I recently came across this picture and I'm curious about the accessory on the left side. Does anyone have an idea what it’s used for?

Film photography subreddit. Ask anything about analog photography in our weekly "ask anything" thread, or share photos. For discussion of how to shoot film, buying advice, or what went wrong on your first roll head on over to /r/analogcommunity.
I recently came across this picture and I'm curious about the accessory on the left side. Does anyone have an idea what it’s used for?

Assembling Lens Cap Nikon AF600

A community dedicated to repairing analog film cameras, old lenses and vintage photography gear. A place to ask questions, share information and discuss techniques. To get Expert or Professional user flairs please message the mod team.
Weiße Stäbchen bei Datteln

Ihr sucht Expertinnen und Experten, die euch beim Erkennen von Dingen, Personen, Insekten, Orten auf Fotos oder beim Erinnern an diesen einen Film oder dieses eine Musikstück helfen? Dann seid ihr hier richtig!
Achieving this look by Jacques Olivar

A forum for professional photographers and cinematographers (DOP) to guess or share the lighting, lighting tools, modifiers, diffusion, photography EQ, grip, gaff, camera settings, lensing, lighting diagrams, lighting design, post processing, used in any particular photograph creating visual effects in studio and out.
Photography Vernissage Tonight!

Welcome to BerlinSocialClub, the subreddit for arranging meetups and hangouts in the Hauptstadt. Auf Deutsch kann selbstverständlich auch gepostet werden. Telegram links and link-shorteners will be censored by Reddit, be creative and insert spaces or similar. Please don't ask for drugs, or post or comment anything that breaks Reddit TOS. BSC also welcomes chatty posts and enquiries here, but they have to remain civil, non-political, and pertain to Berlin and its social scene. Viel Spaß!
Photobook Talk Berlin

r/photobooks is a place to discuss published or yet to be published photo books, share thoughts, sell and buy. A 'photo book' is any book in which one or more photographers have made a significant contribution. This is not a place to share your personal photobooks.
Berlin Photobook Talk
Welcome to BerlinSocialClub, the subreddit for arranging meetups and hangouts in the Hauptstadt. Auf Deutsch kann selbstverständlich auch gepostet werden. Telegram links and link-shorteners will be censored by Reddit, be creative and insert spaces or similar. Please don't ask for drugs, or post or comment anything that breaks Reddit TOS. BSC also welcomes chatty posts and enquiries here, but they have to remain civil, non-political, and pertain to Berlin and its social scene. Viel Spaß!Photo Book Talk Berlin

A place for the film photography/videography community to discuss whatever you want. The sister sub of r/analog, where all of the non-photo-sharing stuff happens!
Hasselblad 500cm T-Max 100 in Montenegro shot by Armin Mukladzija

Film photography subreddit. Ask anything about analog photography in our weekly "ask anything" thread, or share photos. For discussion of how to shoot film, buying advice, or what went wrong on your first roll head on over to /r/analogcommunity.