What is the longest Bulb exposure with the a7/a7r?

[mjm6]

I'm doing some research at lunch, and have not been able to find this information on the web or in the manual...

Is there a time limitation to the Bulb exposure? Is it limited to battery life?

What happens when a long exposure is done without the NR turned on, does it get very grainy?

Does the NR setting do a second dark frame exposure?

I'm thinking about star trails, etc. and want to understand the limitations of the camera.

Thanks,

---Michael

 

[mjm6]

I didn't get a chance to test some of this out last night, so if anyone has done so, please let me know...