[Brightcolours]

Does exist test for to know with is the best aperture for Sigma 105 at minimun distance of focus (about 32 cm ) and at another distance?

 

Many thanks.

There is no such thing is "best aperture, really, as JoJu points out.

 

For shallow DOF, wide open usually is best. For best contrast, closing down usually is a good idea. For most DOF, you need to stop down a lot, and for best sharpness, f5.6 usually is the best idea (for medium close up to infinity).

 

When you go close, the effective f-stop diminishes. 

See for instance this thread:

http://www.cambridgeincolour.com/forums/thread1358.htm

Your Nikon D800 will actually show a close approximation of the effective aperture (try it yourself.. set for instance f4 at medium distance, then focus on something very close up and you will see that the camera shows a different f-value than you originally set).

 

What is the best aperture to use totally depends on what you are trying to achieve for a certain shot.