Coronado PST H-alpha 40 mm telescope

Coronado PST H-alpha 40 mm is a compact telescope designed exclusively for observing the Sun, namely its outer layer – the chromosphere. The lens diameter of this telescope is 40 mm and the focal length is 400 mm, however, even through such a small instrument you can successfully observe and photograph various chromospheric formations on the Sun – prominences, filaments, solar flares, spicules, sunspots.

Coronado PST H-alpha 40 mm chromospheric telescope.
Coronado PST H-alpha 40 mm chromospheric telescope.

The Coronado telescope is equipped with special filters that allow you to observe the Sun absolutely safely without additional protective solar filters, and is tuned to the wavelength of ionized hydrogen radiation of 656.28 nanometers (H-alpha), and the half-width of the telescope’s bandwidth is only 1 Angstrom (0.1 nanometer). It is precisely this narrow bandwidth that ensures the visibility of the solar chromosphere. The Sun, when observed through the Coronado telescope, appears red – this is the natural color of the glow of ionized hydrogen at a wavelength of 656.28 nanometers. The chromosphere of the Sun is very dynamic, prominences constantly change shape, and solar flares can occur in real time. In addition, the Sun is the only star whose disk and various atmospheric formations can be seen through a telescope.

Some technical details
My Coronado was purchased in the summer of 2011 (serial number 107815). The length of the telescope is 380 mm, width 54 mm, height 134 mm. Lens diameter 40 mm, blue coating. There is a thread inside the lens barrel with a diameter of 50.91 mm. A golden ERF (Energy Rejection Filter) filter is visible deep in the tube. The diameter of the golden tube is 50.1 mm. The eyepiece assembly has a mounting diameter of 31.84 mm (for 1.25″ accessories), a depth of approximately 30 mm. My version of the tube is quite old, although it is newer than even older “coronades” with an orange ERF coating of the front lens. In new telescopes, the color of the tube has changed slightly, the output visual back” under the eyepiece can now be unscrewed, and the image from the new telescopes seemed noticeably brighter to me, which is very good for both visual observations and astrophotography. I would also like to add that over 12 years of operation, no problems have arisen with the telescope. My telescope works great in both hot and cold weather.

Sun in H-alpha line, September 24, 2023, 10:22
Sun in H-alpha line, September 24, 2023, 10:22

The “heart” of a chromosphere telescope is the etalon – several glass plates separated by a thin air gap. By adjusting the distance between the plates, the telescope can be precisely tuned to the H-alpha radiation length.

Using the Coronado telescope is very simple, it has only two controls – focusing (a small knob on the back of the body) and setting the Fabry-Perot etalon (a rubberized ring at the base of the gold tube). The telescope also has a built-in sun finder – a glass window, in the center of which a small bright spot is visible when successfully aimed at the Sun.

Basic controls for the Coronado PST telescope
Basic controls for the Coronado PST telescope

1. Install the telescope on the mount.
2. Remove the lens cap and install the eyepiece.
3. Point the telescope at the Sun, looking at the finder window.
4. Look into the eyepiece and focus so that the image is sharp.
5. Rotate the etalon adjustment ring, achieving visibility of the chromospheric grid and prominences.

I recommend using eyepieces with a focal length between 25mm and 10mm. At shorter focal lengths, the solar disk will be too dim and low-contrast. When observing, it is advisable to cover your non-working eye with your palm, and cover your other eye from sunlight to reduce glare from the eyepiece, or even cover yourself with a black cloth.

You can see my photographs of the Sun, including through the Coronado PST H-alpha 40 mm chromospheric telescope, on my website AT LINK

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