You might have a gummed up iris so the aperture won't set correctly.
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To find out with no film in the camera and the shutter setting to Blub alter the aperture from '''
+
To find out with no film in the camera and the shutter setting to '''Bulb''' alter the aperture from f 2.0 to f 16/22 if the blades slowly move you'll need to get your lens serviced.
You might have a gummed up iris so the aperture won't set correctly.
To find out with no film in the camera and the shutter setting to Blub alter the aperture from '''