Telescope Filters Which You Need! (Super Simple Guide)
So you have your brand new telescope, perhaps picked from our “super simplistic telescopes for beginners guide,” and you're ready to start observing. You look through the scope and suddenly realise “wow that moon is bright,” or “hmmm I mean this nebula is cool but it doesn’t look like the photos.” Ah yes, it’s an all too common first thought and was one which definitely caught me out!
Fortunately, there is a solution and it is one which you may already have the pieces for. Filters.
A lot of telescopes come with lens kits which may include eyepieces and filters. Take the lens kit I got with my first telescope, the “Celestron Eyepiece and Filter Accessory Kit.”
This kit was fantastic. It came with the telescope but more to the point it came with a whole range of filters which for the first year or so I did not even touch because I simply wasn’t aware of the benefits they provided.
So what makes filters so special? Well, there are a few types of filters. Some filters reduce glare, some reduce light pollution and some are designed to bring out features in planets which would otherwise be difficult to see such as the ice caps on Mars or storms on Venus! They are particularly useful for astrophotography, which if you are interested in getting into you can find a super simple beginners guide HERE.
The first type of filter I will discuss is a light pollution reduction filter (LPR). If you're like me, I did not have too much money to invest upfront into a hobby. I had already spent a large sum on tracking mounts etc. and looking back if I could only get one filter to begin with, it would be an LPR filter but that is only due to where I lived. Let me explain.
If you live in a remote location with very little light pollution you won’t need a light pollution filter and can spend your money elsewhere! Most of us however probably live near or in cities which really means we don’t have much of a choice when it comes to using a light pollution filter. The best option is to always drive away from the pollution as the truth is, while these filters do work to a degree, they will never provide mind-blowing results in the reduction of pollution you might expect.
With the transition to LED lights, these filters are becoming less effective as they are not designed to block out that wavelength. Therefore my recommendation to you is if you can get away from the pollution, save your money and do that instead! However, if you simply do not have a choice, a filter will give you at least some degree of reduction in light pollution and will improve your images but not by a whole lot.
Put simply a light pollution reducer filter removes certain wavelengths which radiate from common light sources (removes light pollution). While doing so, it allows other wavelengths not associated with light pollution to pass through such as the wavelengths emitted from a nebula for instance. This means that it will not dim the deep sky objects you want to observe, only the light pollution which you want to remove. The effect of this is you get a darker background while keeping the object being observed unchanged.
Take a look at the image below and notice the darker sky with a light pollution filter as well as the reduced glow from the artificial light!
As you can see it makes a reasonable difference in a polluted area! So what light pollution filters do I recommend you take a look at? The truth is there are so many and it really depends on whether you are using a telescope or DSLR etc. The filter which I recommend is the Optolong L-Pro. It comes in a 1.25 inch and can be purchased from Amazon in the link below (by clicking the images) or from optcorp.
Objects such as the moon can often be very bright causing eye-strain leading to headaches and furthermore, the glare can prevent you from seeing details. Think about it like this, wearing sunglasses reduces glare and allows you to see more clearly than you would without them. This is exactly what a neutral density filter does.
A neutral density filter evenly reduces light across the spectrum which reduces the intensity of light reaching your eyes and consequently providing you with much better viewing conditions! If you will be spending a large amount of time looking at the moon, it may be worth your time picking up a variable neutral density filter. A variable filter will allow you to adjust the reduction in light and therefore the brightness of what you are seeing. Below are my recommendations:
In the case of this filter, I was unable to find one for a telescope which was variable and neutral density, however, for the case of viewing the moon, the 1.25-inch filter one will work perfectly. Take a look around though perhaps at your local astronomy store, you may find a variable neutral density filter for your telescope eyepieces!
A similar sort of idea to a light pollution filter is a narrowband filter which blocks out all light emissions from wavelengths other than those in a very certain range. Oxygen III filters are the most common choice as they only allow 496 to 501nm lines to pass through the filter. This band of wavelengths allowed through are associated with the wavelength of light emitted from planetary nebulae. This effectively reduces any background light and only allows light from nebulae/planets to reach your eyes.
In the image of the lens kit I discussed at the beginning of the article you may have noticed a bunch of filters in different colour and that is the last type of filter I want to discuss. Colour filters are used to bring out detail in planets which may otherwise not be visible. For example, the great red spot on Jupiter, the polar caps on Mars, the belts on Saturn, dust storms on Mars and so many more features can all be more easily identified or even seen with the use of colour filters. Check out the chart I have included below showing you which colour filter works best for what detail you are trying to see!
As you can see there are HUGE amounts of options when it comes to what filter will allow you to see what feature. What I recommend is checking out a planetary filter kit like the ones I have listed below. If you are just getting started or don’t have a huge budget the smaller kit will serve you very well, in fact, that is all I used for many years once I started using filters! If you already have a few filters though or know this is a hobby you are happy to invest in, perhaps go for a larger kit with more options. Bear in mind though it is not required! You can get away with just a few filters when you're starting out.
That is it. That is the simple guide to getting your first set of filters! If you are looking to get into astrophotography go check out my super simple “Guide to beginning astrophotography,” or if you are looking to purchase your first telescope take a look at this “Guide to picking your first telescope for beginners (really simple and cuts out a lot of the guesswork!).” Now get out there and start observing with your new filters, wishing you all clear skies!