A picture is worth a thousand words, so
Yep, your images show the difference between a typical mushy C1 preview at fit size (a couple of magnification steps in, this problem disappears) and a correctly rendered output.
Am I assuming correctly that your output is not the result of using a recipe that includes output sharpening? If extra output sharpening is applied then this obviously explains the crisper rendering. From my experience, however, even with no additional output sharpening added, exported files look better than the standard C1 Viewer previews.
I encourage you to create a
support case with Phase One. You should attach your evidence and/or point to this thread. I had created a support case a while ago and I think after a while my issues were appreciated, however, I have the feeling that the programmers are still struggling to find the right compromise between rendering quality and rendering speed.
Perhaps it is also a matter of only certain cameras / image sizes being affected?
I see others post about this issue here and there but there does not seem to be a real revolt of the masses going on.
Anyhow, the more people create a respective support case, the more Phase One will know that this is an issue that bothers more than a couple of users.
AFAIC, there is an easy (albeit potentially more storage-intensive) solution which just creates previews with the best possible quality at the fit size and caches them. Then these could be quickly displayed without requiring expensive re-renderings. I'd be fine with any delay when I start to zoom in (even if it is just a modest zoom step in). However, flicking through images at the fit size should be quick but without implying a rather mushy rendering.
If there is a price (in the form of rendering delay) to pay, it should be when I want to look really close. Currently, workarounds force me to pay a price when I'm just browsing or doing overall adjustments (that do not require 100% views and cannot be done at 100% views either).
Can anyone help with this?
Try setting the preview image size to the lowest size possible value (640). This may seem counterintuitive but it will force C1 to regenerate a quality rendering instead of showing you the mushy standard preview (which is probably downscaled from the higher-res, but not original preview data). I'm currently away from my C1 installation so I cannot double-check this approach but I'm pretty sure it helped me in the past (with V9). The downside to this approach is that you'll see the really low-res (640px wide) previews before they get replaced and that there is always a delay caused by the need to go back to the RAW (or already demosaiced?) data and compute the view on the fly.
N.B., you may have to force regeneration of previews and/or restart C1 to see a change to the preview image size have an effect. It is otherwise possible that you'll be served still existing renderings for a while.
The other solution is to simply pick a suitable proof profile and use the "Recipe Proofing" option (-> glasses symbol in the tool bar). The downsides of this approach are the distracting "Proofing" label in the Viewer area and, again, the delay caused by on-the-fly rendering of the proof view.