I have two of these for Konica, white & red lettering and white & green lettering, one for Minolta MC and one for M42. Some years ago I wrote about this lens, the 19/3.8 and the 21/3.8 T4 in Camerashopper. The 20 is my favorite and seems to be the sharpest of the three. The older 21/3.8 T4 model is a very close second and surprisingly good. The 19 is not bad when stopped down a little and is light and compact but it is not as good as the other two. I have that lens in Canon FD mount. I remember using the 20 with a Konica at the ballpark when the previous Yankee Stadium was new. The 20 and 21 are similar in appearance to the 21/4 Konica Hexanon and the 20/4 Zeiss Flektogon. My 21/2.8 Hexanon is much smaller and lighter but the big 20 is still fun to use.