Hi BB,
For a lot more info than you need! (and hopefully of general interest to some) . . .
A) The x50 SLC line was introduced in 1997 in 7x50, 8x50 and 10x50.
The latest 7x50 that I’ve seen dates from June 2009 (#D7923 79855); the latest 8x50 from July 2007 (#D7727 60834), and;
the latest 10x50 from December 2010 (#D8050 88642).
(In contrast, the original x56 line continued until 2013, when it was replaced by the all new x56 design that’s still in production)
B) As indicated by MBB in post #2 above, the link that he's provided gives various details about the x42 SLC’s.
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Coatings
In comparing a 2003 unit to a 2008 one - if you were to do a direct comparison by stacking one on the other - you’d probably see that the latter was slightly brighter and the image slightly more neutral. However, whether the difference would be significant in use is highly unlikely.
For a rough idea of transmission differences, see a graph from Gijs comparing three 8x30 SLC units: a pre-Swarobright one from 1998; a Swarobright coated one from 2003, and; a nue/new one from 2005. As can be seen there’s at the most a 5% transmission difference between the last two.
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x50 Optical Construction
I) Objectives
The objectives of the x50’s and x42’s have the same number of lenses. However, they are in a different order.
The x50’s have an initial doublet, followed by a single focusing lens, while the x42’s reverse the sequence.
See two images from Swarovski. The first from a 2000 catalogue shows what may be the 10x50. See Henry’s comments in post #246:
The new 8x30 CLl's
And the second from a 2005 catalogue is of a 7x50.
For ease of comparison, see a 7x42 image that’s in addition to the one in the link provided by MBB.
II) Eyepieces
The x50’s have a simpler eyepiece of 4 lenses in 3 groups, in a 2, 1, 1 sequence (vs the x42’s use of 5 lenses in 3 groups in a 2, 1, 2 configuration).
On the three x50 models, magnification is varied by altering the shape, thickness and spacing of the lenses. However, the details of the differences are not particularly clear in the two images from Swarovski.
Fortunately, there are a number of images of actual x50 units that have been cut open to show the optical construction. The problem is that many seem to be inaccurately marked as to whether they’re 7, 8 or 10x.
Jan has indicated that a specialist German firm does the work for most companies (using a high pressure water jet?). The units may have been stripped of removable parts before shipping off for cutting, and then reassembled on return. So perhaps the miss marking occurred when the focuser knobs were reattached?
For the details of the three different eyepieces, see a cropped/ composite image, that presumedly correctly shows from left to right:
the 7x50, the 8x50 and finally the 10x50.
The first part is from a full length image at:
Swarovski Optik
The second is from a 2014 eBay listing from canadiansportsoptics
The third is from a full length image from JG at:
A new Swarovski NL Pure? - Page 10 - Binoculars - Cloudy Nights
(as JG indicates he obtained the image from a vendor, and after discussion we agreed that based on it's proportions the unit is a x50 one)
And also see a full length view of what should be the 8x50. It’s from a 2020 eBay listing by ffordesphotographic.
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Specifications
Finally, for a comparison of features see a page from a 2005 catalogue that includes the SLC lineup.
John