How To Make A Hydrogen-Alpha Filter

A Simple Guide On How To Make A Hydrogen-Alpha Filter

Being interested in the sun is nothing new in astrophotography. But the sun’s bright light outshines everything; making it impossible to capture a photo. 

That’s why an h-alpha filter is necessary to capture a sun’s photograph. It blocks the massive white light; letting you see the sun for itself. 

However, the filters are extremely expensive. That’s why many astrophotographers often wonder- how to make a hydrogen alpha filter? 

Assembling a hydrogen-alpha filter is a cheaper option than buying a commercial one. The etalon filter captures the right wavelength. You’ll also need a blocking filter to block other wavelengths in the telescope. The sun also emits harmful ray which is blocked by using an energy rejection filter. 

However, there’s a lot more to discuss, a lot more factors to consider. Stay with us if you want to know more about hydrogen-alpha filter astrophotography.

How Does A H-Alpha Filter Work? 

Before we head into the main discussion, let’s talk about how they work. Because knowing them will make it easier to understand in case if you’re new. 

There are mainly two types of hydrogen-alpha filters. The first one is about observing the sun in the day sky. 

The other one is about nebulae photography in the night sky. For nebulae photography, a hydrogen-alpha filter enhances nebular contrast. The latter can’t be used to look at the sun. It’s extremely dangerous for your eyes. 

There is a special hydrogen-alpha filter for telescopes to capture the sun’s photosphere. These filters work on the right wavelength which negates the massive white light.

What Is A Hydrogen-Alpha Wavelength

Hydrogen like other atoms emits light at different wavelengths. One such emission has a wavelength of 656.3 nanometers. This is a reddish-orange light. 

This only happens when an electron falls to the first excited state. In a hydrogen atom, the 2nd stage is normal. This falling creates this reddish-orange light which is then used as a filter. 

The telescopes that use this feature are called h-alpha filter telescopes

This filtering effect help passes the light through a narrow band. It blocks the white light and as a result, you can see the sun for itself. And that’s what makes hydrogen-alpha filter for solar viewing so popular.

What Are The Main Components Of H-Alpha Filter? 

So far we’ve only talked about how the H-alpha filter works. The process may have sounded super simple but it depends on several components. 

The h-alpha filters used in H-alpha photography have 3 different parts. These are called the etalon, blocking filter, and mounting cell. All 3 of them consist of a set and work together. 

Other than that, there’s also an energy rejection filter which is necessary for safety.

Can You Really Make A H-Alpha Filter By Yourself? 

Every telescope has different purposes. This difference is due to telescopes having different components. These components are usually super complex and very precise. 

For example, birdwatching binoculars and astronomy ones are completely different. The lenses and the focal lengths aren’t the same and that’s what set them apart. 

Commercial H-alpha filters are super expensive. They can cost around $2000 to $6000. The good ones usually cost around $3500 to $5000. 

Since they’re priced that much, it’s not uncommon to wonder about making them. Luckily, you can buy cheap parts online and assemble them yourself

The Etalon Filter

You can call this the heart of the H-alpha filter. This etalon filter has two mounted plates that are highly reflective. This filter catches the lights with the right wavelength. 

The other ones get filtered instantly and do not enter. This allows you to capture light waves around 656.3 nanometers. This is the wavelength we’re looking forward to. 

It’ll also help you in building a sun spotter telescope by yourself.  

But this isn’t the end of it. There will be some light waves that’ll enter beside the right one. That’s why we’ll need a 2nd component; the blocking filter. 

The Blocking Filter

The blocking filter is a diagonal lens. This is used to block every other light that enters the etalon. This lens only allows the right wavelength of 656.3 nm to pass through. 

This blocking filter comes in different sizes. The smaller sizes suit the telescopes with shorter focal lengths. 

So, if your telescope is bigger, you’ll require a bigger blocking filter. 

Speaking of the diagonal lenses, we picked the best one for you- SVBONY SV188P Dielectric Mirror Star Diagonal

The Energy Rejection Filter

Like the etalon filter, this is also another super important part of the assembly. Without it, you’ll get your eyes damaged. Because after all, looking at the sun isn’t a safe task. 

This is also called the ERF filter for short. They come in different apertures. The variety of apertures ranges from 80mm to 150mm. 

Sadly, there is a downside. The filters with a higher aperture cost more. But you can always find some ERF filters for super cheap on sites like eBay. 


Question: Is H-alpha visible?

Answer: Hydrogen alpha is a spectral line in the series of Balmer. It’s totally visible and has a deep reddish hue. This is also super bright and the most visible in the spectrum. 

Question: What is a hydrogen beta filter?

Answer: Unlike H-alpha, the H-beta filter has a lower wavelength of 486nm. Using this, you can clearly see the H-beta emission effortlessly. This occurs when an atom falls to the 2nd stage from the 3rd stage.  

Question: How do you observe the chromosphere?

Answer: The chromosphere is the 2nd layer of the sun. To observe the chromosphere, you’ll need powerful telescopes that are made specially. On top of that, you can only see them during a solar eclipse. 

Final Words

These were everything that we could deliver on how to make a hydrogen alpha filter. Hopefully, this discussion was able to shed some light on your confusion. 

Also, don’t forget to double-check the focal length of your telescope. Because all the components will have to adjust your telescope. 

Finally, have a nice day!

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