Well the first test shows that 2.5 minutes are fine for the exposure.Thank you very much but now i have another Question:
Transparencies are plastic and plastic alters in UV exposure. Should i change the transparencies after exposing them for 3-4 times? or there is no problem and i can make as many pcbs as i want with the the first Transparencies i make(i type in plural cause i use 2 transparencies to make black color more solid)?