Release W/O Card; Silent Shooting (Still Image) - Sony ILCE-6500 Manual

an astronomical telescope, etc.
Disable:
Does not release the shutter when a lens is not attached.
Note
Correct metering cannot be achieved when you use lenses that do not provide a lens contact, such
as the lens of an astronomical telescope. In such cases, adjust the exposure manually by checking it
on the recorded image.
[120] Shooting Shutter settings

Release w/o Card

Sets whether the shutter can be released when no memory card has been inserted.
MENU →
1
Menu item details
Enable:
Releases the shutter even if no memory card has been inserted.
Disable:
Does not release the shutter when no memory card has been inserted.
Note
When no memory card has been inserted, the images shot will not be saved.
The default setting is [Enable]. It is recommended that you select [Disable] prior to actual shooting.
[121] Shooting Shutter settings

Silent Shooting (still image)

You can shoot images without the shutter sound.
MENU →
1
(Camera Settings2) → [Release w/o Card] → desired setting.
(Camera Settings2) → [ Silent Shooting] → desired setting.