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old 20x SW eyepiece still useful now that the 25-50x is out there? (1 Viewer)

mbb

Well-known member
The 25-50x seems to be a great eyepiece, but the large field of view of the old 20x SW and the larger exit pupil (for viewing comfort and extra brightness during dull days and dusk&dawn) make me curious. There is not a lot to be read about the 20x SW online in general or here on the forum, and it cannot be found and tested in stores anymore as it is not made anymore.
I was wondering if anyone could share his/her experience comparing both eyepieces?
Does the larger exit pupil make a big difference in brightness and, if so, in which conditions? (mainly at dusk&dawn, or also on cloudy or even bright days?)
What about sharpness? (From the very few comments about it, one or two people seem to have reported a lack of edge sharpness for the 20x, one or two other have said it was great. Thus how good/bad is it? :unsure: )
Does the wider exit pupil and FOV also help for digiscoping?
Did you use or compare them on both the 65mm and the 80mm scopes?

Many questions, but answering any of them is already welcome of course ;)
 
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lmans66

Out Birding....
Supporter
United States
The 25-50 is a much better eye-piece. I haven't compared them side-by-side but have had both. I had the 20-60 eye-piece with a ATS prior to 2013, then a 20-60 eyepiece with an ATM between 2014 and 2016 and then a 25-50 now with my current ATS. All I can say is that there is a 'wow' factor. So given that, I can assume it isn't the scope but the eye-piece.
 

mbb

Well-known member
There was a lot of discussion back here _

Swarovski 20x W Eyepiece and Vignetting​

I have to admit I didn't find that much via the search (maybe I missed something), but I have now found the test digiscoping pictures you have taken, and the advantage of the 20x SW compared to the 20-60x are clearly well illustrated! Thank you! I am still wondering how it fares compared to the wider angle 25-50x zoom.
 

mbb

Well-known member
The 25-50 is a much better eye-piece. I haven't compared them side-by-side but have had both. I had the 20-60 eye-piece with a ATS prior to 2013, then a 20-60 eyepiece with an ATM between 2014 and 2016 and then a 25-50 now with my current ATS. All I can say is that there is a 'wow' factor. So given that, I can assume it isn't the scope but the eye-piece.

Do you mean the 25-50 is a much better eye-piece than the 20-60x zoom eyepiece, or also than the 20x SW fixed eyepiece?
(I am mainly wondering about the quality and current relevance of the 20x SW fixed eyepiece, now that the 25-50x exists.)
 

lmans66

Out Birding....
Supporter
United States
I believe the 25-50 is much better than the 20-60, yes.... For the 20 Fixed...I have no idea as I haven't viewed thru it.

The only thing I would wonder about if I had that 20 fixed is sometimes I do want to get closer. The 50x is very usable so you are missing an entire range of closer-up viewing. Not sure if you are doing Digiscoping or not, but if you do, the 20x power is perfect, or 25 in case of the 25-50. Just thought I would toss that one out.
 

Tringa45

Well-known member
Europe
I have an ATM65 HD with the 30x W, which is a truly excellent eyepiece. It has a 65° AFoV, generous eye relief and is effectively free of rectilinear distotion, field curvature and astigmatism.
Some years ago my dealer had a NOS 20x, which interested me because of the large exit pupil. It was however a big disappointment with limited eye relief, a 60° AFoV, pincussion distortion and, IIRC, field curvature.

John
 

mbb

Well-known member
I have an ATM65 HD with the 30x W, which is a truly excellent eyepiece. It has a 65° AFoV, generous eye relief and is effectively free of rectilinear distotion, field curvature and astigmatism.
Some years ago my dealer had a NOS 20x, which interested me because of the large exit pupil. It was however a big disappointment with limited eye relief, a 60° AFoV, pincussion distortion and, IIRC, field curvature.

John
Thank you for the info!
Was that the latest 20x SW? I obviously haven't look through one yet, but the specs say it should have an AFOV of 68°, practically identical to the AFOV of the 30x SW (but thus of course with a much larger real FOV).
 

