Pentax smc -FA Operating Manual page 13

How to Use the Square Hood
Attach the square hood to the front of the
lens while pressing the knurled tabs on both
sides of the hood.
Make sure to keep the top and bottom of
the hood parallel with the top and bottom
covers of the camera.
The improper fitting will cause the
vignetting in the picture corners.
How to Use the Round Hood
The round hood screws into the front of the
lens.
The round type rubber hood can be folded
when not in use.
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