Hey Rebreb,
If a scope is able to be passed through the ileocaecal valve they can usually reach perhaps 15cm (6") into the distal ileum.
From the top end they can reach through the stomach and into the duodenum. Depending on the length of the scope they may be able to reach through the duodenum into the start (proximal end) of the jejunum.
Considering the small bowel (Duodenum, Jejunum, Ileum) is approximately 7 metres long very little is able to be visualised by scopes.
Dusty. xxx