By 
Aperture value “F”
Basically, when you want to blur the background and make your subject stand out, set it to the open value
There are 9 diaphragm values
| F1,2 |
| F1,4, F1,6, F1,8 |
| F2,0, F2,2, F2,5 |
| F2,8, F3,2, F3,5 |
| F4,0, F4,5, F5,0 |
| F5,6, F6,3, F7,1 |
| F8,0, F9,0, F10 |
| F11, F13, F14 |
| F16, F18, F20 |
| F22, F25, F29 |
The smaller the aperture value, the smaller the focus range becomes.
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