Dear Customer, it could support a 150-600 mm lens but need a adapter to maintain the balance. 

Equipped with eyepieces: H6mm, H20mm The multiples are: 300/6=50 times, 300/20=15 times. If you choose a 3 times Ballov lens, the magnification is 50X3=150 times, 15X3=45 times; plus a 1.5 times orthographic lens, the imaging is a positive image, and the magnifications are: 50X1.5=75 times, 15X1. 5=22.5 times. Namely: minimum magnification: 15 times, maximum magnification: 150 times. 

That may be caused by the fact that the lens weight is much bigger than camera, If used your telephoto lens with our adapter ring, we suggest to use with a lens bracket and better to shoot on a tripod to increase its stability. 

The longer Flange distance lens to the shorter Flange distance camera, then could use the infinity focus.
but if the shorter Flange distance lens to longer Flange distance camera, then could not use the infinity focus, you can focus on a limited distance.
the position of the infinity mark 【∞】of the telephoto lens or super telephoto lens is shifted slightly to the positive side to enable focus adjustment even when focus shift is caused due to temperature changes.The shift range is denoted by an L-shaped line, Be sure to check the focus through the viewfinder even when you shoot at infinity. 

Yes, just make sure if you use a large lens use the lens' tripod mount. If not it may topple. But the tripod is sturdy.