What is f- means in digital camera? - 1

I have Nikon n90, Many times when I want to take picture, the camera does not allow me to do anything and it show: f--
What should I do what is wrong?

"f--" happens when there's a communication problem between the camera and the lens. This is a common problem with the n90 and the 18-55 kit lens as well as the 18-105. The error is rectifiable by either twisting the lens (as contact misalignment is common with plastic mount lenses) or sometimes by powering cycling the camera.

The steps for prevention seem to be making sure the metal contacts (balls) on the lens are kept clean or using a higher quality lens with a metal mount.

Read the manual. If you have none, hunt one down at http://butkus.org.

Most probably, your lens is not set to smallest f/number and you are using the camera in A, S or P mode. If it's not that case, try cleaning the electrical contacts of the lens and the camera at the mounts. Use a dry cotton bud or a clean pencil eraser making sure nothing drops inside the lens or camera.