The Biggest Lie in Telescope Marketing

[00:00:00]If you've ever spent any time looking at budget or entry-level telescopes online or in department stores, you might have noticed a shift in how they're marketed.

[00:00:09]A decade ago, department stores routinely made crazy claims such as 600 times magnification, and this is for a tiny plastic lens telescope. Today, manufacturers have dialed the numbers back to sound more reasonable. Now, you usually see claims of around 300 times magnification, and while that sounds more plausible, the reality hasn't really changed. This is still an unusable number designed to sell scopes to beginners, and it can set people up to fail.

[00:00:37]Here is how that math actually looks. If you buy a standard 70 mm refractor with 400 mm focal length, it will often come with a 4 mm eyepiece that gives you around 100 times magnification.

[00:00:51]And to push that number higher for the product listing, they'll include a cheap 3 times Barlow lens. And when you stack it all together, that will give 300 times magnification, so they can get away with putting that figure on the box. is technically correct on paper, but the physics doesn't really add up.

[00:01:08]As a general rule, the absolute maximum useful magnification for a telescope is about twice its aperture in millimeters.

[00:01:16]This rule works well for lenses and mirrors up to around 100 mm or 4 in in diameter.

[00:01:23]For a 70 mm lens, that caps the theoretical limit to 140 times magnification under perfect seeing conditions. Realistically, on a wobbly budget tripod and entry-level optics, the image is going to degrade, so realistically, we can expect sharp views to around 80 to 100 times. If you force a 70 mm aperture telescope to 300 times, we reduce the exit pupil, the size of the light that goes into your eye, to less than a quarter of a millimeter, and the view then becomes a bit dim and blurry, and you lose all usable detail.

[00:01:58]If you're helping someone pick out a telescope or you're looking for one for yourself, the best advice is to ignore the magnification specs completely.

[00:02:06]Magnification is just a function of whatever eye piece you decide to use.

[00:02:11]Instead, focus on aperture, optical quality, mount stability, and the atmospheric seeing conditions. A sharp, bright view of Jupiter at 100 times is a greater experience than a shaky, dark, blurry view at 300 times. I mentioned the two times aperture rule, which holds for smaller telescopes that are around around 100 mm or 4 in.

[00:02:33]So, a 100 mm lens telescope puts a theoretical upper limit at about 200 times magnification.

[00:02:40]In many cases, that's also where the Earth's atmosphere becomes a limiting factor.

[00:02:46]The issue isn't the telescope, it's the air above it. Atmosphere turbulence distorts the image, so high magnifications don't reveal more detail.

[00:02:55]That's the main reason why professional observatories are built on high mountains and why space telescopes are so important. They're not just using better equipment, they're getting above the atmosphere that blurs everything in the first place. Let's say that you do have great optics, a bigger lens or mirror, and a perfectly still night.

[00:03:15]There is still one critical component that can completely ruin your view, and that's the mount.

[00:03:21]When you are looking at a budget telescope listing, all the focus is on the optical tube. The tripod and the mount underneath it are usually treated as an afterthought. But, at high magnifications, your mount is oddly just as important as your lens or mirror.

[00:03:38]When you zoom in to an object at 150 times or 200 times magnification, you aren't just magnifying the target, you are magnifying everything. So, a gentle breeze can wobble like an earthquake in the eye piece, and the same goes for touching the focus so when you're focusing the image.

[00:03:57]If you have a shaky lightweight plastic mount, it can take 5 to 10 seconds for the vibrations to settle down every time you try every time you touch the telescope.

[00:04:06]If you're trying to track a planet across the sky manually, you can spend more time waiting for the image to stop shaking than you are observing. So the formula for a great view is simple really. It's It's not about the magnification number on the box. If you want the best possible experience under the stars, remember these four pillars.

[00:04:26]First of all, we've got aperture. Look for a decent size mirror or lens so you can collect plenty of light and resolve finer detail. The two times aperture rule where magnification maxes out at roughly two times the aperture in millimeters.

[00:04:41]The atmosphere. Remember that the air above us dictates the view. Most nights a crisp view at 100 times will be an unusable view at 250 times.

[00:04:52]Stability. A solid mount is what keeps your target still enough to enjoy it.

[00:04:56]Seeing things clearly is always better than just bigger.

[00:05:00]So that's it for this video. Thanks for watching. A big thank you to my channel members and Patreons and until next time remember to tell those clouds to sod off.