, high density, sharp-edged clouds. I would seldom, if ever, go to 4, and then only when main detail was lower, most likely. I also use Defer Atmo/Clouds sometimes, though it is more complex to tune correctly and I don't recommend you do so in a scene like this (too much vegetation that requires high AA for it to be really beneficial).
Finally, the 2 sun approach. Ok, I know this is advocated by some notable artists here, so I'm not going to argue against it on principle. I just continue to be unconvinced that judicious use of other options such as Enviro Light "Strength" sliders cannot produce the same or similar effect, but with more realism and "correct" results. Hopefully you're not using soft shadows on that 2nd sun, regardless.
Also, more generally, consider that rendering at higher resolution can often be more beneficial overall vs. super high settings, and this is more feasible the better your render times. So you could, for example, get faster render times by allowing a bit more noise in the render, but then render at higher resolution and get overall benefit. Just something to consider since your image here is a tad low resolution. Tying into this is the consideration of what is a test or experiment vs. "final" image (I know many of us seldom actually have "final" images, hehe). Where possible, it's best to keep the really top-quality settings for your "final" output, basically. Intuitive stuff, but I know the temptation to crank up settings can certainly be strong.
Regardless of all that it's a gorgeous-looking scene. Hopefully the above will help you iterate faster and crank out new versions, updates, improvements, and variations with ease. Let me know if you have any remaining questions.
- Oshyan
