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Hi,

At first you need to set UCSFOLLOW system variable to 0 (zero) in Model space:

Command:
Command: UCSFOLLOW
Enter new value for UCSFOLLOW <1>: 0 <- type 0 and hit Return here

Then create layout and set in it paper size you need.
Now create viewport, activate it by double clicking inside viewport and roughly zoom to the area you want to see in the viewport.
Then use Status Bar to set scale of the viewport to 1:50, use pan to adjust view inside viewport. Activate paper space by double clicking outside viewport.

Look at layout with name "Layout with 1_50 viewport" in attached drawing.

Maxim