Canon RF-S3.9 mm F3.5 STM DUAL FISHEYE Instructions Manual page 17

Filters (Sold separately)
Only one filter with a thickness of 0.2 mm/0.008 in. or less may be used.
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When printing the template, make sure that the illustration size remains the same. Check that the printed-out
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size is the same as the measurements shown in the illustration.
Cut along the middle of the lines printed on the filter template. Any deviation from the template line width can
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cause the following issues.
Note 1: Cutting inside the line can lead to the filter not being held securely in the rear filter holder and
slipping out of place.
Note 2: Cutting outside the line can lead to the filter not fitting in the rear filter holder.
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