How to observe the edge of the R face neatly

When R is attached to the edge of a workpiece, it may not be seen clearly.

You can see clearly by devising magnification, lighting, background.

I tried to observe the edge of dry cell 乾電池を観察

1. Difference in depth of focus (compare at 80 times)

Open the aperture Close the aperture
絞りを開放 絞りを絞る
If you open the aperture, the depth of focus will become shallow and the edge may become blurred.
2.Difference in background color (compare at 80 times) 
When the background color is black When the background color is white
背景が黒 背景が白
The edge may be blurred due to reflection of the background, reflection of the edge part due to lighting, shadows.
3. Difference in magnification  
The depth of focus also varies depending on the magnification. (open the aperture and compare)
at 30 times at 80 times
30倍時 80倍時
Even with the same object, the edge may become unclear if the magnification increases.