Upvote:2
I may have missed an earlier (later modified or deleted) message, but I am a bit confused. Why is people talking about two entries? Do you already have a dual-entry Schengen visa or are you asking about what visa to apply for?
Travelling like this: non-Schengen -> Belgium -> Finland -> Belgium -> non-Schengen would use up one entry on a Schengen visa.
Landing in Belgium you will go through passport control there. It does not matter whether you chose to leave the airport or continue straight to your connecting flight. In Belgium your passport will get an entry stamp and the clock will start or your time in the Schengen Area.
Arriving in Finland your passport will not be stamped as you arrive from within the Schengen Area (having been checked in Belgium). Returning to Belgium will not get you any new passport stamp either and you will still be on your first entry. It does not matter how many times you travel back and forth.
Eventually leaving the Schengen Area from Belgium you will get you an exit stamp and the clock will stop on your time in the Schengen Area.
If this is your complete itinerary in the Schengen Area you need a single-entry visa. Your stay in the Schengen Area will be 10 calendar days, so a 10-day visa will be enough, assuming your departing flight is not delayed. Unlike some other countries, it is not enough for the visa to be valid on arrival; a Schengen visa must remain valid until you eventually leave the Schengen Area.
Upvote:15
You can enter the Schengen zone twice. A direct flight between two Schengen countries or through a third Schengen country does not mean leaving Schengen. A flight through London or a similar non-Schengen airport would mean leaving Schengen.
So everything is fine if you go directly from Belgium to Finland.