My guess is the camera tries to go to a high ISO. Easy to check in NXview. Switch of the OS, put the camera on a tripod and use a low iso, to see if you can make pictures without grain (digital noise) I know that is not an option for you in the field, but just to see the lens and your camera can make beautiful pictures. Newer camera's can work with higher ISO, without seeing digital noise. Buy a second hand (new in the Xmas sales) D7000. You can easy shoot till ISO 3200 and hardly see any noise.
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My guess is the camera tries to go to a high ISO. Easy to check in NXview. Switch of the OS, put the camera on a tripod and use a low iso, to see if you can make pictures without grain (digital noise)
I know that is not an option for you in the field, but just to see the lens and your camera can make beautiful pictures.
Newer camera's can work with higher ISO, without seeing digital noise. Buy a second hand (new in the Xmas sales) D7000. You can easy shoot till ISO 3200 and hardly see any noise.