Visible crew/equipment: In the saloon scene where Doc passes out, a production light with barn doors and stand can be seen in the upper left over Marty's shoulder.
Visible crew/equipment: When Marty is with Jennifer in his new truck, as the camera cranes down to where they're talking, you can see a crewmember with a white shirt and some of the camera and crane. (01:46:10)

Visible crew/equipment: In the scene where Marty is chased out of the saloon in 1885 by Buford "Mad Dog" Tannen & his gang, in the shot showing Marty pushing his way between two women, the cameraman can be seen running along with the camera beside him to the left of the screen.
Visible crew/equipment: While McFly is running away from Mad Dog, beside him you can see a crew member and the camera.
Visible crew/equipment: When Doc's about to send Marty back to 1885 from 1955 at the open air cinema, you can see the shadow of the camera sticking out from the shadow of the building - it moves as the camera tracks Doc over to the car.
Chosen answer: According to the letter, Doc plans to live out his life in 1885. But as it turns out, Doc gets murdered a week after sending the letter. Knowing that Doc's plan to live out his life don't come to fruition, and because he's a good friend, Marty travels to 1885 to save him.
JC Fernandez