I am new to photography. I have a Nikon D750 with the 18-200 f/3.5-5.6 ED VRII lens on it. No filters are attached. No hood is attached. When I look through the viewfinder, it creates a circle around the outside. This appears with the camera powered on or off. The circles are bigger (worse) at 18 than they are at 200. This issue started a month ago. I tried changing the lens and the circle disappears so I know it is with this lens only. Any suggestions how to fix this problem?
2 Answers
The D750 is a full frame camera, while the 18-200 lens is made for DX cameras, which have a smaller sensor. So the lens can't project a big enough image onto the sensor to cover the entire sensor, which is why you see the dark circles.
The reason your other lenses don't exhibit the problem is that they are likely all FX (full frame) lenses.
The reason it used to look normal is you would have had the camera in "auto crop mode".
In the Shooting Menu, under Image area > Choose image area select "Auto DX crop".
What this mode does is recognize that you have a DX lens attached and automatically crops out the dark parts at the edges.
I'm guessing that at some point you changed this menu setting.
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2\$\begingroup\$ Wouldn't the vignetting still be visible in the viewfinder even if the camera is in crop mode? \$\endgroup\$ Jan 22, 2017 at 18:03
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5\$\begingroup\$ I've shot with a DX lens on full-frame before (although with the D810). The viewfinder will highlight a rectangle around where the true image will be taken, but does not 'adjust' to not show the tunnel. \$\endgroup\$– WaddlesJan 22, 2017 at 22:43
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7\$\begingroup\$ I actually prefer to shoot in FX mode and crop later on. Because of this circle, you can shoot landscape and crop to portrait, which is actually pretty useful. \$\endgroup\$– WaddlesJan 22, 2017 at 22:46
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1\$\begingroup\$ @MikeW: What advantage would there be to shooting a cropped portion rather than capturing the whole thing and cropping in post? If the portion of the image one is interested in isn't a standard-aspect rectangle, pre-cropping would prevent one from using areas of the sensor that would otherwise have been just fine. \$\endgroup\$– supercatJan 23, 2017 at 17:35
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2\$\begingroup\$ @supercat Apart from saving space on your memory cards, I imagine this feature is aimed at all those people who don't want to spend time on post-processing. \$\endgroup\$– MikeW ♦Jan 23, 2017 at 18:06
Don't use 18-200 3.5-5.6 ED VRII on D750. That's DX (small) lens on FX(big) camera, the result is heavy vignetting, as you describe. Or the camera switching into FX crop mode. It's pretty much "a waste of full-frame camera", as you'd get better results when using much cheaper DX body.
Get a 28-300mm f/3.5-5.6 VR instead. This is the closest FX equivalent of 18-200 on DX. As a proper FX lens, it will let you use full potential of your FX camera.
If this setup was sold to you recently, I believe you should be able to return the 18-200 lens. It's not a appropriate match for D750. If the seller told you so, he mislead you.