Smartphone Telescopes and Phone Zoom Lenses: What They Can Really Do (and a Better Way to Photograph the Moon)

Small monocular “telescopes” that clip onto a smartphone are sold as a cheap way to zoom in on wildlife, sport or the Moon. This page replaces an earlier shopping post about these attachments with a plain-English guide. It covers how they work, what the large magnification figures on the box mean, and what really works for photographing the night sky with a phone. We do not recommend a specific product, because there are many near-identical models and their specifications are rarely independently tested.

What a phone telescope attachment is

Most kits contain three parts:

• A small monocular, a short telescope with an objective lens at the front and an eyepiece at the back
• A clamp that holds the monocular over the phone’s camera lens
• A small tripod to keep everything still

The phone’s camera then takes a picture of the image formed by the monocular’s eyepiece. Astronomers call this “afocal” photography, and it is exactly the same idea as holding a phone up to a real telescope’s eyepiece.

About those big magnification numbers

Listings often advertise figures such as 80x or 100x or more. Treat these numbers with caution:

• Magnification alone does not make a sharp image. The front lens of a pocket monocular is small, so it gathers limited light, and very high power with a small lens gives a dim, blurry picture.
• High magnification also magnifies every shake. Without a solid tripod, the image jumps around.
• Phones have several camera lenses and may switch between them as you zoom. Sky at Night Magazine warns that this can throw an adapter out of line, so make sure the attachment sits over the right lens.

A good rule is to judge a device by its lens diameter and build quality rather than by the magnification printed on the box.

The better approach: your phone plus a telescope or binoculars

NASA’s Night Sky Network and BBC Sky at Night Magazine both describe the same simple method for taking astronomy photos with a phone:

• Point your telescope at the Moon and focus it by eye first.
• Hold your phone’s camera lens up to the eyepiece, centred and close. Moving it slightly forwards and back helps you find the full circle of light.
• Better still, use a phone adapter that clamps the phone to the eyepiece. NASA notes you can buy or make one, and it also lets you share the live view with others.
• Take lots of photos with different settings and keep the best.

Sky at Night Magazine points out a big advantage: you do not need to remove the eyepiece, so you can switch quickly between looking and taking pictures with any telescope used for visual observing.

Camera settings that help

The Moon is very bright, and automatic phone settings often turn it into a white blob. NASA’s lunar photography guide and the astronomy guides above suggest:

• Take manual control. Use a “Pro” or manual mode, or a camera app that lets you set focus and exposure yourself.
• Lower the exposure. Turn the brightness down until surface details appear.
• Lock focus. Tap on the Moon and lock focus so the phone does not hunt.
• Avoid shaking. Use the self-timer or a remote shutter so your finger does not move the phone.
• Avoid heavy digital zoom. Digital zoom only enlarges pixels. Sky at Night notes that zoom can increase magnification through the same eyepiece, but too much makes images soft.

What you can realistically capture

• The Moon is by far the easiest target. Even a modest telescope and a phone can show craters along the line between light and shadow.
• Bright planets appear small. Jupiter’s moons and Saturn’s rings are possible through a telescope with patience, but expect tiny images.
• Daytime subjects such as birds and distant landscapes are where clip-on monoculars are most useful.
• Faint galaxies and nebulae generally need long exposures and tracking mounts, and are beyond a clip-on monocular.

Shopping checklist

If you still want a clip-on phone telescope:

• Prefer a model that states its objective lens diameter in millimetres.
• Check that the clamp fits your phone’s size and camera layout.
• Make sure a sturdy tripod is included, or use your own.
• Be sceptical of extreme magnification claims and of photos in listings that look too good to be true.

The bottom line

A clip-on phone telescope can be fun for daytime nature viewing, but it is not a substitute for a real telescope. For the night sky, the best results come from holding or clamping your phone to the eyepiece of a telescope, then taking manual control of exposure and focus. Start with the Moon, take many photos, and keep practising.