i just have a quick question
i have access to some "mind switch" where following symtoms are generated in a few seconds after i hit it

1) the switch: i focus on the feeling of some form of vacuum inside my head when i concentrate on it gets stronger (head gets more empty)
2) kundalini-syndrome head pressure (which usually gets stronger when i concentrate) decreases
3) plus i get a strong sinking feeling
4) while i am sinking and sinking i feel more and more peacefull
5) turning my attention to my limbs (when i stop the sinking and come out of it) i recognize warm but harsh vibrations, opening my eyes the focus seems to be directed at some point maybe about 70cm away

could this be the entrance to the third jhana?
does somebody recognize this empty head feeling?

This could be in the neighborhood of first jhana. Eyes focused to a point is more characteristic of 1st/2nd jhana. 3rd tends to have a focus on the periphery but not on the center. Often described as a donut.

thanks for the answer
I can't tell where my eyefocus is, when my eyes are closed while doing this. It is only when i open them the first thing that goes from blurry to sharp is some object 70cm away. I will try to do this with open eyes to figure out what exactly happens.

are you already navigating 1st/2nd jhana with relative ease?

sounds like 3rd to me. The 'sinking feeling' and decreased 'head pressure' (which I equate to MCTB's use of rapture) are what I use. I actually focus on 'effortlessly sinking into the tingling' in arms/body to shift from 2nd to 3rd somewhat reliably.

i am navigation the first three vipassana jhanas with relative ease
for entering a stage which seems to me the beginning of the first samatha jhana i start with this sequence
1) focus on on kasina, e.g. a candle flame
2) i notice holding on to it
3) this holding on is being let go of automatically at some point, eye focus widens, concentration is "easier"
4) now if i excert some effort to bring the eye focus back to the middle of the flame piti arises from the lower part of my body
5) taking piti as a concentration object it is getting very strong

so this is would be the entrance to the first jhana for me

i guess the second samatha-jhana would reveal itself by concentrating on the piti-sukha of an a&p
i just had problems to figure out something nice in the dukkha nanas to focus on, so that is why i asked the original question