What is it? Need help!

[J.G.C.]

I just picked this up in a grouping to a WWII 1st Div vet. It was in a box with some TR items, and I need some help to ID it. I thought it might have something to do with a hand gun, but I'm probably way off base. Its threaded on one end, and has an inner tube that will pull out and lock into position. The inner tube appears to be blued, and has the French word Renaux stamped into the steel. If anyone has a clue to what this is I would greatly appreciate some help. Jon

[J.G.C.]

Does anyone want to even venture a guess?

[me6_130]

Something to do with cameras or optics?

Carles