Shooting the moon is often fraught with errors and while I appreciate the effort, you have three significant errors in this attempt. First, your focus is off enough so that all my post processing skills couldn't put it it right and your focus is off because likely you did not have a tripod sturdy enough to support that much lens which in turn shifted the focus a tad, but in the realm of 240,000 miles, a tad sends you into the sun and not on the moon's much cooler surface. Second, you underexposed by at least one and a half to two stops. Underexposing also affects dept of field, thus focus. Third, in post, you didn't remove the brown color cast. While the moon has many more colors than white, brown is not one of the more predominate colors.
So, at 1200mm you create your own set of issues. Optimally, with the Sigma 150-600 you would shoot fairly close to what I shot with my Nikon D500 (1/2 frame) and the Sigma 60-600 f/9, 1/250, ISO 320 -.33 EV mounted on an Artice Carbon Fiber Tripod/Benro head. I am not sure what you used for your exposure, but suspect a much lower shutter speed, a much higher ISO and a f/stop twice what it needed to be. Keep in mind, the moon moves and any exposure under 1/60 is going to create some blur, kind of like shooting a flower is a whisper breeze.
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