D7100 low light

Is f-8 was right or should have been more open?

Why did you choose f-8? I could see using a small aperture if I had subjects at different distances and I needed the added DoF but if you're shooting a flat object and everything about it is the same distance from your lens then most certainly use the largest aperture you have available and knock your ISO down to something more reasonable

On the other hand, it might not be only the DOF that matters here - I think the kit lens Nikon 18-55mm 3.5-5.6G exhibits lots of softness in the corners and a bit of vignetting too, if it is not "stopped down" to 5.6/8 at 18mm...

Well I didn't realize I had it on f-8 till after I took the shot. Have a bad habit of not looking at settings and just trying to make sure my focus is sharp.
But also didn't know about the flat surface and same distance thing.
Was trying to see the noise thing at higher ISO.