Red-Dot Finders for Telescopes: How They Work and Why a Rifle Sight Is Not the Same Thing

The earlier post on this site was a used-sale listing for a Barska 1x multi-reticle electronic red-dot sight with a built-in rail mount (model AC10632), a sight designed for firearms. That item does not belong on an astronomy site, so this rewrite replaces it with a guide to red-dot finders made for telescopes. These work on the same basic principle and are one of the most useful accessories a beginner can have.

What is a finder?

A telescope‘s main view covers only a tiny patch of sky, so pointing it at a target by eye is hard. A finder is a small aiming device mounted on the telescope tube. Celestron’s guide to finderscopes explains that once it is aligned with the main telescope, the finder becomes a mini version of your telescope’s view, helping you centre a target before switching to the eyepiece.

Types of finders

Celestron describes three main types:

• Red LED finders project a red dot or reticle onto a viewing screen, so you can aim with both eyes open.
• Optical (straight-through) finders are small telescopes with some magnification and crosshairs.
• Right-angle correct-image (RACI) finders bend the view by 90° for comfort and show the image the right way up.

How a red-dot finder works

Celestron’s StarPointer is a typical example. According to Celestron:

• It has 1x magnification, so there is no zoom.
• It gives a very wide field of view.
• It keeps the sky the right way up and correct left to right, matching what you see with your eyes.
• An LED creates a red dot, superimposed on a viewing screen.

You look through the window, place the red dot on the star or planet you want, and if the finder is aligned, that object will be centred in the telescope’s eyepiece.

Celestron’s StarPointer specifications include a 23 mm lens, a CR2032 3V battery and mounting brackets for Schmidt-Cassegrains and small telescopes with a dovetail or screw holes.

Why not just use a rifle red-dot sight?

A firearm red-dot sight, like the Barska model in the original listing, also uses an illuminated dot on a window. But it is made for a different job:

• Mounting: firearm sights are built for weapon rails. Telescopes usually use a finder shoe or dovetail base, so a rifle sight would need an improvised adapter.
• Design goal: a telescope finder is built for the job. Celestron says the StarPointer’s adjustable red dot is bright enough to see day or night, and that it attaches to just about any telescope and even works with astronomical binoculars and spotting scopes.
• Purpose: telescope finders come with brackets designed for telescopes, as Celestron’s StarPointer does.

For astronomy, a purpose-made telescope finder is the simpler and safer choice.

Aligning your red-dot finder

Celestron notes that aligning a finder is easy and can be done in daylight:

• Put a low-power eyepiece in the telescope.
• Point the telescope at a distant object such as a treetop, rooftop or pylon. Never point it at the Sun.
• Centre the object in the eyepiece.
• Turn on the red-dot finder and use its adjustment knobs to move the dot onto the same object.
• Check it again at night on a bright star and make small corrections if needed.

Using it at night

• Use a dim dot. If your finder has a brightness control, a dimmer dot is easier to use against faint stars.
• Keep both eyes open. This makes it easier to match the dot with the sky.
• Start with bright targets. The Moon, bright planets and the brightest stars are easy to aim at.
• Switch off after use. This saves the battery. Carry a spare CR2032 on cold nights.

Red-dot finder or optical finder?

• Choose a red-dot finder for quick aiming, a sky view that matches your eyes and simple operation. It is ideal for beginners.
• Add an optical finder if you star-hop to faint objects, because its magnification shows fainter stars than you can see with your eyes.

Many observers use both: a red-dot finder for rough aiming and an optical finder for precise centring.

The bottom line

A red-dot finder is a simple, low-cost accessory that makes any telescope easier to point. Use one designed for telescopes rather than a firearm sight, align it in daylight, and turn the dot down at night for best results.