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In a previous question, I asked about my exposure problems and there I found out that my lens cannot adjust the aperture/aperture blades. Every time I try to adjust the aperture to a higher number my and take a picture, an error comes up. I tried to check the lens and I saw that the aperture didn't change, thus giving me an error. Sometimes, the aperture blades also gets stuck and doesn't go back to its original position. I've tried cleaning the contacts of the lens and camera but the camera and the lens still loses contact. I also tried borrowing another lens, adjusted the aperture and the camera still loses contact with the lens. It seems my camera loses contact with the lenses every time I change the the aperture, though it works fine if I use the smallest available aperture. What is the possible cause of the lose of contact?
Camera: Nikon D90
Lens: AF-S DX NIKKOR 18-55mm f/3.5-5.6G VR II
Thanks in advance!