Not a question but a report on some experiment! I have used a Topcon Fluorite LF Converter 150-300 on my Apo-Symmar 150 mm for 4x5 shots. Recently, I purchased a 300 mm so this item has become obsolete to me. But I thought of a new use for it and mounted it on a 210 mm f6.1 Xenar thanks to a $3 stainless steel cylindri cal box from Ikea, drilled both ends and black coated inside. The focal obtained , although it will vary from the distance the converter is placed from the lens, is equivalent to a 600 mm with great image circle and the loss of luminosity is 3 stops. Colors are perhaps very slightly affected, compared to my Apo-Ronar 36 0 comparison shots but truly nothing to worry about. Bellows extension is around 40 cm. The slides I have made with this combination are as contrasty as they wo uld be if made with a good lens. They look sharp on the light table when viewed with a 3X loupe, nearly as sharp as the slides made with the normal 150-300 mm s et. But of course, when viewed with a 10X loupe, the miracle stops here! (althou gh I have no idea of how sharp slides made with a good 600 mm would be, stabilit y factors being critical). Taken at f22 (f64) the images under my eyes would mak e very decent 8x10" prints for sure. Perhaps would it be worse carrying a test o n different lens openings. But in one word, interesting if you already own both components. Lets you perhaps evaluate before the purchase of the "real thing". N ow please, doctors in optics and fine lens worshippers, don't get me wrong and d on't throw stones at me !!!