….is affected by aperture – the lower the “F-number”, the more shallow the depth of field.
But let me repeat… also by lens length (the longer the lens, the more shallow the depth of field), and, importantly, by proximity. It is the relative distance difference that matters!
Same settings in these two pictures:
Slightly blurry background… Now with the same settings, but we get closer:
Tip: to learn these things well, use a prime lens. That takes one variable out of the equation.