Hey there Glen.
I have experimented with camera lenses for astrophotography and i found 2 distinct disadvantages
1st is the star distortion due to the non circular shape of the diaphragm.
2nd is the pita to focus. I jimmied up a belt driven system using my moonlite focuser motor but it was not consistent.
Other things to consider is if a zoom lens is used the lens elements component moves around in the lens itself thus affecting the orthography of the sensor plane. (Hope i used the right word there!
)
Having said all that i was using a sigma 150-500mm lens at 500mm. So these distortions were quite evident. Maybe not so much at shorter fl like 50mm.
My 5c.
Scott