How to decipher names

In doing research of my Great-Grandfather. Bernt Johansen, born 15 Jan 1880 at Vestre Toten, Oppland, Norway, some of the information I have found lists his name like this. Bernt Johansen Drogseth (Solberg). I would have known him as Bernt Saxberg. Any idea where Drogseth would come in? Thanks, Brian