Doldurma bardağı. Sadace yarı bardak is Istiyorum. 

Don´t fill the glass. I only want half a cup.

Just an additional question, how could the above be said in a polite way.

Thank you

I think you can use Aorist tense for polite requests: http://www.turkishlanguage.co.uk/aoristpos.htm

But I´m not sure in this case what word that would be.

What did you mean with ´is´ in your second sentence?

Denizli thank you

Tunci what are your thoughts on this please? Thank you

If someone is pouring a drink [fruit juice,water or whatever] for you, in front of you, then it will be sufficient to say as follows :

Tam doldurmayın, yarım bardak yeter. 

Above, the suffix -ın will make the statement polite enough.

Tunci thank you