The only camera I have with the "T" mode on the shutter dial is the Nikon F3. In this setting, you fire the shutter and it will stay open until you move the shutter dial off that position. Of course you have to cover the lens first before you move the dial off the position so that the movement will not cause any issues.
Unlike the T mode I described above, the typical bulb setting requires constant pressure on the shutter trigger to keep the shutter open. Usually a remote cable with the locking capability can be used to keep pressure on the shutter button to keep the shutter open for as long as you want. However, on Pentax film cameras with bulb setting and the shutter button lock - such as on the the MX, LX, KX, Spotmatic F and others, you can use this shutter lock to hold the shutter open for as long as you want after firing the shutter.
---------- Post added 12-17-15 at 12:01 AM ----------
Originally posted by Imp You can customize bulb mode on dslrs to be start when you press, stop when you press. Check your manual.
Of course this requires battery power . . .