I have been using a Nikon D5200 with a Tamron 100-400 zoom for wildlife photography. It's admittedly a budget setup (in some sense of the term "budget"), so I don't expect amazing results. I'm also not a trained photographer, and I've pretty much learned by reading the internet and youtube (not ideal, I know). Recently, I decided to rent a different Nikon body for an expedition (which ultimately got canceled due to COVID-19).
I decided to rent a mirrorless Nikon Z6 to see how I would like a mirrorless camera, and to try a full-frame sensor, and also just to get a newer sensor and body and see how the quality compares, using the same Tamron lens.
I made a lot of mistakes in using the new body, but ultimately I'm stumped still. The photos are displaying the same annoying glow that I've seen with the old body. I don't know what is causing it, but it seems like I can narrow it down to "operator" or lens errors.
In the image above, a heavily cropped section of a photo of a bird, you can see the glow. It shows up similarly using either body. This is shot at 400mm, ISO 320 f/6.3, 1/500 sec.
I handhold the camera most of the time because I just can't use a tripod for most of these photos (the birds are up in a tree, jumping around, etc.)
Does anyone have any suggestions for what I should do here? Should I use faster shutter speed and higher ISO? I've tried that and found that I get a lot of noise, but maybe the newer sensors can handle it? I'd be willing to spend some $$ on a book or read any references people might recommend.
EDIT This image is uncorrected, straight out of the camera, though (sadly) I took it as a JPG originally. I usually shoot raw, but had my settings incorrect for this new body that I'm renting. I see the same effect whether it's RAW or JPG though, it was just that this photo showed the effect more strongly so that I could illustrate my question.