How can I set the shutter to bulb setting on a Canon Powershot SX70?
2 Answers
It does not appear from the manual that the Canon Powershot SX70 HS has bulb-mode capability.
You can't.
Many small sensored cameras, such as the PowerShot SX70, limit maximum exposure times to prevent poor sensor performance due to heat buildup in the sensor. Even cameras with marginally larger sensors will often limit exposures taken with higher ISO settings to shorter times than exposures taken with lower ISO settings.
See, for example, these questions here at Photography SE and their answers:
Is there is an intervalometer compatible for Fujifilm FinePix HS20EXR?
Can I get longer than 15 second exposure with my canon SX 50?