DOF and the use of extenders

[Edward]

If i shoot my 400 mm f 2.8 at f 4, adding a 1.4X makes it an f 4.  Is the depth of field the same with and without the extender at f 4?

[Skirball]

The discussion was entirely on effective aperture and DoF, there wasn't any confusion on focal length.  As you say, a lens with an extender will give you the same field of view as the effective focal length, in other words, to an external observer it will act exactly as a 560mm lens (IQ issues aside)...  so why muddy the waters further with an issue of semantics that has absolutely no impact to the discussion?

[ebiggs1]

Get up on the wrong side of the bed again?

Actually you can answer a query the way you like to and I will answer the way I like to, If that pains you so much, please, don't read mine. They don't concern you.