Canon RF-S3.9 mm F3.5 STM DUAL FISHEYE Instructions Manual page 21

Specifications
The lens length is measured from the lens mount surface to the front end of the lens.
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Add 24.2 mm/0.95 in. when including the lens cap and dust cap.
The width, height, length and weight are for the lens itself only.
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Close-up Lens 250D/500D cannot be attached because there is no size that fits the lens.
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You cannot use extenders.
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All data listed is measured according to Canon standards.
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Product specifications and appearance are subject to change without notice.
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ENG-20