Is 50mm or 70mm Better for a Beginner Telescope?
Let me get straight to the point: if you’re choosing between a 50mm and 70mm beginner telescope, the 70mm is almost always the better choice. It gathers about twice as much light as the 50mm, which means you’ll see noticeably brighter, clearer images of the Moon, planets, and even some deep-sky objects. But here’s where things get interesting: bigger isn’t always better in every situation, and understanding why will save you money and frustration.
Why Aperture Matters More Than You Think
The number before “mm” refers to the aperture, which is simply the diameter of the main lens or mirror that collects light. Think of it like comparing a bucket to a bathtub when catching rainwater. The 70mm telescope is the bathtub, it catches significantly more light, and in astronomy, more light equals more detail and fainter objects becoming visible.
Here’s something most beginner guides won’t tell you: the difference between 50mm and 70mm represents a jump from seeing roughly 10.2 stellar magnitude to 11.0 stellar magnitude. That might sound like technical mumbo jumbo, but it translates to thousands more stars becoming visible to your eye. On Jupiter, a 50mm will show you the planet’s cloud bands and maybe three moons, while a 70mm will reveal more subtle atmospheric details and make all four Galilean moons pop against the dark sky.
The Real-World Performance Gap
I remember lending my 50mm refractor to a friend’s kid who was just getting into stargazing. Within two weeks, he was back asking about upgrades because Saturn’s rings looked “kind of blurry” and the Orion Nebula was “just a fuzzy blob.” Switch him to a 70mm scope, and suddenly astronomy became exciting again. The rings had definition, and that fuzzy blob showed actual structure.
The light-gathering power difference is quantifiable. A 70mm telescope collects about 96% more light than a 50mm. That’s not a marginal improvement, it’s transformational. When you’re looking at the Andromeda Galaxy, the difference between “I guess I can see something there” and “Wow, I can actually see the galaxy’s shape” often comes down to that extra 20mm of aperture.
What About Portability?
Now, here’s where the 50mm makes its case. These telescopes typically weigh between 1.5 to 2.5 kg (3.3 to 5.5 lbs) fully assembled, while 70mm scopes often tip the scales at 3 to 4 kg (6.6 to 8.8 lbs). If you’re a younger observer or someone who plans to hike to dark-sky sites regularly, that weight difference matters.
But let’s be honest: most beginners use their telescope in the backyard or on a balcony. That extra kilogram isn’t a dealbreaker when you’re walking 15 meters from your back door. Where portability becomes genuinely important is if you’re travelling by plane or need to pack everything into a small car alongside camping gear.
The Magnification Myth You Need to Ignore
Here’s where telescope marketing gets sneaky. You’ll see 50mm scopes advertised with “525x magnification!” in big bold letters. Sounds impressive, right? It’s basically worthless. The maximum useful magnification for any telescope is roughly 2x per millimeter of aperture, sometimes quoted as 50x per inch. That means a 50mm maxes out at around 100x before images become dim and blurry, while a 70mm can handle 140x and still deliver sharp views.
Those astronomical magnification claims rely on terrible quality eyepieces that make everything look like you’re viewing it through a frosted shower door. A 70mm scope at 70x will outperform a 50mm at 100x every single time because the image remains bright and crisp.
When a 50mm Actually Makes Sense
I’m not here to trash 50mm telescopes entirely. They have legitimate uses. If you’re buying a scope specifically for a child under 10 years old who might lose interest in three months, the lower price point of a 50mm makes financial sense. You’re looking at roughly $80 to $150 for a decent 50mm versus $150 to $250 for a comparable 70mm.
The 50mm also shines, pun intended, for casual daytime terrestrial viewing. Want to watch birds at the feeder or check out boats on a lake? A 50mm refractor works perfectly fine and sets up in seconds. Some 50mm scopes also come with erect-image diagonals that show right-side-up images, which is less common on astronomy-focused 70mm models.
The Temperature Factor
Here’s an interesting consideration that rarely gets mentioned: thermal equilibrium. A 70mm telescope needs roughly 30 to 40 minutes to adjust to outside temperatures, while a 50mm typically reaches equilibrium in 20 to 25 minutes. When you’re standing outside in 5°C (41°F) weather, that difference matters. The larger optics in a 70mm take longer to stabilize, and until they do, you’ll see wavy, distorted images as air currents move across temperature gradients in the tube.
