Sorry, I was rushing out to get my Covid vaccine shot. I should have sent a finished image, instead of the raw image reduced to a jpeg. I thought we were discussing whether the eye focusing worked, for which that image was sufficient. if I knew it was a your were intent on criticizing my skills as a photographer, I certainly would have waited and finished up the image...probably should have done that anyway.

I have attached the image after some noise reduction, minor selective sharpening, minor exposure adjustments and removal of the gross sharpening that Lightroom adds. (I will need to do a preset in the future) The highlights are not blown, although the frontal lighting does not pick up much detail in the back of the head.

That the ISO and exposure decisions in your shot and mine are equivalent is just not so. You are shooting a single colored, stationary bird that is smaller and has far less depth. My bird is black and white with black portions in the shadows and white portions in the sun. It has a huge wingspan. I am shooting handheld with a focal length of 560mm. In order to keep the wingtips in focus, I chose f/11 at 1/1600 of a second at ISO That exposure allowed me to hold the highlights and not block up the shadows. If you look at the histogram, the is little play on either end.

You may like the shot or not, I don't particularly care. The question we started out discussing and for which the image was meant to show was whether the eye focusing works in the Canon R5 and whether it is advantageous when shooting birds in flight. I will leave it at that. I refuse to get into protracted and silly arguments

My cataract surgery on one eye was yesterday, recovering today. The cost of the upgraded lenses, in my eyes, has put a hold on my new camera body purchase. ( Please excuse any strange keyboard or spelling messups. Working with altered vision today.)
This led me back into the rabbit hole of why I want a new body (cause I'm not 18 anymore?).

I shoot mostly wildlife and of that mostly birds.very often from a moving platform, a boat.

From what I have been reading high pixel cameras are more sensitive to camera movement. This got me wondering about the 90d I have been lusting after. At 32 megapixels its equal to a full frame at 51 megapixels. I'm also trying to avoid more high iso noise. For wildlife, for me, speed is king.

This got me looking over the older 1D offerings with H size sensors.

I crop often, ok almost always, and sometime big crops.
So I'm wondering about pixel density and print image size. But the normal thoughts of 300 dpi for high quality printing a 16.1. Mp image (canon 1D 1V H. Sensor) would print a max image of 4896 x 3264 or 16.3"x10.8" but. We also know that for larger printing 300 dpi may not be necessary. Cropped at 50% would be 8x5. Of for web but not so good to print?

So I guess the question is, at what point does "blowing up" an image does an image begin to soften due to pixelation?

Along the same line.
I had a thought the other day when PS wanted to Rastorize (sp?) an image because of something I tried to do. (Still learning)
When an image is rastorized isn't that like the digital equivelant of a "line type" image? Would restorizing help to preserve detail if an image is being enlarged?

Thanks
Bill