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CTS 85 eyepiece compatibility (1 Viewer)

All the info I seem to find suggests that the CTS 85 only works with the 25-50 or the 20-60 but I'm wondering why it wouldn't work with the 30SW, given it's the same fitting.

Have I missed something?

Thanks in advance for any info.
 
I see no reason why it shouldn't. The bayonet fitting is the same as on the ATM/ATS and STM/STS scopes.
I have a 30x W (2010 vintage) on my ATM 65HD and am not the only one here on birdforum to consider it the best eyepiece ever made for a spotting scope. Just like many other fixed focal length eyepieces it was unfortunately discontinued some years ago. Good luck in trying to find one!

John
 
I see no reason why it shouldn't. The bayonet fitting is the same as on the ATM/ATS and STM/STS scopes.
I have a 30x W (2010 vintage) on my ATM 65HD and am not the only one here on birdforum to consider it the best eyepiece ever made for a spotting scope. Just like many other fixed focal length eyepieces it was unfortunately discontinued some years ago. Good luck in trying to find one!

John

Thank you. Is the 30 W the same as the 30 SW?
 
Thank you. Is the 30 W the same as the 30 SW?
Andrew,

It's probably just a difference in nomenclature, but perhaps the optics historian, John Roberts could chime in here.
I think my eyepiece labelled 30x W was the last version produced. It has an eye lens 29 mm in diameter and so much eye relief that, as a glasses wearer, I extend the eyecup a little. There are, however, none of the viewing problems some report with the 25-50x zoom.
Swarovski used to produce 20x and 45x fixed focal length eyepieces and some years ago I tried out a NOS 20x at my dealer's. It had rather limited eye relief, a 60° AFOV (65° on the 30x) and, IIRC, noticeable pincussion distortion and field curvature.
At least on the 65 mm objective the 30x W is essentially free of field curvature and astigmatism. In these respects the combination is even better than my 10x42 EL SV.

John
 
Hi Andrew,

The CTS draw tube telescope and the ATS/ STS fixed body telescopes, all have the same eyepiece mount and objective focal length
So the same eyepieces fit all of them and have the same magnification

The S series eyepieces were introduced in 2002 with the new ATS/ STS scopes that replaced the earlier Porro prism AT/ ST ones introduced in 1990
Unlike the earlier AT/ ST eyepieces, the S series ones are waterproof


For reference I’ve attached various specification sheets:
• From an AT/ ST manual from 1990 showing the original/ pre-S eyepieces *

• From the 2005 catalogue the S series eyepieces
- both the table and the text mention that they are watertight
- and as can be seen from the spec’s the 30x and the 20-60x differ optically to the original versions

• From the 2011 catalogue, by which time the S designation is no longer included
- and the 20x has been discontinued and the 25-50x added


* for quick visual identification, the original eyepieces have fixed rubber eyecups while the S series have twist adjustable ones; and
- the original eyepiece serial numbering has an H prefix
- while the S series serial numbering has a V prefix


John
 

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Thanks for posting those specifications, John. So it seems the "W" was just an interim measure to differentiate from the old AT80/ST80 eyepieces.
Btw, I don't understand those specs for waterproofness. They look like a mishmash of imperial and metric units. Similarly they got confused with the FOV specifications on the ATM/STM scopes, having got it right on the original ATS/STS scopes, and the 60 m FOV of the 20xSW translates to 62° AFOV.

John
 
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