Zenza Bronica released four generations of film back for ETR System cameras. The first three of these had a non-locking dark slide, which could be removed from the back at any time—even when it was loaded with film. The final film back version, released with the ETRSi generation of camera bodies, included a dark slide lock, amongst other improvements.
This lock ensured that the dark slide could not be removed when the back was detached from the camera body, avoiding any accidental light exposure to loaded film.
However, sometimes it is necessary to remove the dark slide without the back attached to the body—particularly when testing or servicing a film back. Thankfully, it is a very simple process.
The photograph below shows the location of the locking tab, on the front of the film back (the side that attaches to the camera), in the bottom left corner (the side you remove the dark slide from).
To remove the dark slide, push down on the locking tab until it is almost flush with the film back frame. You can use your fingernail to do this, or a tool such as small flathead screwdriver. While the tab is depressed, pull the dark slide out.
Note that you will also need to depress the locking tab to reinsert the dark slide.
One last thing—the lock only works when an ETRSi generation dark slide (with a grey handle) is used in an ETRSi generation film back. If an ETRSi generation dark slide is inserted into an earlier generation film back, it will not lock. Neither will an earlier (black handled) dark slide lock when insert into an ETRSi generation back (although you will need to depress the locking tab to insert it when not attached to the camera body).
