Gordy,
Which camera are you using?
Normally I work to plate scale...if, say, you have a DSLR (5.7micron pixel) then the Plate scale at prime focus would be 1.22 arcsec/pixel
With the x1.5 you get around 0.81 arcsec/pixel, which is pretty good for average seeing conditions.
I use the CCDCalc to give a review of the possible results.
http://www.newastro.com/book_new/camera_app.html