Welcome to our beginner's guide to aligning a finderscope with a telescope.
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What is a Finderscope?
A finderscope is like a mini telescope, or one half a pair of binoculars, that sits on top of your telescope.
Its job is to make it easier to find objects in the night sky than it would be if you were yo just use your telescope.
Finderscopes work by showing more of the night sky than your telescope does, but they work by centering on exactly the same piece of sky.
For example, imagine you want to point your telescope to look at Jupiter one evening. You'd find it almost impossible if you only looked through your telescope eyepiece.
The area of sky your telescope can see (its field of view) is so small that you could scan the sky near Jupiter for a long time and still not find it.
Do the same thing with a much dimmer deep sky object and you have almost zero hope of finding it!
Because finderscopes have much lower magnification than a telescope, they show a much wider area of sky. This makes it a lot easier to point it in the direction of the object you're after.
In the case of Jupiter, for example, it's easier to move your finderscope so that its crosshairs (or red dot) centre on the planet itself.
If your finderscope is aligned to your telescope, Jupiter will be in the eyepiece!
Types of Finderscope
There are two basic kinds of finderscope:
- Achromatic - These are like mini telescopes. They use lenses to magnify the view through them
- Reflex Sights - These do not magnify, but often have a 'red dot finder' or some other device to show where the centre of its field of view is
This is the most common type of finderscope which uses lenses to magnify the sky. You can find brighter objects and, when it is properly aligned, get them into the centre of your telescope's view.
Most achromatic finderscopes have cross hairs on the viewing lens. The point where they cross is the centre of the view.
These types of finderscope are identified by two numbers, such as 6 x 30 or 9 x 50.
The first number is the magnification and the second is its aperture. It shouldn't surprise you to learn that higher magnifications and larger apertures cost more money. They do have the advantage of letting you see fainter objects, though.
At a dark sky site, a 9x50 finderscope will make many Messier objects visible. This makes it a lot easier to position them in your telescope's eyepiece.
The disadvantage of lenses in a straight achromatic finderscope is they produce an image which is upside down. This can be a little disorienting at first, but you will quickly get used to it.
If you don't like trying to centre an object when the view is upside down, you can buy a right angle, correct image version. These have a prism inside which turns the image the right way up.
That prism has another benefit, which is to put a right-angled bend into the finder scope. Many backyard astronomers prefer this design because they are easier to use when your telescope is pointing overhead.
A reflex sight finderscope does not have lenses to magnify the view through it.
Instead, this is a 'straight through' view of the night sky. Reflex sights have either a red dot showing their centre or a pattern of fields of view circles on the reticle.
The most famous and best-selling example of these is the Telrad finder. This has circles engraved in the reticle which match the field of view through your eyepiece. Before you even look through your scope, you'll know what part of the sky you'll see - so long as Telrad and scope are aligned.
You may be wondering what the benefit of a non-magnifying finder is. Well, they have no inverted image, a huge field of view and, because of that, they are great for star hopping your way around the sky.
Many backyard astronomers enjoy both worlds. Don't be surprised if you see a fellow astronomer with a 9x50 achromatic and a Telrad. The Telrad makes star hopping easy, the 9x50 gives great detail for accurately centering the scope.
Other Features in Finderscopes
Above the basics described above, each type of finderscope can be bought with additional features to make it more useful.
Expect to find models at the top end of the price range which have illuminated reticles with varying brightness levels. Of course, these will use a small battery to operate them, but it will last a long time.
Best Finderscopes for Telescopes
Many new telescopes, especially cheaper models (below $300) come with finderscopes that will do a job but are far from great.
Below, you'll find our recommendations for the best finderscopes, with a quick idea as to price and quality.
Click the model to find out more details, including pictures and today's price on Amazon.com.
Model (click for price)
Achromatic - Angled
Achromatic - Straight
Achromatic - Straight
Achromatic - Angled
How to Align Your Finderscope in 7 Easy Steps
As you've read above, when the finderscope is aligned with your telescope it makes it very simple to center objects in your eyepiece.
