setaspect <viewingrange> <yxaspect>
is used to set the field of view in both dimensions in the original BUILD and Polymost renderers. (In newer builds, Polymer is affected too.)
<viewingrange> specifies the field of view as the tangent of the horizontal viewing angular radius, scaled by 16 bits (i.e. multiplied by 65536). The default value when playing with legacy aspect determination is 65536, corresponding to a FOV of 90 degrees. With r_usenewaspect, it depends on the aspect of the viewport.
<yxaspect> is the Y to X ratio scaled by 16 bits. In the editor, its default value is (65536*ydim*8)/(xdim*5). Note that <yxaspect> also affects rotatesprite.