These tubes are very useful for outer bay lenses because the lenses were designed many years ago when close focusing was not a priority with designers. As with the outer bay lenses, the tubes exhibit some of the same problems. They are difficult to use at first until you get used to their peculiarities. They work like the attachment ring that comes with the outer bay lenses. There are two tubes in the set and are meant for the Takumar 400, 600, 800 and 1000 mirror lenses. I feel that the flange on these tubes is a bit too narrow to get a good grip on. This makes it difficult to remove the tubes from the lens and body at times, thus slowing down the photographer. But, you don't want to attach the lens/body too loosely with these tubes either; this could cause the lens/body to fall off. With 600mm, the close focus distance is about 14 feet w/ both tubes. Still not enough for small birds but great for small mammals. Close focus w/ the 400 is 9 ft. With the 800 it is 25 ft. With the 1000mm it is about 40 ft. Overall, these are nice tubes but do require some learning curve. SR

-- Steve Rasmussen (srasmuss@flash.net), May 06, 1999