The first time you look through a powerful telescope, the sight of the night sky can be mind blowing. Telescope lenses can show you objects that were previously hidden from the naked eye. However, looking at the stars and planets through just a simple lens can get monotonous after a while. A magnified view is all very well, but what you see is nothing compared to the gorgeous pictures in astronomy books, websites, and magazines.
This is where telescope filters come in. By adding these to a telescope, you can filter out certain kinds of light and see what they’re blocking. Of course, it’s also important to choose the right kind of filter for your desired viewing experience.
What are Telescope Filters?
Telescope filters are coated filters that aspiring and professional astronomers can attach with their telescopes. With different hues and colors, the filter can improve the viewing experience in a number of ways as covered below.
These filters work by reflecting or blocking certain types of light. If this sounds contradictory to the claim of improving telescopic vision, then think about how you experience the beach or a sunny day in general. When someone goes into the bright sun, they can’t see everything clearly. All the rays get into your eyes, and you can’t even experience the details of your surroundings. This is partly why we wear sunglasses or shade our eyes in such situations; by blocking out some of the light, we can better view the colors of a bird outside, enjoy the movement of the waves, and more.
Why Do We Need Telescope Filters?
We need telescope filters in the same way as we need sunglasses or some other type of shade; to control the quantity and type of light that our eyes can perceive. Plus, blocking some wavelengths will help us see the rest of the transmitted light better than before. This means a better, sharper contrast as well. Celestial bodies emit or reflect different wavelengths of light. With the right filters, we can fine-tune our telescope according to what we want to see in the sky.
Do Beginners Need Telescope Filters?
If you’ve just started viewing the sky with a telescope, it’s easy to think that an unfiltered view is exciting enough. A telescope will help you view the brightest stars and the moon with much more clarity and details than with the naked eye.
However, even a complete telescope novice will soon crave more contrast, light, and sharpness while viewing celestial objects. If you’re still in the beginner phase, there’s no reason to avoid using filters. Even those who want a guide to choosing the right telescope for your child may also look for filters that can fit those smaller models.
In fact, using telescope filters will probably increase a beginner’s interest and motivation in stargazing. The filters lead to new experiences even when you’re looking at the same thing over and over again. They allow us to see more details and even bring new objects into view.
Types of Telescope Filters
So, what are the types of telescope filters one should consider for their stargazing? Let’s check out some of the most common and useful ones below:
These filters allow a person to view the sun through a telescope. There are some different variations within this category too, but the best ones are usually full-aperture filters.
Full-aperture filters are the safest for viewing the sun. This is because they consist of flexible glass or film, which covers the telescope end and reduces the effect of the ultraviolet (UV) rays, light, and heat from the sun. Even with these filters, you are still looking at the sun. Be careful not to look directly at it with the naked eye as this can cause permanent damage.
If you would like to see some more details of the sun, try the solar H-alpha (hydrogen-alpha) filter.
There is also the option of white light solar filters, which allow the viewer to view sunspots and also see a solar eclipse with some detail. However, H-alpha filters might be a better option since they only transmit one wavelength of light. This is a deep red color that comes from hydrogen atoms. Here are some other reasons to use this filter for sun viewing:
- The sun’s chromosphere will be visible; this is a layer that can go up to 20,000 degrees Celsius
- It can also help the viewer to see some bright nebulae
- It has a wavelength measuring around 656 nanometers, which means that it blocks out the dangerous types of light coming from the sun
The main purpose of a lunar filter is to reduce the brightness across the entire visible spectrum and come in different strengths ranging from low to high. As a result, it should be easier to see the details on the moon through a telescope here on Earth.
There are two main kinds of lunar filter:
- Neutral Density Filters: These can darken a certain area of the surface of the moon. This way, the viewer can view different parts in turn and appreciate their detail more
- Variable Moon Filters: These allow the viewer to control the level of light passing through it through polarization adjustments. It’s the right choice for anyone who wants to view the moon in varying phases. You can decrease the level of light during the gibbous phase and increase it during the crescent phase.
