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New Svbony 2 inch 99% dielectric diagonal (SV223)

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#1 AdAstro

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Posted 18 September 2023 - 11:49 PM

I recently obtained one of the new Svbony SV223 2" dielectric diagonals and wanted to share my (limited) experience so far. And to be fair, this is my first 2" diagonal. I've been interested in getting a 2" diagonal for quite some time to try both on my refractor (AT72edii) and my SCT (C8).

 

Full disclosure: Svbony provided me a sample to try for free. What follows is my honest assessment.

 

First, the specs. Svbony claims the mirror is 99% reflectivity and 1/10 wave accuracy. It comes with a pretty standard (though nice quality) 2" to 1.25" adapter with compression ring and a 2" nosepiece. What makes this diagonal stand out is the twist lock mechanism on the 2" eyepiece side. More on that below. The diagonal currently sells for $150 on Amazon.

 

https://www.amazon.c...e/dp/B0CFQBZWJM

 

My thoughts so far:

 

- Build quality is great. The diagonal has a nice weight to it. Most everything is metal on this piece, with the exception of the side pieces, which are plastic on my copy. Some of the marketing material from Svbony claims these sides are carbon fiber. Maybe that is true of other production runs but not here.

 

- I was quite pleased to find that the 2" nosepiece can be removed to expose M48 threads. From what I understand, M48 threads are common on many 2" diagonal bodies, but not necessarily a given. This makes it simple to adapt the diagonal to SCT threads with an M48 to SCT adapter (available from a variety of sources: Astromania, WO, etc.). I was hoping this to be the case given that I wanted to also use this on my C8

 

- Ultimately, I adapted the diagonal body from the native M48 to M42 with a M48 male-M42 female ring and then attached my Meade variable CCD T adapter. The Meade T adapter is essentially one very short SCT-M42 adapter with a few different length T2 extensions. This allows you to customize the optical length as desired. In my case, using just the short adapter alone, I can keep the optical path fairly short so as not to extend too far beyond the C8's optimal backfocus length. (I'm also hoping this will let me use the diagonal with my f/6.3 focal reducer/corrector)

 

- Speaking of optical length, the Svbony product page states 109.1mm optical (and 118.6mm with the 2" to 1.25" adapter). My rough measurements say these numbers seem pretty close to actual.

 

- Last, the twist lock. Like I said, I think this is the standout feature. Now, the Svbony marketing description calls this a "click lock", which it is not. You do have to twist roughly 60 degrees to secure/unsecure an eyepiece and there is no "click". But I don't particularly care here. The mechanism is fantastic. Twisting is very smooth and the hold on the eyepiece feels quite secure. Granted, this is my first experience with a twist lock, but I am quite happy with the function. There is also a small set screw to lock the ring in place to prevent rotation.

 

 

In a few days, I hope to post my observations and comparison to the other diagonals I have on hand: another Svbony 99% dieletric with no stated flatness spec (SV188P) and the venerable Celestron 1.25" prism diagonal. More to come.

 

And if any more specific questions/info desired on this diagonal, feel free to post.


Edited by AdAstro, 18 September 2023 - 11:54 PM.

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#2 AdAstro

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Posted 18 September 2023 - 11:52 PM

Side view

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Edited by AdAstro, 18 September 2023 - 11:55 PM.

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#3 AdAstro

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Posted 18 September 2023 - 11:52 PM

Looking down the mirror

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Edited by AdAstro, 18 September 2023 - 11:53 PM.

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#4 AdAstro

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Posted 18 September 2023 - 11:54 PM

With SCT adapter (my own, does not come with the diagonal but easily done with M48 threads on diagonal body)

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#5 Avgvstvs

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Posted 19 September 2023 - 03:06 AM

A nice review. Thank you



#6 ares53405

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Posted 19 September 2023 - 07:40 AM

It should work with your C8 but it might not work with your AT72EDII.  You can read about more about it here under "Product Description"...

https://www.astronom...refractors.html


Edited by ares53405, 19 September 2023 - 07:41 AM.


#7 AdAstro

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Posted 19 September 2023 - 08:48 AM

It should work with your C8 but it might not work with your AT72EDII.  You can read about more about it here under "Product Description"...

https://www.astronom...refractors.html

Thanks very much! Svbony one indeed looks like a rebrand of that AT diagonal. I will find out soon enough about eyepieces in the AT72edii and will report back. I guess it depends on when your AT72edii came out of the factory. 

 

Here is another thread for those interested: https://www.cloudyni...e-difficulties/



#8 ares53405

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Posted 19 September 2023 - 11:05 AM

If it doesn't reach focus in your AT72EDII but it's close, you could try using a "Tele Vue 2" to 1.25" In-Travel Eyepiece Adapter".  You'll gain quite a bit of in focus with one of those.


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#9 donniesoprano

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Posted 19 September 2023 - 01:41 PM

Yes, the rotating visual back pushes the focal plane out just a little bit further on the 72EDII.  This leads to issues with some diagonals/eyepieces, binoviewers, etc.  That said, I think the 'target' use case for the 72EDII is imaging, but that didn't stop me and many others from buying one for visual.

