Timed exposure question with D70S

Hi Guys,
Quick question I'm posting on behalf of a mate.
If he wants to get a long exposure on his D70S say around 30 minutes plus what does he have to do to keep the shutter open? Is there a setting he can use or does he have to hold his finger on the trigger the whole time?
Any help would be greatly appreciated and make me seem far smarter than I actually am.
Cheers
Ben
Quick question I'm posting on behalf of a mate.
If he wants to get a long exposure on his D70S say around 30 minutes plus what does he have to do to keep the shutter open? Is there a setting he can use or does he have to hold his finger on the trigger the whole time?
Any help would be greatly appreciated and make me seem far smarter than I actually am.
Cheers
Ben