Unknown accessory.....

..found in bottom of monorail flight case - front & back views

any clues? looks like some kind of meter cell booster thing to me

old Canon?minolta perhaps?

My father has something similar to this in his photographic kit. I think it is an attachment for a light meter. I'm not sure of it's purpose, maybe it increases sensitivity for extremely low light readings?

Sekonic low light selenium cell 60's era

The sekonic meter - sorry, was my dad's circa early to mid 60's unit, so I do not recall the model number, had a film exposure dial with a red, yellow and blue dot.

With the meter door with a slot in it closed (bright situations) you set the dial to match the meter needle at the red dot. (Less bright) you flipped the on meter door open, and matched the needle to the yellow dot. (Usually indoors) you plugged the low light cell , shown in you picture, into two socke holes in the bottom of the meter, kept the on meter door open, and metered to line up with the blue dot.

There were transluent panels that were slipped on for incident readings.

Quite sure that what you have here is the low light cell. If it has been kept in the dark it moght still work; selenum cells get less sensitive with years of use. If yiu have the matching meter, it will probably work. Never needs batteries, or has them die when you are shooting in the winter.

Cool. That is what I supposed but since I do not have the meter and I don't know the history of the part (it came from an auction of bankrupt photo studio) I guess its just a paperweight.