Being able to align your finderscope is an essential job for a backyard astronomer. Thankfully, it is straightforward, even for a complete beginner.
To align your finderscope you'll need to work backwards. First, find an object that's easy to recognise with your telescope, then align your finderscope to it.
With help from Michael Bernardo's great video (which you can see in full at the bottom of this page), we'll walk you through seven simple steps to align your finderscope with your telescope.
Step 1 - Find Something to Point Your Scope At
As Michael says in this section of the video, set up your telescope outside in the daytime using an object down here on the ground.
Aligning at night makes it tough to see a suitable object to use. Using an object like the moon is no good as it keeps moving, so you'll never get your finderscope and telescope pointing at it at the same time.
Find an object a good distance away (quarter/half mile) that is easy to align to. Good choices are light posts, aerials and chimneys. Trees make a poor choice for two reasons: it's often hard to tell which branch you're focussed on and they move around a lot.
Alignment is easiest to do if you pick a distant, recognisable object that does not move.
Picked a suitable landmark? OK, then let's get into the alignment process.
Step 2 - Set Your Telescope up for Alignment
In this clip, Michael puts the lowest magnification eyepiece into the telescope's focuser.
This is the one with the highest focal length in millimetres. Ideally, we recommend using one that's at least 20mm to give you a nice wide field of view.
Step 3 - Centering Your Chosen Object
Now you're ready to go, it's time to find your chosen object and get it centred.
Point your telescope in the general direction of the object you're going to use for alignment (e.g. chimney, light post, etc).
Get your view as sharp as possible by focussing your telescope and then get the object as close to the centre of your view as you can. If you can't get it sharp, then you may need to choose an object which is further away (telescopes aren't designed to work well with nearby objects).
Keep in mind that the image you see may be inverted (mirror image) or upside down. It shouldn't matter, though, so long as your chosen object is at the centre of what you can see.
When you've done this, lock off your telescope so that it can move, because now it's time to adjust your finderscope.
Step 4 - Aligning Your Finderscope
You've reached the point where it's finally time to centre your finderscope on the same object you just centred in your telescope.
Look through your finderscope to see where the object is. Note that in most regular finderscopes, the view will be upside down. Again, this is perfectly normal, what's important is that the object you're using for alignment is properly centred.
Depending on the type of finderscope you have, there will likely be two or three adjuster screws you'll use centre an object in it.
In the clip below, Michael shares a great technique for tightening the adjusting screws for even pressure on the finderscope.
Step 5 - Finishing Alignment
With your object centered and the finderscope locked in place, it's time for a final check back through the main telescope.
(9 second clip)
If you look through the eyepiece and your chosen object is still centred, then congratulations! You have successfully aligned the finderscope with the telescope.
If there has been some movement, then just re-centre the object in your eyepiece. Make sure the telescope is firmly locked in place and then make adjustments to your finderscope to re-centre the object there to.
Step 6 - A Daylight Test Run
Before moving straight to night work, it is worth selecting another one or two objects in the daytime to make sure that the alignment is spot on. This also gives you a little practice in using the finderscope.
Select a different object to take a look at and move your telescope so that the object is centred in the finderscope. Lock the telescope in place and look through the eyepiece. If you've correctly followed all the steps above, you should see the same object perfectly in the middle of your eyepiece.
Step 7 - More Accurate Finderscope Alignment
It is possible to make even greater alignment accuracy by using higher magnification eyepieces.
In this last clip, Michael demonstrates a simple method of fine-tuning your finderscope alignment.
You don't have to go to this level of detail. But, if your 'thing' is faint, hard to find deep sky objects, then you'll appreciate the added accuracy this extra step brings.
The Complete Video Guide to Aligning Your Finderscope with Your Telescope
With that all complete, you are ready to use your scope at night. Make sure to avoid bumping your scope when moving it around. Slight knocks can move your finderscope out of alignment and may even make collimation necessary too.
You'll find now that whatever you centre in your finderscope is also perfectly centred in your telescope eyepiece too!
As promised at the start of this article, here's the video from Michael in full.
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Product images sourced from Amazon.com