Neil

Well-known member
I have to admit I didn't find that much via the search (maybe I missed something), but I have now found the test digiscoping pictures you have taken, and the advantage of the 20x SW compared to the 20-60x are clearly well illustrated! Thank you! I am still wondering how it fares compared to the wider angle 25-50x zoom.
I used to like the 30x the best but these days I'm happy with the 25-50x on my STX85mm
 

Tringa45

Well-known member
Europe
Thank you for the info!
Was that the latest 20x SW? I obviously haven't look through one yet, but the specs say it should have an AFOV of 68°, practically identical to the AFOV of the 30x SW (but thus of course with a much larger real FOV).
I don't recall the exact nomenclature of the 20x but it was outwardly similar to my 30x W of 2011 vintage but more compact. The 30x W was previously described as 30x SW, but when mine was produced the only other eyepiece alternatives were the two zooms, 20-60x and 25-50x.

Are you sure of the 68° AFoV? This would really be at or above the absolute limit attainable at 20x on the Swarovski scope due to the 26 mm sealing "window" in the scope body. Looking for the lowest possible magnification for my ATM65, which would not vignette, I bought a 28 mm Edmund Optiks RKE with a 23 mm field stop. This gives 16,5x magnification but only has an AFoV of 45°. With a 4 mm exit pupil and long eye relief, the views are however very pleasant.

John
 

mbb

Well-known member
I don't recall the exact nomenclature of the 20x but it was outwardly similar to my 30x W of 2011 vintage but more compact. The 30x W was previously described as 30x SW, but when mine was produced the only other eyepiece alternatives were the two zooms, 20-60x and 25-50x.

Are you sure of the 68° AFoV? This would really be at or above the absolute limit attainable at 20x on the Swarovski scope due to the 26 mm sealing "window" in the scope body. Looking for the lowest possible magnification for my ATM65, which would not vignette, I bought a 28 mm Edmund Optiks RKE with a 23 mm field stop. This gives 16,5x magnification but only has an AFoV of 45°. With a 4 mm exit pupil and long eye relief, the views are however very pleasant.

John
I had to do some googling, but found the following info:
- FOV of 3,4degrees or 60m/1000m according to https://www.bhphotovideo.com/c/product/250892-REG/Swarovski_49335_SW_Series_20x_Spotting.html/specs

- the PDF of an old Swarovski catalogue stating 3,44degree or 60m/1000m (thus the same values apart from some rounding of) and an AFOV of 66degrees : http://www.hoferwaffen.com/images/optics/Swarowski_en.pdf

(I still have to know why the AFOV isn’t 20x3,44=68,8 but 66, but that is only a minor relative difference.)

I am not very familiar with optics technicalities and I am interested to understand the reasoning behind your comment about the 26mm sealing window blocking the FOV. I guess you mean that the body of the scope is sealed (against dust, moisture etc.and to keep the gas inside) by a sealing window at the eyepiece side that is not more than 26mm diameter, which limits the maximum feasible FOV with any eyepiece. Is that correct? How do you translate the 26mm (which you probably just measured?) to a maximum field of view and what is the result?
 

Tringa45

Well-known member
Europe
Thanks for posting those links. That is the eyepiece I checked out years ago. Externally it's very similar to the 30x W except that the eye lens is much smaller, which would mean either a narrower AFoV or less eye relief. On the 30x W the eye lens is 29 mm in diameter.

My memory had obviously failed me as regards AFoV. Swarovski's specification says 66°, which I think can be trusted. This is between the ISO calculation of 62° and the product of magnification and TFoV of 69°. I measured 65° on the 30x W using this method: https://www.birdforum.net/threads/a-simple-and-precise-method-of-measuring-afov.359127/.

The sealing window was measured by successively cutting down a strip of paper. The field stop or focal plane of the eyepiece would have to be outside this, otherwise dust on the window could be focussed and consequently the field stop should be less than 26 mm to avoid vignetting.

