A 125mm (5") Honders Advanced Catadioptric Astrograph

[JayTee]

Has anyone yet heard of the Sky-Watcher HAC125DX f/2 Minigraph Astrograph? At $995 from Canadian - All-Star Telescope, it deserves serious consideration.

Anyone?

Here's a link to some info
https://www.skywatcherusa.com/products/ ... 5e70&_ss=r

[JayTee]

So here's what I found out about this optical design by referencing Amateur Telescope Optics (aka the telescope bible) sec 10.2.1.3.

The Honders design optical system has three elements: the front corrector lens, the rear "second" surface mirror, and a third catadioptric lens in front of the corrector lens. This is a take-off of the 1814 Hamilton catadioptric design which was the first catadioptric dialyte. The dialyte design is a compound lens design characterized by widely air-spaced lens elements, used to correct optical aberrations and save on glass material, especially when the elements have dissimilar curvatures.
The Honders design (from Klaas Honders circa 2000) uses a relatively weak positive front lens - a direct consequence of using the same type of glass for both elements - also in combination with a widely separated catadioptric element (CE). The third element is a small positive lens, a short distance in front of the final focus. Also, the Honders design has all of the aberrations minimized to negligible, or near-negligible amounts by making relatively small adjustments in radii and separations. The secondary spectrum is at the level comparable to an f/70 standard achromat and can be further reduced by a factor of 3 with a few minor tweaks.
Here's a link to the page in ATO site: https://www.telescope-optics.net/honders_camera.htm

The problem I'm having with this OTA is that the FL (250mm) is so short that it becomes a "specialized astrograph" used for only the very largest DSO's. The graphic below shows that even M31 doesn't fill the frame using this OTA and the ZWO ASI 294MC Pro camera.

But the design is so interesting that I'm struggling to say "no" to this purchase!

In case you wanted to know: The term "catadioptric" comes from "catoptric" (relating to mirrors) and "dioptric" (relating to lenses). So, catadioptric systems use a combination of lenses and mirrors to focus light, offering advantages like compact designs and good image quality.

[Gordon]

Strange design.

I would like to see some reviews before I would spring for it.