Is this an older manual focus lens? If so, it lacks the electronics to communicate with the camera. You have to set the camera to Manual exposure mode (turn the mode dial to "M"). Set the shutter speed on the camera body as usual and set the aperture by turning the aperture ring on the lens. You'll have to set the exposure without any help from the camera's light meter.
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Is this an older manual focus lens? If so, it lacks the electronics to communicate with the camera. You have to set the camera to Manual exposure mode (turn the mode dial to "M"). Set the shutter speed on the camera body as usual and set the aperture by turning the aperture ring on the lens. You'll have to set the exposure without any help from the camera's light meter.