Having read the reviews which were reasonably good I invested all of £102 in a JINTU 420-800mm zoom lens. Obviously at this price it is very basic. Manual focus, fixed apature which varies from F8.3 at 420mm to F16 at 800mm. I wanted it for photographing the Moon or Sun. Here it is fitted to my Canon 70D on its first try out photographing the Moon.
I took severa photos as the manual focus is tricky to get spot on. This is a full frame shot (no cropping)
That wasn't the best focussed shot but the one with the Moon nearest the centre of the shot.
A crop from a slightly sharper photo:
Obviously not as sharp as the Canon £1000+ 800mm lenses but I think it's very good for the price. It has a standard M42 thread and comes with an adapter to match your camera. Needless to say it has to be on a sturdy tripod and the camera operated by a remote of one sort or another. The slightest movement will blur the image.