What causes this artefact

[bhop]

It seems you've already gotten this taken care of, but I was going to ask if you changed lenses in bright sunlight.

 

[omtech]

Looks like a light leak of some kind.

 

[Christie Photo]

I know the post goes back to June. Just wondering... who did your film processing? I've seen similar results when film is damaged while loading it on the spool. What I saw was more of a crescent shape and it typically occurred on 120/220 film.

-Pete