Well look that you ar eusing a low settings for a realistic render:

In the antialiasing set object and shadow accuracy to 0,5 (this will let your image more sharpen)

In the Lighttning quality set acurracy to 1 (this will create a more precise radiosity without the spots)

This will encrease your render time but the final image will be great...you can save this settings for later use.

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