There has been quite a bit of buzz of a new Flash Gordon film coming in the near future and for most of us, many of us were introduced to “Flash Gordon” via the 1980 film starring Sam Jones (for others were the animated incarnations).
But before the ’80s film, there was the 1936 television series starring Buster Crabbe and Jean Rogers (and before that was the comic book strip by Alex Raymond).  The following photo is among the few “Flash Gordon” 8×11 prints that I have and in this photo is Flash (Crabbe), Dale (Rogers) and King Vultan (Jack “Tiny” Lipson).
Thanks to Rick Lanham for the following information:
It appears to be a still taken on the set of:
Flash Gordon: Space Soldiers
Chapter Seven: Shattering Doom
About 2 hours and 5 minutes into this DVD
I don’t see any place in the chapter where the spear is in Flash’s hands in exactly that way, but people are about in the same positions.
Your photo is a lot darker than the DVD, making Dale’s robe look black, when it is really gray.
Reference:
Flash Gordon 3 DVD Set
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ID9789HEDVD