 

ds



#10 AdAstro

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Posted 19 September 2023 - 09:20 PM

If it doesn't reach focus in your AT72EDII but it's close, you could try using a "Tele Vue 2" to 1.25" In-Travel Eyepiece Adapter".  You'll gain quite a bit of in focus with one of those.

Thank you. That is a good tip. 
 

 

Yes, the rotating visual back pushes the focal plane out just a little bit further on the 72EDII.  This leads to issues with some diagonals/eyepieces, binoviewers, etc.  That said, I think the 'target' use case for the 72EDII is imaging, but that didn't stop me and many others from buying one for visual.

 

ds

Agreed, it is great for visual as well. Seems like it was a slip up at the factory for a certain period of time during production.  



#11 AdAstro

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Posted 19 September 2023 - 09:29 PM

All in all, the Svbony diagonal is a nice accessory, assuming that you can accommodate the optical length. The twist lock is well worth it if so. 
 

That said, if this is simply a rebrand that is identical to the AT 2” diagonal, which it appears it is, Svbony will have to make it more cost competitive. Right now, the SV223 is at $150 new while the AT diagonal is selling for $130. 
 

Perhaps Svbony could consider bundling in some other add ons to make this more compelling. For example, an SCT adapter would be a no brainer. Perhaps a twist lock 2” to 1.25” adapter to extend the twist lock function to our 1.25” eyepieces. 



#12 AdAstro

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Posted 20 September 2023 - 11:39 PM

Returning to report that I can get my 1.25” eyepieces to come to focus in my AT72edi with a few mm to spare. I had about 9mm of in travel left with a 24mm UFF and 5mm with an Svbony 9-27mm zoom (which sits up high in the diagonal itself). I guess I have one of the corrected versions of the scope. Initial quick look through the diagonal showed nice images. 


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#13 therealdmt

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Posted 21 September 2023 - 03:44 AM

Returning to report that I can get my 1.25” eyepieces to come to focus in my AT72edi with a few mm to spare. I had about 9mm of in travel left with a 24mm UFF and 5mm with an Svbony 9-27mm zoom (which sits up high in the diagonal itself). I guess I have one of the corrected versions of the scope. Initial quick look through the diagonal showed nice images. 

Glad to hear it’s working out for you.

 

I’m guessing that the zoom sitting high in the diagonal is due to it resting on a shelf/aperture stop within the eyepiece-side port of the diagonal that prevents things (eyepieces, barlows/filters, etc.) from being inserted too far and contacting the mirror, is that correct? 
 

That happens for me with my ES 2x focal extender and one of my diagonals — can’t be inserted all the way in



#14 AdAstro

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Posted 21 September 2023 - 10:33 AM

Glad to hear it’s working out for you.

 

I’m guessing that the zoom sitting high in the diagonal is due to it resting on a shelf/aperture stop within the eyepiece-side port of the diagonal that prevents things (eyepieces, barlows/filters, etc.) from being inserted too far and contacting the mirror, is that correct? 
 

That happens for me with my ES 2x focal extender and one of my diagonals — can’t be inserted all the way in

Thanks! I didn't explain that very well. The zoom has a "shelf" of sorts on its own barrel and that seems to make it sit up a little higher than other eyepieces I have requiring a bit more in focus travel. Here is a picture of it (different branding, but same zoom).

 

I am curious how my 2x focal extender will work out though now because I think it may be similar to your ES one.

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#15 AdAstro

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Posted 02 October 2023 - 11:07 PM

All, wanted to give some updated impressions after some time with this diagonal. It now lives pretty much permanently attached to my C8. I have quite enjoyed the secure connection of with the SCT adapter that I added on. And making this extension very short affords enough backfocus to still use my f/6.3 reducer-corrector. So I can basically get the best of all worlds: either 2" eyepieces or the reducer (or both if I really want to over-extend the TFOV of the C8). 

 

Optically, I've found the diagonal to be a good performer. First thing I checked was collimation and it appears to be spot-on. No change with or without the diagonal. Of course, that may vary from one to the next, but it least is a good start. My cheaper 1.25" Svbony dielectric has some slight mis-collimation and no easy way to adjust it.

 

Now, I'm probably not too discerning of an observer but I've found views to be bright and sharp. I am quite happy with its performance. It is at least on par with my other diagonals, if not better. My main targets tend to be star clusters and those are quite pleasing. Less than ideal seeing has limited my planetary observing, but occasional views of Saturn have also been highly satisfactory.

 

Regarding barlow/focal extender, I had no problem fully inserting my Svbony 2x 4-element telecentric barlow (https://www.svbony.c...nt-barlow-lens/) into the diagonal. No interference.

 

In all, I can certainly recommend this diagonal if you can get your hands on one.



#16 HYQID

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Posted 07 October 2023 - 04:12 AM

1/10 lambda,doubt it.



#17 AdAstro

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Posted 11 October 2023 - 02:29 PM

1/10 lambda,doubt it.

For what it's worth, other resellers of this particular diagonal quote the same thing. I haven't seen testing though.

 

https://www.stellarv...nal-2-d1028ecf/

 

https://www.astronom...refractors.html

 

I suppose the mirror could get swapped out for something of different quality depending on what the reseller requests. The Apertura variety actually quotes a 1/12 wave mirror.

 

https://www.highpoin...r-diagonal-d2cf


Edited by AdAstro, 11 October 2023 - 02:29 PM.



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