Added 1683055617 by Timmee.
Single Nikon SB-800 speedlite (with push-fit diffuser cap) inserted in 100cm Deep Oct. In this case set on remote TTL and fired with another SB-800 on Bruv's D3X.
We wondered if a single speedlite would fill the relatively large Elinchrom 100cm Deep Octa soft box. It seems seems to work fine.