ALPA offers a complete range of 16 types of additively manufactured lens hoodsfor all HR Alpagon and HR Alpar lenses. The subtype "0" identifies the round lens hoods when using the full image circle. Subtype "1" is optimized for sensor sizes up to 40x54 mm without or only a tiny amount of movement (especially with sensors of smaller sizes than 40x54).
Therefore: The round subtype "0" versions allow movement over the lens's entire image circle without vignetting. The rectangular subtype "1" versions offer optimum effect without movement and for sensors up to 40x54 mm. They thus block the collection of stray light in the non-visible area that extends beyond the image circle of the recording format.