There are some green-colored linear filters available too that can help reduce glare from the moon. While the moon doesn’t shine like the sun, even its reflected light can become uncomfortable when viewed through a telescope without filters for elong durations of time.
Color or Planetary Filters
These are the filters you use when you want to view planets and enjoy their unique details. Planetary filters usually come in single colors–violet, blue, and so on. These will filter out all other colors in your view–leaving only the color of whatever filter you’re using. As a result, the images you see form the telescope will have enhanced details and better contrast.
Since planets have different main colors, we will have to use the filters accordingly. Here are some filters that can help you view your favorite planets with a lot more clarity:
A #25 Red filters will be useful here; it will enhance the disk of the planet. You can use this filter to view Mercury at the best time, which is at twilight, right after the sun sets.
A #47 Violet filter helps in reducing the high level of brightness that can otherwise spoil your view.
You may have to use more than one filter here. #21 Orange is useful here for glare reduction, allowing you to view the surface in more detail. #15 Deep Yellow is also a good choice here, as it will help you detect the polar caps.
This is a planet with a lot of interesting cloud bands and colorful hurricanes. The #58, #80A, and #21 filters can help bring out these details.
#15 Deep Yellow is great for bringing out the details of this beautiful planet. It can also help to sharpen any astrophotography images you might want to take.
Similar filters are applicable for viewing other planets. You may also need to use light pollution filters (discussed ahead) depending on your viewing location.
Light Pollution Filters
Light pollution consists of artificial light which might be an obstacle to clear night sky viewing. Houses, streetlights, and shop lights can all get in the way of viewing the stars and planets even with a telescope.
This is why a light pollution filter is useful–it reduces the effect of artificial light and makes the sky darker. As a result, celestial bodies will be more visible.
These filters will admittedly make nebulae less bright through your telescope. However, they will also boost the contrast, which means that more details are apparent this way.
Filters are ideal for deep-sky viewing, like when we want to see nebulae in the sky. It will work by only allowing emissions like Hydrogen Beta and Oxygen III. With the effect, the sky view will darken but bring the celestial object up for a better viewing experience. These filters are versatile and work even where there’s medium magnification and a certain level of air pollution.
These serve to reduce glare and darken the sky at night. You can also use them on top of each other to darken the view more if required.
UV/IR Cut Filters
These help in blocking UV and infrared wavelengths so that a monochrome camera can capture celestial bodies’ luminance. It will also cut off wavelengths that you don’t need in color cameras–overall, they’re more used in taking photographs of the night sky instead of just viewing it through a telescope.
Making Your Own Solar Filter
After checking out the top 20 telescopes for astronomy, you may decide on a single perfect choice. If you can’t find the right size of solar filter or don’t want to buy it right away, there’s a way to make a DIY version.
To start with, you will need the following equipment:
- Solar mylar film
- Can (should be able to fit snugly into your telescope)
- Can opener
- Remove the can’s label and thoroughly clean it
- Cut off both ends of the can
- Mix the epoxy
- Dip an end of the can in the epoxy mix
- Put the solar film on a table (dark side up)
- Press the epoxy side of the can on the film
- Wait for the epoxy to set (around 5 minutes)
- Ensure that no light can enter around the film
- Cut off the excess film and fit the can into your telescope
How to Use and Stack Filters
Before attaching a filter on a telescope, take out its eyepiece. Then, thread your filter inside so that it fits the eyepiece barrel at the bottom. Replace the eyepiece and you’re done!
There’s also the option of stacking your filters to get the desired results. For instance, you may put in a light yellow filter and stack it using a neutral density filter for glare reduction and enhanced contrast. Not every filter will be stackable, though, so make sure to ask the vendor about this when making the purchase.
Viewing the sky through a telescope can be an exciting hobby that is educational and fun at the same time. It’s also one of the best hobbies to consider if you love to travel–different places around the world will give you new views each time. Whether you’re just looking to experience something new or have an active interest in astronomy, investing in telescope filters is a must for stargazing. Think about what you want to view first and then look for the right filter accordingly. If you don’t have a telescope yet or are looking for a new telescope, read our Guide to Picking a Telescope so that you can purchase the most suitable telescope for you before investing on filters.