Hi Julia @juliadu ,
My guess would be, that there is nothing to see through the ‘glass’. The inside of the binoculars is mainly dark (hardly any light reeaches there). In the screen-right glass, you can see some light through the back glass. If you are using an HDRI for the Lighting, and make sure the Roughness of the glass Material is quite low, you should see some reflections in them.
