Hi Dennis (post #24),
While the Dialyts are a classic external focus pump action, they don’t seem to be susceptible to environmental contamination
I’ve previously posted about an article by the late ornithologist Francois Vuilleumier ‘Are Zeiss binoculars the preferred instruments for birdwatching?’
It’s from the Zeiss Historica Journal, Spring 2007 edition. See from page 13 on at:
https://www.mikeeckman.com/2019/11/zeiss-historica-spring-2007/
In itself it’s interesting to read a detailed discussion from an earlier era, about what were then the start-of-the-art binoculars for birding
However, Francois also describes his extensive use of the 7x42 Dialyt under extreme environmental conditions. See the last paragraph in the first column on page 19 of the extract
Part of the reason for the Dialyt’s relative imperviousness may have been because like their Porro counterparts, they were fitted with seals
In 1956 Zeiss West Germany added the seals to their newly introduced Porro line. See an image from a 1964 catalogue with the seals indicated in red
So it wouldn't be surprising if Zeiss West had taken similar steps with the Dialyts (in fact it would have been surprising if they hadn’t)
Perhaps Gary/ garymh can offer further insight?
John