Blurring/Darkening

[mikelong]

Recently while photographing the night sky my shots came back extremely blurred on the right side with darkening on all corners. I contacted Nikon support and here was their response:

"Hi Mike, Thank you for submitting your photos. Upon evaluation we have notice that the focus was set to Manual mode. You need to manually adjust the focus on the lens by rotating the focus ring. It's hard to manually determine a focus at night because you cant really see how sharp is the image when looking thru the viewfinder. I would advise you to set the Focus mode to automatic. Regards."

Thanks Nikon, for the manual focus lesson (even though they're telling me not to use it...). They're suggesting I auto focus on tiny points of light with a wide-angle lens in the dark - not possible. How does using manual focus render stars sharp in the center and left side of the image, but totally blurred on the right when all stars are at infinity? They're suggesting auto focus will remedy this problem. And nothing at all about darkening of corners. In any case, perhaps someone here has a better explanation - I suspect a lens element is out of alignment. If not, truly poor results from a $1600 lens.

Click on the image for original version. No polarizer or lens hood was used, which could normally explain the dark corners.

Thanks
Mike

[hjew]

Some lenses will exhibit vignetting when shot at their widest aperture. You can try stopping it down and using a longer exposure time.

[mikelong]

The vignetting appears to be normal as you suggest. I virtually never shoot at the widest aperture but in this case had to limit my exposure time to 35 seconds (600 / 17mm) before stars began appearing as streaks or trails. Or bump my ISO up to 4000 and and stop down to f/6.7, but then digital noise becomes more of an issue. In any case, the right side blurring is not at all normal for this lens. Here's a second (better) response I received from Nikon this morning:

"Thanks for the update and I am sorry for the poor response you received before. Obviously you are correct that manual focus is not an issue here.

It is completely normal for there to be some softening (or other distortion) as you move from the center towards the edges of the frame but it should be generally pretty even from left to right and top to bottom. Based on your sample I'd suggest the camera and lens come in to be checked because I'd suspect some misalignment of the lens or camera mount.

Regarding the vignetting, this is completely normal. Light that travels towards the edges of the frame has to go farther than light that travels to the center of the frame. Light that travels farther decreases slightly. When you do a big exposure or tone adjustment this will be more obvious."
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I'm now convinced it's the body and not the lens after running some tests.