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I'm using Cycles and finding that the image I see in the 3D Viewport (when using rendered shading) is far crisper than the final render produced with Render Image (F12). I can't work out why.

First, the render as seen in the 3D Viewport (you can see the 3D Cursor) etc.:

3D viewport render

And now the dramatically blurrier Render Image result:

render image result

I'm guessing this bluriness is somehow supposed to be truer? I.e. the crispness seen in the 3D Viewport is a result of not being such a true renderer, i.e. various short cuts (in addition to fewer passes) are at play here. Other differences, I can see are e.g. that the final render includes a definite shadow (that for some reason is not visible in the 3D Viewport view).

I've looked at the Compositor and Shader nodes and I see no obvious reason for the bluriness.

This sphere has been added into an environment created by tracking. I.e. I shot the background footage, solved for the camera motion and then let Blender set up the tracking scene which resulted in a cube (which I replace with a reflective sphere), a shadow-catchter plane and the following Compositor nodes:

Compositor nodes

And then I added my own HDRI (which you see reflected in the sphere) with the following Shader nodes:

Shader nodes

The .hdr file, the .blend file and the background .mkv can be found here:

Any insight into what's going on here would be much appreciated.

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You have motion blur enabled. This, understandably, makes the render blurry. Because motion blur can dramatically increase render times, it is not calculated for a rendered preview.

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  • $\begingroup$ Super - I really appreciate people taking the time to answer questions that must seem painfully obvious to them but are completely non-obvious to people like me who are just trying things for the first time. I looked for issues with the nodes etc. and it never occurred to me that it might be a desirable effect, enabled to make things look better when movement is involved. $\endgroup$ Commented Nov 24, 2021 at 21:04
  • $\begingroup$ @GeorgeHawkins No problem-- I hope I didn't sound like I was talking down. I know that it's often nice just to get another set of eyes on a problem. In general, render/preview disagreement isn't going to be from mats, but from object visibility, render settings, subdivision settings, or particle settings. There may be an exception here and there; it's kind of a shame that there's no "make it like preview" button. $\endgroup$
    – Nathan
    Commented Nov 24, 2021 at 21:23

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