A finder scope is used to help a new, or experienced astronomer achieve a generalized alignment with what they’re are wanting to get a better look at.
Most finder scopes have crosshairs inside the scope that will help you line things you’re trying to see up better. It is a lot easier to get your first general alignment using a finder scope than it is trying to guess where the object is while using the telescope itself to look around.
As anyone who has ever used binoculars or a zoom lens on a camera can tell you, it’s easier to find something if you have a rough idea of where to look for it to begin with. That’s what the finder scope does for you. It helps you get a general idea of where to find what you’re looking for, before you really start to hone in on it.
Optical tube finder scopes
These are simply a type of refractor telescope. It’s like having a mini telescope, or low power binoculars, attached to your telescope. There are several different types to choose. Some come with illuminated crosshairs, some have straight through (Tube style) viewing, and others have an eyepiece that is equipped with 45 degree viewing. Most telescope kits come with an optical tube finder scope.
Reflex sight finder scopes
Sometimes called red dot finders due to the red dot or circle that they use for alignment, and they usually do not have any magnification at all. However, they are easy to align and to use. The idea is simple. A red cross hair or bull’s eye is projected against a small glass or plastic window. You simply look directly at the sky trought this little window which displays the cross hair. Ajusting the projection simply involves twisting screws or knobs. The process can be done in a matter of seconds. This is by far one of the easiest finder scope to use.
Illuminated Finder Scopes
This type of finderscope is essentially a combination of the optical tube finder scope and the relexf sight finder scope. We’ve talked in other sections about the what a hindrance light pollution can be, if you have a beautifully dark sky to look at, with no light pollution to consider, you may enjoy using, and want to consider an illuminated finder scope.
However, if light pollution is a concern, then an illuminated finder scope will likely cause you to see annoying black lines.
Finder Scope Magnification
Magnifications of finder scopes can vary. Reflex sights finder scope usually don’t have a magnification. There’s two numbers found on optical tube finder scopes. One represents the magnification, the other represents the aperature. For example, 8×50 means 8 times the magnification with a 50 mm aperature. This is the minimum magnification you should look for. Don’t assume that stronger is better however. If the finderscope is too powerful, it will be much more dificult to use because you can easily “get lost” in the sky when looking through it.
Aligning your finder scope
After attaching your finder scope to your telescope, you will need to align it. This can most easily be done by picking something on the ground to line up with. If your scope is one of the ones that has some magnification to it, then you will want to set it on the lowest possible setting.
Then pick a distant point to center on, like a far away light or electrical pole. You will want to center your telescope eyepiece with the top of whatever you are looking at and then center the crosshairs of your finder scope on that same point. It is very important that you do not move the telescope at all until after you have done this. However, once this step is complete, you will want to test out your alignment.
Center your crosshairs on a few other far off objects. Center on them with your finder scope, if it is properly aligned, you should be able to see the same object in the main telescope. This will get you a rough alignment. To finish the alignment follow the exact same steps at night, using a star as your focal point.
Alternative to finder scope
An option that is getting more and more popularity is to use a green laser pointer mounted on a bracket. Traditionally, the green laser pointer is a hand held tool used to point out objects and constellaitons in the night sky. It is actually quite impressive, and efficient. A thin green streak of light is generated from the hand held stick. The green light travels about 3000 meters so this is one long beem of light! It is the perfect teaching tool since it makes it easy to point out objects. In recent years, bracket mounted green laser pointer kits became available and many users completly drop the traditional finder scopes and opt for the laser kits.