“On a Moon-free night from my favourite Bortle class 3 rural location in mid-Norfolk, the 13028HNT and an unfiltered Canon 550D camera taking three-minute exposures at ISO 800, revealed eighteenth-magnitude stars in the vicinity of the Andromeda Galaxy.
Furthermore, plate-solving the Canon’s 5,184 × 3,456 -pixel images revealed a true field of 3.54 × 2.36 degrees.
Therefore, the review astrograph had an actual focal length of 361mm and a resolution of 2.46 arcseconds per pixel (the Canon 550D has 4.3 micron-sized pixels).
Star images were pin-point sharp to the extreme corners of APS-C sized frames, too."
Review by Ade Ashford writing for Astronomy Now (pdf)
About this product
Model: sharpstar_13028_hnt_blue
Part Number: 13028HNT-Blue
This new 13028HNT model has the same super-fast f/2.8 focal ratio as the larger 15028HNT, but a slightly smaller aperture.
The hyperbolic primary mirror design produces sharp, round stars within the 44mm, full-frame imaging circle.
The primary mirror is made from low-expansion PZ33 glass and dielectric multilayer coatings that increase reflectance to 97%.
Compared to a focal ratio of f/4, the 13028HNT attains the same image quality with almost half the exposure time.
In addition, the compact design provides excellent portability for those who travel to dark-sky sites.
The minor axis of the secondary mirror is 65mm, so it provides sufficient illumination for full-frame imaging. It is worth mentioning the corrector design is a two-refractive lens set, one of which is an ED glass.
The telescope tube material is carbon fibre material to reduce weight.
All metal components are CNC-machined, and the tube rings feature cut-outs that reduce overall weight.
The 2.5" dual-speed Rack & Pinion focuser features coarse and fine focus adjustment with easy-grip knobs.
The focuser is tapped with an M63 thread which can be switched into a more general M48×0.75 thread with an included adapter ring. This gives the user a wider range of options when connecting astronomy accessories.
Back-focus is the usual 55mm (from the base of the mounting thread, on the adapter ring’s housing).
A versatile handle and Vixen-style dovetail plate are also included.
Review by Ade Ashford writing for Astronomy Now (pdf)
Specifications
- Aperture：130mm
- Focal length of primary mirror：364mm
- Focal ratio of the primary mirror：f/2.8
- Primary mirror type： Hyperbolic reflective mirror
- Primary mirror material：PZ33（similar to Pyrex glass）
- Corrector：two-element air-spaced refractive lenses（including one ED glass）
- Minor axis of secondary mirror：65mm
- Image circle：44mm
- Field of view：6.9 degree
- Main tube material： High-end carbon fibre
- Main tube outer diameter：174mm
- Main tube length：394mm
- Net weight：3.2kg
- Gross weight：4.3kg（including protective cap, tube rings, handle and Losmandy-style dovetail plate）
- Resolution：0.89 arc second
- Focuser：2.5" with fine-adjustment
- Limiting visual magnitude：12.3
- Back-focus：55mm
Customer reviews
| Average Rating (1 Review): | |
27 January 2023 | Roy
This is a wonderful little Newtonian, looking very impressive in it's stunning red and black livery. It feels solid and well built, and the focuser controls are smooth and precise. It arrived in perfect collimation and has remained that way in the few months that I have been using it.
It really does cover a full frame sensor as advertised although. as you would expect, there is some light falloff at the corners but this is easily corrected with flat frames. I have been getting some excellent results with it using an ASI 6200 MC Pro full frame OSC and an NB1 tri-band filter. The fast F/2.8 ratio gathers light quickly and helps make the most of our limited UK clear skies.
There are a couple of small niggles. Although the focuser can be rotated to adjust camera orientation, it requires the loosening of three small screws located radially about the drawtube, which can be really fiddly in the dark and requires a small screwdriver. As the scope is small and light I found it easier to just rotate the entire tube assembly in the tube rings, and this leads me to the second niggle. Rather than use thumbwheels to tighten the rings there are allen keys. Being quite large they are easier to get to than the drawtube screws, and I think a good DIY mod would be to replace these with thumbscrews at some stage.
But these are minor niggles. Overall the scope is excellent and I can highly recommend it.
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