How to Shop for Telescopes (2020) + Bonuses
Shopping for telescopes can seem intimidating, but by using these pointers you can approach it with more confidence!
Supplementary Material
Telescope Shopping Quick Guide
I’ve Read the Quick Guide — Now I Want to Know More:
A more in-depth explanation of what to look for and why when shopping for telescopes.
Aperture Size
The aperture of a telescope is what gathers the light from the object you’re viewing. The light is then funneled into the eyepiece of the telescope, where you observe the image. In refracting telescopes, the aperture is a lens that’s at the front of the telescope. In reflecting telescopes, the aperture is a mirror that’s in the back of the telescope. Aperture size refers to the size of this objective mirror or lens.
The larger the aperture of a telescope, the more light the telescope collects. Think of it like how your electronic devices — televisions, computer monitors, smart phones — display a better picture on their screen the more pixels that screen has. A television for example, is considered high-definition when its screen has a dimension of 1920x1080 pixels or more. Similarly, the more light a telescope collects, the more detail of the object you have the potential to see. So — for all intents and purposes — the bigger the aperture of your telescope, the better!
Focal Ratio
Focal ratio is the relationship between the size of the aperture and the focal length (distance between the aperture and where the light focuses to a point) of the telescope. The longer your focal length, the tighter your view of the sky will be and the better you’ll be able to resolve objects that appear close together, like Albireo A and Albireo B. The shorter your focal length, the wider field view you’ll have of the sky. Focal ratio is simply expressed as F=f/D, where “F” is focal ratio, “f” is focal length, and “D” is the diameter of the aperture. The longer your focal length, the greater the focal ratio will be. The shorter your focal length, the lesser the ratio will be.
If I have an aperture with a diameter of 70mm, and a focal length of 700mm, I would have a focal ratio of: F=700mm/70mm=10
However, for whatever reason, telescope companies represent a focal length of 10 as F=f/10, instead of just F=10. This is mathematically inaccurate but is how they describe it.
Because focal ratio describes how much or how little a telescope shows, when shopping for a telescope, it’s important to know what you hope to see with it. Focal ratio is an easy way to determine if a particular telescope has the ability to display what you hope to observe.
Focal Ratios and their uses:
F=f/10 and higher is good for planets and their features, along with a tighter view of the Moon’s surface
F=f/7 and lower is good for a full view of the moon and for a wide view of star fields, like if you wanted to use your telescope to photograph our Milkyway Galaxy.
Any ratio between F=f/7 to F=f/10 is good for both. For your first telescope, I usually recommend a telescope around this range.
Both images were taken with a 70mm aperture. The main difference is their focal ratios.
Jupiter taken with a 70mm reflecting telescope with a focal ratio of F=f/3.95
This is the same image as above — it is simply zoomed in to simulate using an eyepiece with a smaller focal length to magnify the already blurry image
Magnification
Just as the body of your telescope has a focal length, the eyepiece of your telescope has a focal length as well. Magnification is simply the relationship between your telescope’s focal length and the focal length of your eyepiece. Most telescopes come with their own set of eyepieces (In my experience, usually two eyepieces come with a telescope). Magnification is used to produce a larger, more zoomed-in image from your telescope. The smaller the focal length of your eyepiece, the more zoomed-in your image is. An eyepiece with a focal length of 20mm is what you’d use to first find a planet in the sky, and then to “zoom in” on that planet you’d switch to an eyepiece with a shorter focal length.
How-ever, you can only magnify — or “zoom-in” on — an image so much before it gets blurry. Magnifying an image only allows you to better see detail if the aperture and focal length captured and resolved that detail. That’s why it’s important to consider the aperture and focal length of the telescope first, rather than the magnification of the eyepiece.
Some off-brand telescope companies will try to sell their telescopes by emphasizing magnification in their advertisements. These are companies you should avoid, as they are simply trying to trick you into buying a telescope incapable of displaying a detailed image. They likely do this because it is easier to manufacture a high-magnification eyepiece than it is to manufacture a quality telescope, and because most people assume that an eyepiece with higher magnification will make the moon and planets easier to see, like a magnifying glass makes small text easier to read.
Don’t be fooled: shop for aperture size first, focal length second, and magnification last.
Buying on Brand
If you grew up with a parent, or grandparent who lived during the great depression, you likely learned the lesson “Buy cheaper -- you won’t notice the difference.” Which isn’t necessarily a bad thing! I get it — we buy “Marshmallow Mateys” instead of Lucky Charms, and I can’t tell the difference. But for telescopes, we buy on-brand only.
Name brand telescope companies (like Celestron and Meade) built their trusted reputation by manufacturing quality telescopes. Today, they have to maintain that reputation by continuing to deliver quality products. Now, this does tend to make their products slightly more expensive, but you truly do get what you pay for when it comes to telescopes.
Refractor telescopes (telescopes that use lenses to focus light) suffer from a unique type of distortion called “Chromatic Aberration”. This is where different wavelengths (or colours) of light split up when passing through a lens. Name brand companies, like Celestron and Meade, can lessen the chromatic aberration via special coatings or corrective lenses. They have the money, engineering capabilities, and drive to do so. How-ever, off-brand companies tend to not to correct chromatic aberration because of the added cost. Even worse, off-brand companies often use plastic lenses in their telescopes rather than glass, making the uncorrected chromatic aberration even more pronounced.
I understand: you want to give someone the gift of exploring outer space, but you don’t want to break the bank. But I promise you, high quality doesn’t necessarily mean high price tags. You just have to know what to look for. If you refer to the image in the aperture size section — the image of the Moon taken with the 70mm reflecting telescope is only ~$60.00 on Celestron’s website -- comparable in price to many of the off-brand refractors that will yield images of much lower quality.
Which leaves me with one final note:
DON’T BUY YOUR TELESCOPE FROM WALMART
This image was taken with a 40mm Vivitar refractor which contains a plastic lens — chromatic aberration is very noticeable around the numbers.
This image was taken with a 70mm Celestron (on-brand) refractor which contains a glass lens — chromatic aberration is barely noticeable at all.
Whilst doing research for this show, I did some telescope price comparisons between Walmart vs. Celestron, and what I found was disappointing and shocking:
Walmart Selling a Celestron AstroMaster 90AZ Refractor for $391.66
Walmart Selling a Celestron AstroMaster 130EQ Reflector for $537.85
Celestron Pricing a Celestron AstroMaster 90AZ Refractor for $259.95
Celestron Pricing a Celestron AstroMaster 130EQ Reflector for $299.95
(This model contains a motor driven mount, which is more expensive than the base model that Walmart is selling, but Walmart’s price for the base model is so outrageously priced that they’re selling the base model for more than Celestron is selling the motorized model.)
From what I’ve found, Walmart consistently sells name brand telescopes for outrageous prices, compared to the manufacturer and competing mega-stores like Target. Since we, at Fly Science Guy Star Shows, suggest shopping on-brand for your, or your loved one’s, first telescope — we suggest avoiding Walmart for this product and comparing prices to the manufacturer’s website.