That said, once both scopes reach equilibrium, the 70mm delivers noticeably superior views. It’s like waiting an extra 15 minutes for a restaurant table at the better place versus settling for the mediocre spot with no wait.
Build Quality and Mounts: The Hidden Variables
This is where things get messy. A well-made 50mm on a solid alt-azimuth mount will outperform a cheap 70mm on a shaky tripod that vibrates every time you touch the focus knob. I’ve seen this repeatedly with department store telescopes that prioritize aperture but cut corners everywhere else.
Look for these quality indicators regardless of aperture: an adjustable, sturdy tripod with leg braces, a mount that moves smoothly without wobbling, and at least two eyepieces (typically 25mm and 10mm). The telescope should feel substantial but not top-heavy. If the whole thing shakes when you breathe near it, walk away no matter how big the aperture is.
Optical Design Considerations
Most beginner scopes in these apertures are refractors, which use lenses rather than mirrors. That’s generally good news because refractors need virtually no maintenance and deliver crisp, high-contrast views of the Moon and planets. However, budget refractors often show chromatic aberration, which appears as purple or blue halos around bright objects like Venus or the Moon’s edge.
Interestingly, chromatic aberration becomes slightly more noticeable in larger apertures with short focal ratios. A 50mm f/10 refractor might show less color fringing than a 70mm f/5, even though the 70mm gathers more light overall. For planetary viewing specifically, a well-made 50mm with good optics sometimes edges out a mediocre 70mm, but this is the exception rather than the rule.
Making Your Decision: The Bottom Line
If budget allows and you’re genuinely interested in astronomy beyond casual glances at the Moon, buy the 70mm. The performance improvement justifies the extra cost and weight for 90% of beginners. You’ll see more objects, enjoy brighter views, and be less likely to outgrow the telescope within months.
Choose the 50mm only if you’re on a strict budget (under $100), need maximum portability for specific reasons like backpacking, or you’re testing the waters with a young child whose interest might evaporate quickly. Even then, consider whether saving up another month or two for the 70mm might serve you better long-term.
Here’s my honest take after helping dozens of people choose their first telescope: nobody ever complained that their beginner scope gathered too much light. But I’ve heard countless stories of people upgrading from 50mm to 70mm or larger within a year because they caught the astronomy bug and wanted better views. Starting with the 70mm often means you’ll stick with it longer before feeling the upgrade itch.
What to Expect From Each Aperture
With a 50mm telescope, you’ll clearly see lunar craters down to about 7 to 10 km across, Jupiter’s cloud bands and moons, Saturn’s rings (though they’ll look thin and somewhat dim), and Venus showing phases. The Pleiades star cluster looks beautiful, and you’ll resolve it into individual stars. The Orion Nebula appears as a fuzzy patch with hints of structure. That’s honestly not bad for an entry-level scope.
Step up to a 70mm telescope, and suddenly those lunar craters become sharper with more fine detail, you’ll spot smaller features around 4 to 6 km across under good conditions. Jupiter’s Great Red Spot becomes visible during transits, and Saturn’s Cassini Division (the gap in the rings) pops into view on nights with steady atmospheric conditions. The Orion Nebula shows definite structure with its characteristic wing-like shape, and you’ll start picking out colors in brighter stars. You’re also able to hunt for more challenging targets like the Ring Nebula and various globular clusters.
The viewing experience shifts from “that’s neat” to “that’s legitimately impressive” with that extra aperture. Is it twice as good? Not exactly, but it’s enough better that you’ll notice immediately.
The Path Forward
Whichever aperture you choose, remember that the best telescope is the one you’ll actually use. A 50mm that gets set up twice a week beats a 70mm that stays in the closet because it feels like too much hassle. Start learning the sky with whatever scope you get, join a local astronomy club if possible, and focus on developing your observation skills.
The universe isn’t going anywhere, and both apertures will show you enough wonders to keep you busy for months. But if you’re asking which one will keep you satisfied longer and show you more of what’s out there, the 70mm wins that contest decisively. It’s the telescope I recommend to friends, family, and anyone genuinely curious about exploring the night sky. If wanting to know more, why not take a look at our top beginner telescope picks.
