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How to Use a Red-dot Finder Scope for Astronomy

Posted by Ryan DeLange on

If you’re having a hard time getting anything to show up in your telescope’s eyepiece, then you probably just need to learn to align and use your red-dot finder scope.

Most new astronomers go through this frustration. Don’t worry, this guide will give you the know-how, and with a little practice, you’ll get the hang of it.

First off, let’s take a look at the instrument. A red dot finder scope has no magnification power. It simply transposes a tiny red dot onto the image you see when you look through the finder scope. Many red dot finders come with a knob that adjusts the brightness of the dot. All red dot finders have two direction adjustment knobs, one for altitude (up and down) and one for altazimuth (right and left).

Here’s how you use it

During daylight hours or at night?

Practicing on terrestrial objects during daylight hours is ideal for a couple of reasons. First, there are plenty of bright, easily identifiable targets for you to practice on. Second, it is easier when you have a visual frame of reference, rather than trying to locate objects separated by light-years of darkness.

If your red dot isn’t bright enough to show up during broad daylight, then wait until dusk - after sunset but while land objects are still visible. Some people suggest practicing with the moon at night, but there is limited variety, and it might not even be up when you want to get started.

Center an object in the telescope’s eyepiece

Start by choosing an object that is fairly large, bright and easily identifiable in the middle distance, like a telephone pole or the point of a roof. Looking through the eyepiece of your telescope, adjust the telescope so that that object is directly in the middle of the image.

Using a low-power eyepiece will make this easier, maybe 20mm or above (the higher the focal length of the eyepiece the lower the power). If the magnification is too high, then it will be more difficult to find objects and tiny adjustments will exaggerate the movement in the eyepiece.

Align the red-dot finder scope

Now, let’s look through the red dot finder scope. The goal is to get the red dot to line up directly on top of the same object. Use the altitude and azimuth adjustment knobs until the red dot is in the right place. Get used to keeping both eyes open, so that one eye is looking through the finder and the other is able to scan the whole sky.

Test it

At this point, your finder scope should be aligned. Now choose another object. This time, look through the red dot finder first and move the telescope so that red dot is on the object. Then look through the telescope’s eyepiece. If everything is aligned properly, that very same object should be visible in the middle of the image.

This skill is one of the most important ones for the astronomer to master. It’s a bit tricky and takes some getting used to. Do you have any questions or tips about using red-dot finder scopes? Your comments below would be helpful.

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As a higher-level amateur, I was looking for a decent scope & mount that I can modify for my needs. The 130mm Newtonian scope fits my needs quite well. It comes with a 25mm eye piece--which is great. I would consider purchasing other eye pieces at the same time to give you a variety of magnification options. I'd recommend something like a 12mm and 8, or 6mm eye pieces to complement the 25mm. Getting a 2X Barlow will double your eye piece viewing options. The higher number will give you a wider view, smaller number a tighter, more magnified view. In order to just resolve the bands & zones of Jupiter, I need to use an 8mm eyepiece. For exploring Lunar geography, or seeing the Galilean Moons, the 25mm is sufficient. Saturn is just discernable, until you switch-out the eye piece for a 12mm, or smaller. The heavy & stable tripod mount is easy to set up, and the large rotation nobs allow you to smoothly track your subject as the Earth rotates. The Red Dot spotting site is dead-on accurate (once you dial it in). If you want a good, intermediate telescope: one that's neither too cheap, nor one that's too expensive, the 130mm Newtonian should fit your needs quite well. (Image of the Moon has been rotated and adjusted with photo software).