What is Bard membrane? Should I choose 3.8 film or 5.0 film when taking pictures?

The bud membrane is actually a solar filter. It is a metal-coated resin film that can be used for visual inspection and photography. It's very thin and the optical quality is very good. Bard film is currently available in two densities, 5.0 (visual) and 3.8 (photographic). Astronomical telescopes require Gabbard membranes or other filtering devices to observe the Sun.

Must be placed at the objective lens end. Maybe the intense heat of the telescope's focus would burn it out. Why not measure the thickness of the objective lens before buying it? Or you can make one yourself, use cardboard to make a sleeve that can cover your objective lens, and then dig a hole in it, 50mm, and then stick the film you bought on it, stick it firmly, and don’t break it

< p>Not many people know about astronomical telescopes for popular science, let alone smaller prominences. After buying a telescope, friends who like astronomy usually look at celestial objects such as large planets, the moon, and nebulae at night, and look at the scenery during the day, leaving only the sun to observe celestial objects. It is emphasized that you should never look directly at the sun with a telescope. Because the objective lens collects hundreds of times the light and heat of the sun, if observed directly, the concentrated strong sunlight will reach the human eye instantly, directly causing the retina to burn through, causing permanent blindness.

So what should friends who like to observe and photograph the sun do? If you only photograph astronomical phenomena such as sunspots and the transit of Venus, you only need to add a layer of AstroSolar film in front of the telescope, which is a metal-coated resin film that feels like a plastic film.

There are two advantages to using Bard film to observe the sun, one is safe, and the other is cheap (tens to hundreds). However, the Bader membrane has its limitations, that is, it cannot observe other solar activities such as the corona and prominences, so the prominence mirror was born.

The Corridor is a violent event in the sun's chromosphere, like a flame extending from the edge of the sun. Static prominences can last for several months at high solar latitudes and are typically as high as 40,000 kilometers and 200,000 kilometers long. Active prominences are short-lived and can change shape in just a few minutes, which is quite spectacular. But the brightness of solar prominences is much lower than the brightness of the solar photosphere, so the brightness of solar prominences is usually submerged in the strong light emitted by the solar photosphere. Before the invention of the prominence mirror, astronomers could only photograph and observe prominences through total solar eclipses.

Prominence mirrors are good, but the manufacturing process of this solar H-α narrow-band filter mirror is very demanding. There are very few manufacturers in the world that have mastered the production process of core components of prominence filters, and there is not even one in China ( may be too small). Therefore, the current price of prominence mirrors is not cheap. The 50mm H-α narrowband filter dual filter set costs more than 7,000 yuan, which is tens of thousands. So, I want one.