Custom-made Spectroheliograph
This particular spectroheliograph was designed by Christian Buil in France. He kept this particular design small and relatively simple for do-it-yourself amateur astronomers such as myself. I believe he also has spectroheliograph designs that are research-grade and costing tens of thousands of dollars. I opted for the dirt-cheap do-it-yourself and a-little-more-difficult route to build what is considered a beginner spectroheliograph. It is still a scientific instrument but, in order to keep the cost absurdly low, it really is a rather crude instrument.
The non-optical parts can be made at home with a 3D printer. If you don't have a 3D printer (I don't nor do I plan to purchase one anytime soon... although, I do admit that one would come in handy for model railroading), then you can have any 3D printing service do it for you and ship the printed parts to you. I had these non-optical hardware parts printed in France by a 3D print shop that is very familiar with making parts specifically for astronomy and especially this particular spectroheliograph. There are some specifications that must be met with no variation so I wanted to use a print service that had experience printing these specific parts. This place in France has experience printing the parts for this spectroheliograph so that is who I chose.
I am still waiting on the optical parts to arrive which are also coming from France. I probably won't see these parts until near the end of the summer. I believe these parts are made by various optical companies after you place your order so there is a bit of a lead time.
Unfortunately, much of the scientific world is coming to this. More and more things are being made in people's homes or in such small quantities that almost everything is custom ordered. This means that these products are only produced if someone puts the money up front. To compound this is the fact that only a very small percentage of scientific instruments are made in the US and this is not one of them. There are some exceptional products and instruments made in the US but, compared to the entire global market, the percentage is embarrassingly low. The US has fallen very far behind when it comes to science, electronics and anything technical likely due to the lack of manufacturing happening in the US in recent decades. Consequently, I often need to order parts from China and Europe (mostly England, France, Germany, Ukraine). Anyway, I'm still waiting on the optical parts to be made and shipped from France. (Actually, I'm still waiting on a book from France related to this project too!)
This instrument, when paired with one of my smaller telescopes, should provide more detailed images and data of the sun than I am able to capture with any of my other gear some of which is significantly more expensive than this spectroheliograph. That being said, this spectroheliograph is a vastly different type of instrument than any of my other solar filters.
Most solar instruments and filters specialize in capturing/viewing in a single wavelength or a relatively narrow band of wavelengths centered only on a single band. The narrower that band, the higher the price goes exponentially. Also, you are stuck at that wavelength with that particular filter or instrument. If you want to view or image a different wavelength, then you need to purchase a different filter/instrument.
Unlike most solar filters, this custom spectroheliograph is adjustable so you can move from one wavelength to another. You still only capture one wavelength at a time but you have a choice of which wavelength to capture in a range from ultraviolet light (the Calcium K wavelength which is mostly invisible to human eyes) up into the upper end of the visible red wavelength (the Hydrogen alpha wavelength). This is a huge plus which allows me to record data and images of the Calcium line, Helium line, Hydrogen beta line, Sodium line, and the Hydrogen alpha line. The price is nice too since it is a relatively simple homemade instrument.
The light path through the spectroheliograph is shown in the photo below. The light will be collected and focused using my Skywatcher 72mm ED refractor telescope. The odd-shaped spectroheliograph is inserted into the focuser of my telescope. At the front of the spectroheliograph is a very tiny slit measuring only 0.01mm x 4.5mm. This significantly cuts the amount of blinding light entering the instrument. The light passes through this tiny slit and then continues on to the other components in this instrument.
The light then goes through a collimator lens to refocus this beam of light that streamed through the slit. This refocused light then heads toward a holographic grating.
A diagram of a holographic grating is shown below. This holographic grating is what is adjustable allowing you to capture different wavelengths. The angle of the grating will determine which wavelength you see on your computer screen. The light is reflected, at an angle, off the grating up toward an objective lens mounted inside the spectroheliograph. This grating separates the white light (consisting of all colors in the color spectrum) into its component wavelengths. There are different types of gratings but holographic gratings manage to create less stray light and scatter than other types of gratings. These holographic gratings also provide closer lines with less structure error than other types of gratings. The downside is that this type of grating is quite fragile and vulnerable to damage if not handled carefully.
The light reflected off the holographic grating is directed at an angle toward the camera objective lens which will direct and focus the light onto the camera's sensor. The camera then sends the waveform to your computer. You will still see a range of waveform bands on the computer screen. You then must image only the narrow band you are interested in graphing/recording. You do this by selecting a Region of Interest (ROI) which includes only the single waveform band and then imaging only inside that ROI.
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