What is a finderscope and how do you set one up?

A finderscope is a simple but invaluable accessory that attaches to your telescope. Find out what they are, how to set one up, and whether they are still useful.

Finderscopes and mounts are basic accessories that will help you - and your telescope - navigate the night sky and locate celestial targets. Credit: BBC Sky at Night Magazine

A finderscope is a simple but invaluable accessory that attaches to your telescope. The smaller optical tube provides a wide field of view to help you locate celestial objects before observing them through your main telescope, but it must be aligned accurately to your telescope before use.

Advertisement

To set up a finderscope, start aligning in the daytime by finding a very distant object using your telescope, centring that object in your telescope eyepiece as accurately as you can.

When doing any sort of observation during the day, make sure not to look directly at the Sun without specially-designed solar filters, or this could seriously damage your eyesight. For help with this, read our guide on how to polar align using the Sun.

Without moving the telescope, observe through the finderscope and centre its crosshair on the same object by adjusting the three alignment bolts that hold the finderscope in its cradle.

Read all of our finderscope reviews or follow our DIY Astronomy guides to make a smartphone finderscope or a finderscope illuminator.

Sky-Watcher 9x50 right-angle finderscope
Sky-Watcher 9×50 right-angle finderscope

Are finderscopes redundant?

Words: Paul Money

Once upon a time we were lost without them. The trusty optical finderscope allowed us to get a wide field of view to visually home in on targets, or help us star hop to the next one.

Now don’t get me wrong, in terms of any basic or manual telescope, the finderscope still serves that purpose very well, and is a necessary piece of kit.

But when it comes to GoTo systems, it becomes a little less clear just how useful a finderscope can be.

Man looking at the stars with telescope beside him. Credit: iStock
Are finderscopes redundant, or are they still a vital aspect of a telescope setup? Credit: iStock

“What?” I hear you cry, “you still need it for the initial alignment for the GoTo to work accurately don’t you?” Well I think the answer is yes and no to that.

If your initial polar alignment is rough or you have a system that you need to move around a lot, perhaps for public outreach, then I agree that the finderscope remains useful, but only for the alignment phase of setting up.

After that, if your polar alignment and star alignment is accurate then your target should always be in the view of a wide field eyepiece if not bang in the centre.

However, if you are able to conceive a permanent setup for your mount, you can get polar alignment very accurate indeed.

William Optics 7x50 straight-through finderscope
William Optics 7×50 straight-through finderscope

Once done, you will likely find you hardly ever use the finderscope, as the target should be in the centre of the view or imaging system you are using every time.

But today manufacturers have spotted an opportunity amongst all this, and we are now seeing finder/guidescope combinations.

In other words, the fact that many astronomers are now using the finder as a guidescope for deep-sky astrophotography may well mean we haven’t seen the last of the finderscope just yet!

Advertisement

Email Steve your astronomy queries to scopedoctor@skyatnightmagazine.com.