Vivitar 7MM-C Instruction Manual page 8

Camera Settings
Some cameras require special settings when using this lens. Please read the information
below and set your camera accordingly.
The aperture of the 7mm fisheye lens is not specifically geared to your camera.
If the F stop is set above 8, you may not be able to set the correct focus due to difficulty in
viewing the subject through the camera's viewfinder. Turn the aperture adjustment ring and
fully open it when attaching this lens to the camera, and then turn the aperture adjustment
ring again to set the depth of focus and brightness you want prior to shooting.
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