pwoah... 3500mm F/3.9 beats my 279 F/6.3
Just imagine what they could do if they pointed it at Jupiter!
That is a stunning shot, and proves the age old saying 'aperture rules'
Mike, it may only be 2hr 19min exposure, but 2hr 19min with 3.5m F/3.9 is more light than ~6hrs with 152mm F/6