The Finder Scope
By Shawn Grant
A finder scope is a little telescope that mounts on your main telescope. It is used to help find objects in the sky. It is usually 2 inches in diameter and has a power of 8. This will allow you to gather some light and magnify a little bit. It will let you see fainter guide stars and some brighter deep sky objects. This will greatly aid in finding deep sky treasures.
A common question is which is better the Telrad or finder scope. Neither is better then the other but they do have some advantages and disadvantages in each. One of the advantages with the finder is the fore mentioned aperture and magnification for finding more guide stars for homing in on your object. The main disadvantage with a finder is the magnification and the flipped or mirror image can disorient the user and make finding object frustrating. If you were just going to have one or the other I will probably recommend the Telrad. For more advanced users the use of the Telrad in combination with the finder scope. This will lot you have the best of both worlds. You can take the advantages of the Telrad and finder scope.
How do I find objects with a finder scope? First you need to determine the orientation. Typically a straight through will have an inverted image just like a newtonian telescope. Some finder scopes have a right angle prism. This will make the finder more comfortable to use, but it will make a dreadful mirror image view. Next thing to do is to make an overlay of your finder for your star charts. You will need to know the field of view of the finder. Most of them are five degrees. You can find out for sure with the literature the manufacture may send. You will also want to use charts that show stars down to 8th or 9th magnitude. Let’s find something simple now. We will look for M13. Center your finder on eta Hercules. If you look on the southern end of the finder you should see a little fuzz ball. If you can’t move a tad bit to the south and you should see it. That fuzz ball is M13. Just center the fuzz ball and look in the eyepiece you will see a glorious view. Let’s move onto something a little more difficult. The object will be M33. Center the finder scope on Alpha Triangulum. Move the finder about 4 degrees to the west. At a dark site you should see M33 in the finder but if you are in a suburban area you may have a little difficulty seeing M33 but it is there just look in the eyepiece.
The finder scope field of view I used is five degrees. Your finder scope maybe a different field of view so you will have to adjust for this. One thing to remember practice is the key to success. Nothing can replace actually going out to use your scope on the real sky, but on a cloudy night if you have software such as Skytools you can simulate finding objects. This method will help you know what stars to hop from and what stars will be in the field of your finder. It won’t replace the real thing but on a cloudy night it is a great alternative.
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