作為不少Lunt Solar System H-alpha 望遠鏡和濾鏡（包括雙濾LS100T 和LS152T）的長期用戶，我對Sky-Watcher 的HelioStar 76Ha 望遠鏡很感興趣，因為這是 該公司的第一次踏進H-alpha太陽觀察領域。有幸獲得一台 HelioStar試用，而且用 Lunt Solar Systems  LS100T 望遠鏡作對比。

HelioStar 中太陽表面絲狀物(filaments)與背景形成了非常高的反差對比。使用 TeleVue Panoptic 19mm、Ethos 13mm 和 DeLite 11mm 目鏡觀察，影像清晰迷人，類似經過處理的圖片。

與 LS100T  的頻寬(bandwidth) <0.7 Angstrom相比，HelioStar的頻寬為 <0.5 Angstrom，因此預計影像的對比度會更好，而這確實和觀察結果吻合。  LS100T 的絲狀物對比度明顯較低，我們需要在前面添加一個 LS100F，即用雙濾模式，才能獲得與 Heliostar 般的影像。當然，Lunt LS100T配合LS100F 雙濾的價格要高得多。

我們嘗試使用Binoviewer。可是，HelioStar 無法對焦，但 LS100T 卻沒有這問題。

HelioStar的設計使觀察更方便。例如，箱內的檔板為為觀察者提供遮蔭，調頻方法比Lunt Solar Systems 壓力調頻器更容易使用。

第二天，太陽表面爆發出一個直徑約 20-30 個地球直徑的巨大日珥。LS100T 中的影像比 HelioStar 的影像更光亮，解像度（resolution）也好得多，這也是 LS100T的較大口徑產生的預期結果。

第三天，我們使用 ZWO ASI290MM 單色相機拍攝太陽影片，可是HelioStar的調焦器質素一般，難以準確對焦，但拍攝出來的效果相當精彩。我們也嘗試加入 Barlow或Powermate 來提高放大倍率，但我們只能使用 Celestron 2x Barlow 來達到對焦。此外，較高倍數也導致曝光時間更長，視寧度開始明顯影響影像質素。

總而言之，Sky-Watcher HelioStar 望遠鏡合符其頻寬和口徑的表現，是性價比很高的產品，非常適合目視太陽圓盤(solar disk)和低倍攝影，尤其是長長的絲狀物。可是，對觀察日珥和高倍攝影則比LS100T差，調焦器質素也有很大進步空間。

作者：David Leong

星河科研社為SkyWatcher香港代理，此鏡eshop有售 https://eshop.astro.hk/hk/catalogs/products/22054624-94cb-4cd0-a0ab-9c534dcf8402

As a long-time user of numerous Lunt Solar System H-alpha telescopes and filters (including the LS100T and LS152T with an additional filter in double stack mode), I am intrigued by Sky-Watcher’s HelioStar 76Hα Telescope – the first venture of the company into the hydrogen-alpha solar territory.

This is a review of our testing of Lunt Solar System LS100T telescope and Sky-Watcher Heliostar 76Hα.

With an advertised bandwidth of <0.5 Angstrom, compared to <0.7 Angstrom for the LS100T and LS152T, I expected better contrast in the image, and this was indeed what I observed. The numerous twisting long filaments on the Sun in the HelioStar appeared with very high contrast against the brighter surface in the background. Using a TeleVue Panoptic 19mm, Ethos 13mm, and DeLite 11mm eyepiece, the image was crisp and mesmerizing, resembling a processed picture.

Setting up the LS100T for comparison, the disk appeared brighter with less contrast in the filaments, as expected with the slightly wider bandwidth. We needed to add an LS100F at the front to use the scope in double stack mode to achieve a similar contrasty image as the Sky-Watcher scope. Of course, the cost of the Lunt Solar System double stack setup is much higher.

We then tried to use a binoviewer with the telescopes. Unfortunately, focus could not be reached for the HelioStar but it poses no problem with LS100T.

Some special features of the new scope made the experience hassle-free and enjoyable. For example, the included card is great for providing shade for the viewer. The tuning mechanism is much easier to work with compared to the pressure tuning knob of Lunt Solar System telescopes. Therefore, for visual enjoyment of surface details, especially the long dark filaments, the Sky-Watcher scope is a clear winner.

The next day, a huge prominence about 20-30 Earth diameters across erupted from the surface of the Sun. This time, however, the image in the LS100T was much brighter and thus more stunning than in the HelioStar, which is expected due to the larger aperture of the Lunt scope. The resolution of the fine details of the prominence was also much better, which is to be expected because of the larger aperture of the Lunt telescope.

We also tried to take videos of the Sun using a ZWO ASI290MM monochrome camera. While adjusting the focusing knob of HelioStar, sometimes the focuser either didn’t move or suddenly slipped down, making it difficult to achieve accurate focus. We also tried to add a Barlow/Powermate to increase magnification, but we could only get the Celestron 2x Barlow to reach focus. The smaller aperture also resulted in longer exposure times, which isn’t ideal for the usually average to poor seeing conditions during day time at my shooting location.

To conclude, the Sky-Watcher HelioStar telescope performs as expected based on its specifications. It is great for visual observation of the solar disk. Its performance for observing prominences and photography aligns with our expectations given its aperture size and bandwidth, and it would benefit significantly from a higher quality focuser.