How does the bulb setting work?

[PlasticSpanner]

Does anyone know exactly the process how the Bulb setting works on a film SLR camera?

I have a Praktica BMS & the shutter seems to lock open and the mirror stays up even when the release is released! The battery should be OK as it was replaced 2 weeks ago.

Am I missing something simple?

 

[ksmattfish]

With some SLRs the mirror doesn't return to the down position until the shutter is cocked/film advanced to the next frame. But the shutter itself should definately close when released on the bulb setting.

 

[PlasticSpanner]

How does it do it?

Is it electrical or mechanical? I presume the mirror is flipped up & the shutter opened mechanically & closed by a spring return when the button is released?

Or is it controlled electronicly by a chip or processor?

This has totally baffled me as the camera works perfectly otherwise!

 

[Unimaxium]

It depends on the camera you're using. Electronic cameras with electronic shutters will use battery power to open and close the shutter when you press the button. But there are also purely mechanical cameras that control the shutter without any electricity.

EDIT: after a quick google search about the Praktica BMS it seems like your camera has an electronic shutter, meaning that it requires battery power to open and close it.

 

[PlasticSpanner]

Does it still need the battery to close it? The 4 sec shutter works fine & when opened & stuck on Bulb I can close the shutter & drop the mirror by opening the battery compartment & dislodging the battery. It seems like the electrics aren't being cut off when the button is released to finish the exposure!? Or is the something else in the process that I'm not doing or missing that is preventing the camera from completing the operation?