In fact, in September the Northern Lights were visible in my area. One of my friends who has that D750 just left her camera home and used my D3s. Her camera never would have gotten the shots. Even using a tripod or monopod. My friends with that camera have tried the tripods and monopods and they just can't get the shots I can get because of their cameras.
Why? What specific capability does the D3s have, or what feature does the D750 lack that only would allow the D3s to capture the Northern Lights?
I have no idea what why they have problems with their cameras and I don't.
You would have to ask them.
I do know that my friend didn't even bother with her camera that night. She said it would have been a waste of her time to try it with her camera.
I do know that it won't take clear photos at low aperture speeds and f stops like mine will. I can shoot hand held in low speeds and the photos come out just fine. Their photos end up with a lot of noise in those situations and others. Their ISO doesn't go as high or low as mine.
Here are some shots of holiday lights. The shots were taken in 2018. They were taken on a D3s camera with a 75 to 300 lens. My friends with their 750 cameras were with me. They had tripods. I shot hand held. Even with the tripods they had a hard time with their cameras while I took seconds to take the shot and move on.
I shot this with a star filter on the lens. It was at Iso 12800. The aperture was at 1/30 and the f stop was at 4.5.
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I shot this one at ISO 10000. The aperture was at 1/50. The F stop was 5.3.
Most of the photos my friends took that night came out with a lot of noise and not clear.
The next time I shoot with one of them I will ask them more about their cameras.
I don't know much about the non professional cameras. I haven't used one in decades.