Was playing with the P645 600mm lens today and revisited the combo with the 1.4 teleconverter. I haven't used this lens for a while and when I opened the box I realized that I had since bought a clear filter for it. I recall reading somewhere that the lens is designed to have at least a clear filter in place. No idea if this has any real impact on the lens' ability to resolve better detail or not, but for good luck and prosperity the filter went in.
I found that the 1.4TC performed fairly well with the 600mm lens but not when the target is too far away. No idea why this is a factor. See the pictures below:
About a 140% crop of a mountain top with some rocks and foliage to see the ability of the lens and camera to resolve the details. The target is about 3km away. Some atmospheric disturbance, but I selected the best of a series of shots to avoid the worst effects.
The same mountain but with the 1.4TC and +/- 140% crop. Comparing the two pictures it looks as if the edges are reasonable but it starts to fail with resolving the foliage.
However at a nearby distance of about 25m the 1.4TC works fairly well with the 600mm lens. I think it does a fairly good job on the feathers, which are normally very difficult.
About 90% crop of the bird (I think it is a Bull Bull)
Comments and pixel peeping appreciated....