I’m also a member of “Ellingsen slekt” on Facebook. That’s why I have been looking on this blog.

Christensen is unknown, but Omenta worked in Trondheim between 1864 and 1884. If the names are stamped on with a rubber stamp, then the photo is from before 1873. If the names are printed on, then it’s from the last 11 years.

Here’s a web page that may be of interest:
http://www.nb.no/emigrasjon/emigration/ (The norwegian national library’s web page about the norwegian emigration to America)

Here’s a web page, also from the national library, where you can search between norwegian photographers, but unfortunately it’s only in norwegian: http://www.nb.no/nmff/