Building a hydrogen alpha solar telescope

Creating a hydrogen alpha solar telescope has been a fascinating journey, one that required a deep dive into optics, patience, and a fair amount of problem-solving. I want to share the entire process with you, detailing every step I took to assemble a high-performance solar imaging system that delivers stunning images of our closest star. While I describe the build in full detail, I must emphasize that this project involves combining components that were never designed to work together. Neither Lunt nor Daystar endorse or recommend this approach, and there are no guarantees that what worked for me will work for you. That being said, let’s dive into the adventure of building a large hydrogen alpha solar telescope.

Building a hydrogen alpha solar telescope

I already owned a 100 mm double-stacked hydrogen alpha telescope from Lunt Solar Systems. It had served me well, delivering fantastic images. But I noticed that larger aperture telescopes were achieving levels of resolution and detail that I simply couldn't match with my 100 mm scope. Lunt's next step up, the 130 MT, was an incredible instrument, but at a price of around $12,000, it wasn’t the most efficient choice given that I already owned high-end apochromatic refractors, the TEC 140 and the TEC 160 FL. My TEC 160 FL, in particular, had proven its worth time and again for lunar, planetary, and deep-space imaging. Using a Lunt Herschel wedge, I had even taken a solar photo that won an Astronomy Picture of the Day (APOD) award. So, the question was: Could I convert my TEC 160 FL into a hydrogen alpha solar telescope?

Observing the Sun in hydrogen alpha requires a special filter known as an etalon. This optical device isolates the 656.28 nm wavelength of light, allowing us to see solar features like prominences, filaments, and granulation in remarkable detail. Etalons are expensive and challenging to manufacture, and they come in three main types: tilt-tuned, pressure-tuned, and solid etalons. My previous experience with solar telescopes had already introduced me to these types, but my specific needs and the constraints of my existing telescope meant that I had to be selective.

Expanding aperture in hydrogen alpha: My custom-built solar telescope journey

A tilt-tuned etalon over the objective wasn’t an option, it simply wasn’t available in the size I needed. Pressure-tuned etalons are built for specific telescope models, not for general use with whatever scope one happens to own. That left me with solid etalons, which are often integrated into systems like the Daystar Quark and Solar Spectrum models. While the Solar Spectrum line was my preferred choice, long wait times and limited availability forced me to go with the Daystar Quark Chromosphere model instead. The Quark is known for inconsistent performance, so I took my time searching for one that met my standards before making the purchase.

The Quark includes a single etalon, a blocking filter, and a built-in 4.3x telecentric amplifier, effectively transforming my f/7 refractor into an f/30 system. However, there was an important challenge to address: the Quark cannot safely handle unfiltered direct sunlight from objectives larger than 100 mm. This meant I needed an energy rejection filter (ERF) to be placed over the objective. The ERF reduces the intensity of incoming light, rejecting all wavelengths except for a narrow band around hydrogen alpha, while also eliminating excessive UV and IR radiation that could otherwise damage the optics or the Quark itself.

I measured my telescope’s aperture carefully and ordered an ERF from Baader Planetarium. This involved purchasing both the special glass disc and a custom cell to mount it securely onto my TEC 160 FL. After a long 90-day wait, the ERF finally arrived, and I was ready to move forward with the build.

My previous experience with the Lunt 100 MT had taught me that double-stacking an etalon significantly enhances contrast and detail. But how could I double-stack the Quark? Daystar doesn’t offer dedicated double-stack systems, instead, they sell premium etalons with a tighter bandpass at a steep cost. For example, a 0.5-angstrom Quantum etalon from Daystar runs around $22,000 and comes with a six- to eight-month delivery window. That wasn’t an option for me. Instead, I decided to take a different approach, one that other solar imagers had experimented with successfully: combining a Quark with a Lunt tilt-tuned etalon.

Assembling and tuning the custom hydrogen alpha telescope

To do this, I purchased a Lunt 40 mm hydrogen alpha telescope. This small but capable instrument is an excellent entry-level solar telescope, and I had previously reviewed it on my channel. I removed its tilt-tuned etalon and installed it into a special RAF adapter, allowing it to be integrated into my image train. I also removed the small internal ERF from the Lunt assembly to achieve a brighter image with lower gain.

With the hardware assembled, it was time for first light. My excitement quickly turned to frustration when I couldn't achieve focus on the Sun. After some troubleshooting, I discovered that I needed to add an 80 mm extender to my TEC 160’s focuser. Once in place, I was finally able to capture my first hydrogen alpha images with this custom setup.

To optimize performance, I added a Player One tilter to eliminate Newton’s rings, a common interference pattern that occurs in monochrome solar imaging. I also experimented with different cameras, including the IMX 432, IMX 174, and IMX 533 sensors. Given the f/30 focal ratio, I found that the IMX 174 provided the best results. Although the IMX 432 is a more expensive sensor, it delivered softer images compared to the 174, likely due to differences in frame rate and pixel structure.

Operating a large hydrogen alpha telescope presents unique challenges, particularly when it comes to tuning. The Lunt etalon was straightforward, I could simply turn its tilt-tuning knob and see immediate changes in the solar image. The Quark, however, was a different story. It has a ten-position tuning dial, and each adjustment requires a 10-minute warm-up period. Testing all ten positions means a theoretical minimum of 100 minutes of tuning time, not including imaging. When factoring in the added complexity of double-stacking with the Lunt etalon, the number of tuning permutations became overwhelming.

Additionally, solar seeing conditions fluctuate constantly, making it difficult to discern whether a change in image quality is due to tuning adjustments or momentary variations in atmospheric conditions. After many hours of trial and error, I identified the optimal combination of settings for my system.

The final result: A powerful and versatile hydrogen alpha telescope

The final result is a high-performance 160 mm hydrogen alpha telescope that delivers stunning detail and contrast. While I emphasize that this setup is neither recommended nor supported by the manufacturers, it has proven to be a rewarding and highly effective system for me. One of the advantages of my approach is that I retained full flexibility, my TEC 160 FL remains a superb deep-sky and lunar telescope, and I can still use it for white-light solar imaging with a Herschel wedge.

For those considering a similar project, there are a few key takeaways. First, you don’t necessarily need a premium apochromatic refractor like mine, an achromatic refractor from brands like Sky-Watcher or Explore Scientific would work just as well for hydrogen alpha imaging. The most important factor is having a robust dual-speed focuser capable of supporting a heavy image train without introducing tilt or flex. Many standard focusers are designed for lightweight eyepieces and diagonals, so ensure that yours can handle the added weight of an ERF, Quark, tilt etalon, tilter, and camera.

This project was a challenging but rewarding endeavor, and I hope you found my journey insightful. If you enjoyed this deep dive into building a custom hydrogen alpha telescope, please consider liking the video and subscribing to the channel. Your support helps tremendously, and I’m happy to answer any questions in the comments.

Stunning solar images captured with the custom hydrogen alpha telescope

How I created a Hydrogen Alpha Solar telescope