Astronomical eyepieces with 1 1/4" barrels allow a maximum field stop of 27 mm and two examples are the 32 mm Televue Plössl (50° AFoV) and the 24 mm Televue Panoptic (68° AFoV). These would give 14,4x and 19,2x magnification respectively on the Swarovski and cause some vignetting. The 23 mm Swarovski 20x SW probably places the field stop close to the sealing window and so with a 66° AFoV could avoid any significant vignetting.

John
 

mbb

Well-known member
Thanks for posting those links. That is the eyepiece I checked out years ago. Externally it's very similar to the 30x W except that the eye lens is much smaller, which would mean either a narrower AFoV or less eye relief. On the 30x W the eye lens is 29 mm in diameter.

My memory had obviously failed me as regards AFoV. Swarovski's specification says 66°, which I think can be trusted. This is between the ISO calculation of 62° and the product of magnification and TFoV of 69°. I measured 65° on the 30x W using this method: https://www.birdforum.net/threads/a-simple-and-precise-method-of-measuring-afov.359127/.

The sealing window was measured by successively cutting down a strip of paper. The field stop or focal plane of the eyepiece would have to be outside this, otherwise dust on the window could be focussed and consequently the field stop should be less than 26 mm to avoid vignetting.

Astronomical eyepieces with 1 1/4" barrels allow a maximum field stop of 27 mm and two examples are the 32 mm Televue Plössl (50° AFoV) and the 24 mm Televue Panoptic (68° AFoV). These would give 14,4x and 19,2x magnification respectively on the Swarovski and cause some vignetting. The 23 mm Swarovski 20x SW probably places the field stop close to the sealing window and so with a 66° AFoV could avoid any significant vignetting.

John
It seems that I need to find a good reference with some illustrations to up my technical understanding of scope optics :unsure:
It sounds interesting ànd useful to know and really understand that kind of things :)
For the limited part that I think I already understand, this means that there is the risk that the 20x SW might not fully work on other, Swarovski-eyepiece(fitting)-compatible scopes of other brands for which e.g. the Swaro 25-50x and 20-60x are known to fully work, as those other scopes might not ‘support’ that large of a FOV. Is that correct?
 

Tringa45

Well-known member
Europe
For the limited part that I think I already understand, this means that there is the risk that the 20x SW might not fully work on other, Swarovski-eyepiece(fitting)-compatible scopes of other brands for which e.g. the Swaro 25-50x and 20-60x are known to fully work, as those other scopes might not ‘support’ that large of a FOV. Is that correct?
No, I wouldn't anticipate any problems on other scopes with a Swarovski-compatible bayonet. It shouldn't pose any problems in achieving infinity focus and the worst that could happen might be some vignetting (slight dimming at the field edge) if the sealing window were significantly smaller than 26 mm.

John
 

mbb

Well-known member
No, I wouldn't anticipate any problems on other scopes with a Swarovski-compatible bayonet. It shouldn't pose any problems in achieving infinity focus and the worst that could happen might be some vignetting (slight dimming at the field edge) if the sealing window were significantly smaller than 26 mm.

John
Thank you!
It is a pity there is no way to try the 20x sw except finding some rare one second hand, buying, having it shipped and crossing fingers...
Its larger real fov and exit pupil still tempt me, also as a potential compliment/brother for a wide-angle25-50x zoom eyepiece, for the darker hours of the day (or for dreaming while watching the sky at night :). )
I have found a second hand Kite SP 82 ED = Vogelbescherming Valk HD 83 (according to some, also identical to some Zenray scope) for relatively little money, with the matching 25-50x eyepiece. It should be compatible with Swarovski eyepieces. Upgrading to Swaro’s 25-50x would probably be more than double the price of addingthe Swaro 20x SW and the Kite/Vogelbescherming 25-50x seems already quite good (exxept for its considerable distortion.)
 

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