My renderings look blurred

[adryan_g78]

Hi, I'm a new Sweet Home user, although I've been using before modelling and rendering softwares.
This is a rendered scene that, I believe, looks ok, not professionally speaking, but as amateur.

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Now, I can't figure out why, using the same default settings of the software, my following scenes look blurry an noised.

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I tried to change the light efficiency, changed the ceiling light on and off, also tried to add light sources, but nothing good came out.

The advanced settings for renderings are chinese to me, I don't know what gaussian or mitchell filter means, nor samplerAlgorithm. I just left them to default.

Any ideas?
Thanks in advance! [:)]

[Puybaret]

Be sure not to choose the Depth of field lens which forces the focus distance to 250 cm with a limited depth of field.
Otherwise, the easiest way to get less blurred images is to enlarge their size (but this may take more time to compute).