Suggestions for old 400mm+ lens for NEX?

Cheap lens ?
I got two suggestions for you, on the (very) cheap side :

• mirror lens : i bought a (50€) 5.6/300mm makinon mirror lens. It's not a great lens. I call it my low contrast lens, because it really is. But it has good sharpness, is very light and very convenient to carry. It is a lot of fun to use on sunny days ! Plus you can use it handheld with a little practice :

• have you ever thought of trying a lens doubler ? I bought one Tokina (7 elements) for 10€ ! Set it on the back of my Zuiko 100/200mm zoom (another 20€ !) and here you have a cheap and fun 400mm lens (600mm equivalent on 35mm camera !). Very slow, a little tricky to get good focus, but you can use it with many different lenses. It gives great results on my zuiko 135mm :