Almost 1 year later, I can kind of answer my own question about the “old” CT-75 and 20x SW:
(A very friendly fellow forum member sold me his 20x S W some time ago. More recently, I found a CT-75 with original 30x ww eyepiece (thinner, with fold back eyecup) for a very good price online.)
I just tested it at home: the 20x S W fits perfectly on the CT-75 and gives a nicely sharp view. Thus I have no idea why Swarovski mentioned only the 30x S W specs with it, but not the 20x S W specs. (Though I would like to, I don’t have the 30x S W. Thus below, I’m referring to the original 30x ww.)
The 20x S W gives a wider real field of view compared to the 30x. It also results in a way more stable view than with the 30x when using hand-held (yet still wobbly). All as expected and hoped. Both eyepieces are very sharp.
The newer design 20x has a considerably larger outer housing diameter (and larger glas on the eye/user’s side). But it appears to match the base of the CT-75 (likely that was on purpose) and thus it fits well also externally. However, the long rubber eyepiece-protector that you can put over the 30x eyepiece to protect it, is too small to fit over the 20x. Thus another cap or protector is needed. That’s all.
I am actually quite impressed with the view through the scope: I didn’t know what to expect from a draw tube scope, and this one is around 25 years old, second hand. Based on the serial numbers (adding 30 to the first two digits), the scope and 30x eyepiece both date from 1999, and the 20x SW from 2002. At first sight, all 3 optics are still in pristine conditions (of course small, actually very little signs of use to the exterior housing, but that is just cosmetics).
The first time, it is strange to hear that kind of « pumping » sound when extending/collapsing the scope, but the decent resistance when doing so and the lack of any dust inside seem to suggest that the rubber joints are still doing a very good job.
While I’m impressed by the nice view this scope and eyepieces still give, I’m not sure yet that I can make good use of the draw-tube scope, holding it stable enough. I didn’t buy it to use it on a tripod (I prefer an angled scope for that). I’m curious of how it will fit as a companion when doing my regular tour with the bike. I like my 50mm MM4 Opticron with compact tripod and 23x eyepiece as lightweight option, quite easy to put in and out of my cycling bag. It is my current scope companion when with the bike (actually the scope I used most of the time now), but as I rather often cycle in the evening and days are getting shorter, I’m curious of what this 20x75mm could do, with the much larger exit pupil, handheld or maybe with a monopod. It is still quite heavy and it would be more stable to use if the weight was distributed more towards the rear (towards the user). The 20x already helps compared to the 30x, but I still have to try it out on the field. Hopefully this weekend already
