Tele lens for shallower depth?

[godzilla60]

Hi guys,....

i was wondering if i wanna get a shallower depth, i need to get as big a lens (i mean 500mm as compared to 100mm) or is the aperture playing the part?

e.g which will give a shallower depth?

50mm @ f1.7
100mm @ f2.8
200mm @ f2.8
500mm @ f3.6

thanks for tolerating another noob qn from me...

 

[J-Chan]

Depth of Field Calculator

 

[godzilla60]

does DOF affects the softness of those out-of-focus areas?