mranch1 Does anyone know if it's possible to set the f stop somehow?
Do not use a camera lens at maximum aperture. You will not be happy with the results.
If you don't want to use the iris in the camera to set the aperture (which can produce 8 or 12 diffraction spikes), use a set of what are called "step-down" rings; your local camera store has them, and so does Amazon. Try for at least 1 f-stop below the wide-open f-stop of the lens, while setting the lens itself to be wide open. Camera lenses are designed to work with various focal distances. Astrographs only have to work at one focal distance -- infinity.