I photograph small birds in the backyard from a deck and it is a focal length limited scenario. I like the vantage point I have from said deck and moving around or trying to get closer would scare the birds off. I have a 7D II + 100-400 II for birds in flight. I want to use my Sigma C 150-600 (tripod mounted) as a second body combo for static shots of birds. My thoughts are that the extra focal length will put more pixels on the subject.
I would love a 600mm prime but I don't want to risk a 1st gen Canon due to age/possible failure.
I've been thinking about which body to use with the Sigma. The birds are small and at varying distances. I've been thinking and reading so much that my brain is in a fog and I would like some input please.
My main thought is: is it better to use a full frame body for the IQ or a crop body for the pixel density?
I did a test scenario with my 6D @ 600mm & 7D II @ 400mm so the resulting photos were very similar. The 6D came out sharper for fine feather detail. But I may have goofed and had my shutter speed to low on my 7D II.
The options I have are: 6D, 5D II & Sony A6000 (1.5 crop) and I'm open to other options.
With the MP difference (20-24) being so small, maybe a prime telephoto is the better answer?