Canon 6d2_ Canon 70-2002.8 lens plus 2 times rangefinder can take clear photos of birds?

Rangefinder is the product of compromise among image quality, price and volume, and the final image quality is directly related to the quality of the original lens.

The higher the resolution of the original lens, the worse the image quality after adding the range extender, and the decline is certain.

So, to sum up, if you shoot birds with a 70-200/2.8 lens plus a 2-fold zoom lens, it is ok, but the scope of use and the picture quality can only be described as guest appearances (non-feverish bird friends), and it is impossible to change the bird head of the relevant focal segment.