The Sky-Watcher HAC125DX Mini Astrograph is an exciting upgrade from the original HAC125. This small but powerful scope brings together an incredibly fast f/2 focal ratio, a compact form factor, and sharp optics for anyone looking to dive into EAA or dedicated astrophotography. In this review, we’ll take a closer look at its specifications, performance in the field, and things to consider when imaging at f/2.
Overview & Key Specifications
The HAC125DX is a Honders-Advanced Catadioptric optical design and features:
- 125mm primary objective
- 250mm focal length
- f/2 focal ratio
- 16mm image circle (more on this below)
- 8.4 lbs total weight
The HAC125DX is a light and compact system designed for widefield astrophotography and is perfect for pairing with smaller equatorial mounts like the Sky-Watcher AL55i. This combination makes for an incredibly lightweight imaging rig, ideal for anyone seeking an ultra-fast, ultra-portable setup. When cameras like the or ASI533MC Pro are paired with the short focal length of this scope, larger deep-sky objects like the Andromeda Galaxy will fit comfortably in your field of view.
Camera Compatibility
The HAC125DX has a 16mm corrected imaging circle and is designed for puck-style planetary cameras like the ASI178MC or ASI676MC with small pixels. However, cooled astronomy cameras with smaller sensors—like the ASI533MC or ASI585MC—also pair quite well with this scope for users with a dedicated astrophotography setup in mind.
This scope comes with three different camera adapters, allowing use with cooled cameras, puck-style cameras, and mini-style guide/planetary cameras. We tested both types of cameras for this review—results below!
Things to Consider When Imaging at f/2
Imaging at such fast focal ratios can be extremely rewarding, especially when clear skies are limited. Shooting at f/2 allows you to collect a lot of data in a short time, giving you great results in a single night under the right conditions. Fast focal ratios also gather more light than slower systems of the same aperture.
Most popular cooled cameras today have small pixels, which pair well with this scope to deliver impressive detail. That said, imaging at f/2 does require extra attention—factors like collimation, focus, and tilt will affect star shape and image quality more than with slower f/4 Newtonians or f/6 refractors.
The HAC125DX does come factory-collimated, but double-checking collimation before a session and refocusing every couple of hours will give you the best results. And don’t forget—every good dataset needs a solid set of flat frames.
Using Flat Frames with the HAC125DX
Flat frames are essential for eliminating vignetting and unwanted artifacts. Because the camera and USB cables sit in front of the main optics, placing an LED panel flush against the dew shield is only practical with the smaller puck-style planetary cameras.
When using a cooled camera, you can try positioning a flats panel a few inches above the scope, but it must be large enough to evenly illuminate the aperture. This can be tricky in the field. For this review, we used the classic T-shirt method, which consistently gives us great results: simply stretch a white T-shirt or pillowcase tightly over the front of the scope and camera, then secure it with rubber bands. Make sure the fabric is smooth and wrinkle-free to ensure even illumination.
Field Test and Data Analysis
Our team at High Point is full of dedicated astrophotographers, and we wanted to push this scope to its limits using a cooled camera—the ASI585MC Pro. We targeted the Elephant Trunk Nebula, a stellar nursery in Cepheus that’s a favorite among amateur imagers.
Gear Used:
Under Bortle 4 skies in the countryside, we captured 5 hours of total exposure.
We had solid results with the ASI585MC Pro. We did notice minor focus shifts and some sag in the imaging train, likely due to the camera’s weight and sensor size. Tightening the front thumbscrew helped reduce tilt, and the helical focuser performed smoothly. With a bit of PixInsight deconvolution, we cleaned up the stars and captured a solid image of the Elephant Trunk—no filters used.
Switching to the lighter ASI178MM significantly improved star shapes. The reduced weight and smaller sensor made a noticeable difference in image quality. This confirmed the scope is optimized for smaller, lighter cameras, though it can still perform well with cooled setups. For a full data breakdown, check out our video review here.
Final Thoughts
All that said, the HAC125DX is a fantastic option for anyone looking for a portable, ultra-fast astrograph that works even with the smallest equatorial mounts. If you're into EAA and live stacking, its fast optics will give you impressive real-time results. And if you want to use it for dedicated astrophotography, that’s definitely possible too. You’ll just need to make a few small adjustments to collimation and refocus more often due to the incredibly fast optics—but don’t let that stop you, because we were still able to get some pretty awesome results in a single night.
Learn More
Interested in diving deeper into the world of astronomy? Check out our Astronomy Hub for a wealth of articles, guides, local resources for planetariums and observatories near you, and more to enhance your stargazing experience.
