I've had a chance to go through and get into order what I’ve collected about the 8x30 Dialyts, so here goes . . .
(I’ve also made a point of indicating where I’m uncertain as to details e.g. there is some useful but not completely clear data about the early Zeiss roof prisms at the Europa website:
http://www.europa.com/~telscope/czpstwr.txt )
The centre focus 8x30 B Dialyt was offered for just over 40 years! - from 1964 to 2004 (in 2005 it was finally replaced by the 8x32 Victory FL)
Versions
There were 3 different body designs:
- the original 1964 long bodied version (see the page from the 1964 catalogue)
- the first short bodied version from 1969, which resulted in a 100 gram/ nearly 4 oz weight saving (see the attached cross section)
- the second short bodied version from 1987 (?), with the diopter wheel located on the front of the bridge
(see the photo comparing versions 3 and 1, from:
https://www.birdforum.net/showthread.php?t=268166 )
In terms of easy visual identification:
- the first two versions had co-located focus and diopter wheels, with the body of the first version being noticeably longer
- and on the 3rd version, in addition to the new diopter wheel location, the rear edge of the bridge angled inwards from the barrels towards the focus knob
Finishes
All 3 versions were available with a leatherette finish, and in addition the 2nd and 3rd versions were also offered in rubber armoured versions
However, judging by the relative numbers of second hand offerings, the RA versions were far more popular than the leatherette ones
Optics
I’ve not been able to obtain the details of the optical construction of the 1st version but there is no reason to imagine that it was more sophisticated than the later versions
- or that it was airtight
The optical construction of the 2nd and 3rd versions is the same - see both the cross-section that I posted of version 2, and that of version 3 provided by Henry in post #3 above
As noted previously on this thread, the design used external focus by movement of the objective lens pair
(this is in contrast to an internal focus system, where the physical length of the optical system - from the front objective lens to the rear eye lens - remains constant during focusing)
continued . . .