If you want a lot of reach on X-mount and don’t mind donut bokeh then you really can’t beat the value of the Tokina 400mm + 2x Extender on Amazon which will give you 1200mm of reach on an APS-C camera. I currently own the Tokina 400mm and I am very impressed with its performance and weight. I plan to pick up the 2x TC as soon as it is listed on its own by a US retailer because it is only listed by Amazon UK at this time.