I am experimenting a little with higher F-stops than usual and with the 2X converter....I like the extra DOF and I don't appreciate any loss of detail due to diffraction.

The technique only works if the bird sits very still for a few seconds, otherwise the slow shutter speed won't be adequate.

This is an American Goldfinch morphing from winter to summer plumage

1DX
1000mm
ISO 3200
f/13
1/200
No flash