The well known Canon 15mm fisheye lens - by Sigma?

I just received the news that the classic full frame 15mm fisheye by Canon has been discontinued and will soon be unavailable when the stock has been sold out. This is very sad because this lens is extremely useful and difficult to replace by something else. Some customers may select the new EF 8-15mm f/4L which has been introduced but in my opinion this is not a full replacement since the original fixed focus fisheye is faster and possibly sharper.

Canon 15mm Fisheye lens with Sigma lens cap

Sigma has a 15mm f/2.8 prime lens that is extremely interesting and can be used as a replacement. I have not tested the Sigma lens but I think the Sigma lens is the same design as the Canon lens because I think Sigma is the manufacturer for the original Canon 15mm lens since my copy of the Canon 15mm lens was delivered with a Sigma lens cap! I do not know if this is true for all copies of this lens but please check the backside of the rear cap for the Sigma logo next to the text “MADE IN JAPAN”

Canon 15mm fisheye lens cap by Sigma

The rear cap look exactly as the lens cap delivered with Sigma lenses with the text “FOR CANON AF” printed on the front. I compared this cap with a Sigma cap delivered with a 8mm fisheye and they are identical, I suspect they where manufactured in the same machine or at lease with the same tool because the typical injection mold markings where the same on both caps.