Few days ago I got one massive Jupiter-21M lens from eBay. It’s 30 years old. Weight is nearly one kilogram. An adapter ring is required to fit it to a camera using Nikon F mount. There are several types of adapters, but the cheap ones without optical element in them work just fine. After adjusting Jupiter’s focus ring, it looks like focusing to infinity is not indeed possible as the eBay seller warned. So focusing is OK to around 50 meters and further that things get really blurry.