about DOF

Will there be any difference in DOF of 400mm,5.6 at f/5.6 and after addition of 1.4 t.c. resulting f/8?

Yes.

Depth of field is dependent on focal length, aperture as well as distance of the subject.

When you attach a 1.4x TC to the 400mm f5.6 lens, the resulting combination is 560 mm f8. The depth of field will become much narrower.

thanks Sabyasachi, but after attachment of t.c., will there be any physical change in diaphragm ?

Hi Jitendra,

There is no change in diaphragm when you add a TC. F stop is the ratio of focal length and size of the lens opening.

for example, lets consider 400 f5.6 lens

When wide open i.e. at f5.6, the lens opening is around 71.5mm

F stop = 400/71.5 = 5.6 (approx.)

when we add the TC the focal length increases. 560mm for 1.4x. The diaphragm and the lens opening remains the same.

F stop = 560/71.5 = 8 (approx.)

This is how we get 560mm f8 with 1.4x. Similar is the case with 2x TC.

Hope this clarifies your doubt.