Need a bit of help here .
I own both these lenses, and given that using a 1.4x loses about 1 stop (is that right?) , am I better using this with the 70-200 2.8 instead of the 100-400 for shooting birds about 12ft away when the light is fairly dull?
Small finch-sized birds.
I am finding with the 7D that the iso has to be quite high using the 100-400 if I want about 1000 shutter speed. Aperture about 5.6 to blur background.