Introducing the innovative primary mirror coatings of the Soleye 300, custom-made for H-alpha and Calcium-K

We currently offer three different primary mirrors for the Soleye 300. One is uncoated, and the others are coated using a unique and innovative method. These three mirrors cover the most popular methods of solar photography: continuum, H-alpha, and calcium-K.

What are these, and how do the mirrors achieve the results you can see in our Gallery? You can find out all about it in this blog post.

Focusing the photons is only a part of the job in the solar telescope. While doing that, the massive amount of incoming energy must be mitigated, or it will overheat the structure in a blink. 

Telescopes and cameras have an imaging optic, the front lens. Additional lenses fine-tune and correct the image, but the source of the image is a singular object. In the case of solar telescopes, the primary mirror plays this role.

If you're reading this, you're probably someone who enjoys exploring natural phenomena, is intrigued by science and likes to test things for yourself. As a kid, you've probably burned a piece of paper by focusing sunlight with a magnifier glass (if you have not, it's never too late to try this interesting experiment). 

When focused, the Sun's image burns! The magnifier acts as an imaging optic. When turned towards and centred on the Sun, the image of the star will appear on the surface over the other side of the glass - and if that surface is flammable, the concentrated image will light it up, because you focus all the photons; thus you concentrate the heat as well.

The Herschel prism is one solution for eliminating this excess heat from a telescope pointed at the Sun.

This prism catches and disperses most of the incoming light (96%) and mirrors the rest. This solves the overheating issue, and 4% is more than enough to provide a clear image.  

Telescopes equipped with mirrors utilise a similar effect. Parabolic mirrors have the same imaging qualities as lenses. 

When a camera lens turns towards the light source, it will provide a focusing effect, gathering the incoming light energy into a smaller spot. In contrast, our uncoated mirrors reflect and focus 4% of the incoming light.

Our mirror uses 10 - 1 nm bandwidth filters, enabling us to observe the visible surface, the photosphere ('in continuum').

4% is still plenty of light, offering good image quality. We can take a good look at the ebb and flow of granulations or the sunspot formations.

But there are many other exciting things happening on and over the Sun's surface. You just need the appropriate tools to take a good look at them.

Where the coatings come into play

Phenomena are going on outside the photosphere: stuff sometimes leaves the surface of the Sun. This area is the chromosphere, where the beautiful and exhilarating events of the Sun's magnetic activity play out.

To take a look at those events, more than just catching 4% of the light is required. 

The coatings lower the reflection quality of the mirror in the bandwidths that we can ignore and raise it where they are important for us.

Typically, solar photographers are interested in two distinct bandwidths of light: at 656 nm (called Hydrogen-alpha) and 393 and 396 nanometers (called Calcium-K and Calcium-H). One is deep-deep red (almost infrared bandwidth) the other is very-very blue (almost ultraviolet).

So, we designed a specific mirror coating for both of these bandwidths.

The Calcium mirror's reflection is enhanced by 50% in the appropriate bandwidth, which is right on the edge of the solar spectrum, making our job a little bit easier.

H-alpha is trickier, as it is right in the middle of the spectrum and carries a lot of energy. 

In any case, at least 90% of that energy must be reflected, and the rest is still a high amount, so for H-alpha photography, an extra filter is needed to keep the telescope's temperature under the overheating threshold.

Our coatings are done with a method called 'interference' - these are not metallic coatings like gold or copper. (The technique is still in the process of being registered as intellectual property, so we can't delve into details just yet).

This method can be considered high-end and innovative because steaming surfaces this size (the primary mirror has a radius of 30 cm) is something entirely new. There has yet to be an effective method for this, but we developed one.

Now, we will open the Soleye gallery and bring some examples of what we can observe with them.

'Soleye Red' - coated primary for H-alpha

H-alpha sunspot & prominence, telescope: SOLEYE 300 + H-alpha upgrade kit camera: ZWO ASI 174 MM filter: Daystar Quark Chromosphere

The brightest area in this image is the edge of the Sun. The right side of the image is inverted to make the 3D phenomena more pronounced, formulated, easier to understand.

On the left side, we can see a protuberance, a slower one behind and a more active, quicker one closer to us. 

On the right side we can observe the shapes of magnetic force bursting through the surface, thanks to a bipolar sunspot group. The outbursts flow from one bright area towards the other: they exit from one spot and submerge in the other. 

This phenomenon is visible because ionised particles are floating in the magnetic currents: ionised Hydrogen emits light in its frequency, which we call, of course, Hydrogen-alpha.

 In this image, on the right side, you can observe these particles from above. On the left side, you can observe them from the side as protuberances as you look at the Sun's surface area turning towards you, just entering your field of vision.

The key is the extremely high resolution we can achieve with the Soleye 300, making these phenomena so beautifully observable.

'Soleye Violet' - coated primary for G-band, Ca-K and WL

For reference, let's take a look at an image done in continuum first.

AR3034 equatorial sunspot: telescope: SOLEYE 300 camera: ZWO ASI 174 MM filter: Baader solar continuum

This is the plasma ocean, the surface of the Sun. The light parts are 500 km high, separated by dark valleys that are 500 km deep. One granulation (the fragments) is roughly the size of Australia.

Now, let's take a look at something like this in Calcium-K:

Solar Faculae and reverse granule in Ca-K around AR3641; telescope: SOLEYE 300 Violet Mirror, camera: ZWO ASI 174 MM filter: Soleye Reverse Granule 0,37 nm Ca-K filter

 Looks similar, but the valleys are now lit up.

 Under the surface, huge magnetic fields race around as the magnetism of the massive material changes due to the star's constant spinning. The ionised plasma on the surface provides a dampening cover, but that surface, as you can see, is fragmented. Magnetic energy bursts out in those fractures between two neighbouring cells. 

You can observe the Chromosphere network of these magnetic energy bursts. This provides insight into the fact that there are larger convection zones below the surface, and that is where the magnetic forces launch up from, looking for small wedges between the granulations where they can burst out and light up the Sun's surface. 

One reason why our telescope revolutionises solar photography is that we can offer these coatings for the relatively huge primary mirror. This enables the Soleye 300 to utilise much light, so the images can be done in high resolutions, offering many details.

Does this sound interesting?

Send us a message and we can hop in a call to discuss anything you'd like to know about the Soleye project!