WELCOME TO

2023

Fellow Stargazers!

By: Katherine Miller

I have been on hiatus for the past few months, but I am so excited to be back! I am going to pick up where I left off. In my previous article, I discussed the benefits of using a refracting telescope. In this article, I will discuss Reflectors (and somehow keep the article under 500 words…wish me luck!).

Unlike a refractor which uses glass elements, reflectors are telescopes that use mirrors to reflect light to an eyepiece or digital aid. The first reflecting telescope, known as a Newtonian, was invented by Sir Isaac Newton in 1668. However, the concept of using mirrors instead of glass had been discussed for some time by other prominent historical figures such as Giovanni, Galileo, Niccolo Zucchi and James Gregory.

Reflecting telescopes generally use two mirrors, a concave primary mirror and a flat secondary mirror. Light bounces off the larger primary mirror and onto the smaller secondary mirror, which directs the light into an eyepiece or camera sensor. However, some reflecting telescopes don't have a secondary mirror. From the

1999

first designs until the 1800s, the primary mirror was made entirely of metal. However, modern versions use a piece of glass with a thin layer of highly reflective aluminium on top. Reflecting telescopes are excellent for visual astronomy, and amateur and professional astrophotography. Their larger apertures offer better resolution and more lightgathering power. They also have no chromatic aberration. Like refracting telescopes, reflectors have some drawbacks and can suffer from optical issues, such as coma. Coma is when stars appear comet-like towards the edge of an image and occur due to light falling inwards from the optical axis. A field flattener (a glass lens that corrects field curvature) can fix this problem. Another issue is diffraction spikes. Which occurs due to the obstruction of the path of light by the mechanisms (the spider) that support the secondary mirror. Though, many astrophotographers like effect, and some even use string over the front of their telescopes to create them in images. Another drawback to reflecting telescopes is the need to collimate. However, this is a simple procedure and after a bit of practice can be completed quickly. If you plan on travelling with your telescope, reflectors might not be the best option for you. Collimation will need to be checked when you reach your destination as the bumpiness of the road may bring the mirrors out of alignment. Longer focal lengths can be quite large and some designs, such as the Dobsonian, can be bulky and heavy. Reflectors are often a lot cheaper than refractors of the same focal length and have faster apertures. There are many different types of reflecting telescope designs such as Newtonian, Dobsonian, CDK Cassegrain, Schmidt Cassegrain; and Maksutov Cassegrain. If you are a beginner to astronomy and want to do some casual viewing with the family. I would recommend starting with a Dobsonian. There are adapters you can use to take photos through the eyepiece via a mobile phone. Dobsonians will provide you and your family with magnificent views of the planets and bright nebulae.

There is a small learning curve involved, such as collimation and star alignment (if you choose one with built-in go-to functions).

Cassegrains and large Newtonians are best suited (but not limited to) observatories and backyard set-ups. They’re great if you plan to image deep-space objects like nebulae because of their light-gathering abilities. Their focal lengths and apertures are perfect for sharp planetary images too. However, as the saying goes, the best telescope is the one you can afford. No matter the design, all will provide you with the ability to view and photograph the moon, planets, stars and space.

Don’t forget to grab a pair of binoculars and look towards the northern night sky near the constellation Auriga from February! Comet C/2022 E3 (ZTF) will be visible for the first time in 50,000 years!

I hope you’ve found this helpful! If you want to discuss anything, or want to share your images, email me at astrogirl. au@mail.com