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.
