Dr. Nipun,
If you have not resolved your doubts yet, a legacy manual lens is a very attractive alternative. I use Canon FD lenses with the corresponding adaptor. They are quality optics, and while they aré inexpensive, there Is nothing "cheap" about them. Go for a 50mm F1:1,4, or a 85mm f1:1,8. they Willy give you equivalences to 75 and 127mm, which are ideal portrait focal lengths, plus the pleasure of manual handling.