Archived posting to the Leica Users Group, 1997/11/04
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Adi - It is still a controversial subject, since at first Leitz denied ever using radio-active Thorium in their glass to make the early 50/2 Summicrons with s/n under 1,000,000. It is now common knowledge that they and Hassleblad & others did. Dr. Cyril Blood in the UK was one of the first to write about this in the LHS Newsletter. With age, this glass turns yellowish brown & will show on Chromes. Bill Gordon & I followed up on Dr. Bloods request for info and found that I had 2 of them in my collection and Bill had 3. Checking them with a sensitive Geiger counter, Bill found that neither his nor mine exceeded 2.5 mili-roentgens on the front element & 1.5 m.r. on the rear; no where as near as the old radium watch dials of the 1950's and would take about a week in the dark on top of a piece of film, to leave an exposure. All this, and photos also, were written up less than a year ago in the LHSA's Viewfinder. There was one other type of so called "yellow glass" that Alf mentioned in regards to soft & hard coating of the Summicrons; that was a very soft magnesium flouride coating that was used for awhile but was discontinued by Leitz in favor of the harder magenta coating. All the Leica lenses that I have had polished & recoated by John van Stelten have had this hard coating. Marvin Moss ======================================================= In a message dated 97-11-03 12:53:56 EST, you write: << I looked through my 50 f/2 lens at a white piece of paper and found that there was a strong yellow cast to the image. I tried this also with an 80mm Planar for Hasselblad and it too had this yellow cast. Is such an occurrence normal ? --adi >>