When you’ve looked at the gibbous or full moon through your telescope, you’ll have thought 'that’s really bright'.
That glaring brightness is why you’ll should have the best moon filter for your telescope!
Not only will having a moon filter make your lunar viewing experience so much more enjoyable, but it will also become more rewarding as you see more detail than you ever have before!
In the rest of this article, we're going to take a look at what moon filters are, why you should have one, and some of the best ones on the market right now.
What is a Moon Filter?
There are all kinds of filters to insert into your telescope eyepiece. These bring out details in objects like planets and nebulae that you just can’t see with the naked eye.
A moon filter is similar, but it acts more like a pair of sunglasses.
With a moon filter in place, the harsh brightness of the moon is dimmed and you are presented with much better contrast. This means you can see smaller surface details more clearly, so you can get the best use out of your lunar map.
(If you want to look at deep space objects, then you need this filter info instead).
How to Use a Moon Filter on a Telescope
You may be a little anxious about whether your telescope will take a filter for the moon if you’ve never used one before.
Well, you should not fear!
Pretty much all telescope eyepieces come threaded at the bottom. Your moon filter (or any other kind of filter, for that matter) screws onto that. All you need to know is whether you have a 2” or 1.25” eyepiece and make sure you get a filter that fits!
When you have your filter in hand, screw it onto the thread on your eyepiece, pop the eyepiece into your scope as normal and you are good to go!
Types of Moon Filter
There are only two types of filter that you need to be aware of:
1) Fixed Brightness Moon Filter
This type lets only a certain amount of light through, measured as a percentage.
For example, a 13% filter only lets through 13% of the light which hits the lens or mirror of your telescope; a 25% filter will let through 25% of the light.
Generally speaking, if you have a smaller telescope you can let more light in - since it’s not collecting much to start with. A 25% filter is fine up to around a 4” or 5” aperture. Anything bigger than that and you should be choosing a 13% filter.
2) Variable Moon Filter
As its name suggests, this kind of filter lets you choose how much light to let through.
It consists two pieces of polarised glass which change how much light comes through, when turned relative to each other.
These are particularly useful if you're a keen moon observer. You can let more light in when the moon is at a crescent stage and reduce the light coming through when its gibbous.
Moon Filter Review
Now you know pretty much all there os to know about moon filters, it’s time to discover the best moon filter for you.
Below we’ve reviewed five of the best sellers on Amazon, click on the picture or the button to find out the latest price. You’ll be pleasantly surprised that this is one of the least expensive pieces of astronomical equipment that you can buy!
This Orion filter is perfect for you if you have a smaller telescope.
Telescopes with an aperture below 4" don't let in as much light as the larger scopes, which means you don't need to filter as much of it out.
You may also find that the 25% transmission works well for waxing and waning crescent phases - even in a bigger scope - because the smaller moon is not as bright as the gibbous or full moon.
This 13% filter is one of the most popular fixed-brightness filters on Amazon.
As noted earlier, this is the kind that you need once you get into the realms of larger telescope apertures - think 5" and above.
Its neutral color is designed to not alter the actual color of the lunar surface through your scope, so all that happens is the light is 'dimmed', rather than changed.
The mood of the reviews is overwhelmingly positive: you won't be putting a foot wrong with this filter.
This Meade lunar filter has the same specification as the Orion immediately above.
These filters should fit with any 1.25" eyepiece, but I find it 'safer' to stick with the same brand. That way, you can be certain that you won't have issues with the threads or fit, etc.
There's not much to add to this Meade moon filter
For the sake of completeness, I have included this moon filter for Celestron lenses. But, seriously: DO NOT BUY THIS FILTER!
The write-up is poor and there are just too many reviewers saying they wish they'd spent a few bucks more on a better filter.
The common complaints are cheap plastic, poor quality threads and a green tinge to the filter itself!
I've left the links live, but if I were you - I would stay well away from this stinker!
I'm pleased to move onto better things, and this Orion model is a serious variable filter; the only one in this review of moon lenses.
As mentioned above, this kind of polarizing filter is only for serious moon gazers!
It has two rings of polarized glass, which can be turned to change the amount of lunar light they let through. The scale of transmission is from a full-moon-dimming 1%, all the way up to a 'day-2 crescent' 40%.
Although showing the 1.25" model here, it is also available in 2" size (just click the button below to find it) and both sizes come with their own storage case.
The most common FAQ about these lenses is whether they can be adjusted when in place. The answer: yes, you can adjust the filter whilst it's attached to your eyepiece, but you may need to have the filter above the eyepiece.
If you want to treat yourself and never again have to worry about the brightness of the moon, then this is definitely the filter for you!
Hopefully you've selected the perfect lunar filter for both your telescope and the level of passion you have for lunar astronomy.
If there's anything you're left wondering about, then check out this short video from Orion Telescopes and Binoculars, which should clear up any lingering questions.
Product images sourced from Amazon.com