Binocular Astronomy
Written by Tammy Plotner
Are you ready to start practicing binocular astronomy? While using binoculars to study the stars is quite easy to learn and doesn't require a whole lot of sophisticated equipment, there are a few simple guidelines that will help increase your enjoyment of binocular astronomy. Let's take a look at them…
How To Choose Binoculars For Astronomy: Before you select what pair of binoculars you will use, there are a few simple things you need to know and terms you will encounter. Eye relief and exit pupil is important! Choose binoculars that offer long eye relief – because this is the distance they will need to be away from your eyes to focus. You don't want your eye crammed against the lens! Exit pupil is also best between 5-7mm, since even the best of human eyes can't accept much more than 5.
Another important consideration is coatings. Ruby coatings are not good for astronomy applications – chose models that offer full-coatings instead. The field of view is also important. While it doesn't affect what you see, knowing the field of view will help you aim your binoculars more accurately when you practice binocular astronomy.
Binocular Astronomy – Roof Prism Binoculars: Roof prism binoculars provide for a compact, lightweight body, but they are not the prime choice for binocular astronomy. This design requires phase correction coating to provide a clear image. In phase coating, a special material is added to eliminate distortion along the roof edge of the prism, and without it a clear edge-to-edge image could not be produced. Roof prism binoculars also require that incoming light be folded four times – a technical design which means they not only do not perform as well on dim subjects, but require absolute precision in manufacturing.
Binocular Astronomy – Small Porro Prism Binoculars: A good choice for all purpose binocular astronomy is the small porro prism model. The traditional Z-shaped porro prism design is well suited to astronomy and consists of two joined right-angled prisms which reflects the light path 3 times. These smaller, lighter weight units have numbers like 5X25, 5X30, 10X30 and 10X50. The first number is the amount of magnification the binoculars provide and the second number is the aperture opening. From a dark sky site, practicing binocular astronomy with a small porro prism model will provide you with an opportunity to see bright star clusters and nebula – as well as brighter galaxies and comets. Even inexpensive models can perform very well.
Binocular Astronomy – Large Porro Prism Binoculars: If you are serious about practicing binocular astronomy, a good suggestion is to start off with a model well suited to deep sky… and that means a larger aperture, or a higher second number. However, this also means increased weight and size… decreasing your ability to hold them steady with just your hands. Larger binocular astronomy models start off in about the 10X50, 9X63, etc. range and run the gambit up to 90mm or larger. As the second number increases, so does your ability to find progressively fainter objects, but be wary of too much magnification since you will need to be very steady to use it. This size is perfect for most astronomy applications, such as the Messier objects and most comets.
Binocular Astronomy – Astronomy Binoculars: Binoculars that have reached the 16X80, 20X80, 25X100, etc. are considered true astronomy binoculars. Their size and weight will require a stabilization unit, such as a mount and tripod to make them effective. Able to gather as much light as a small refractor telescope, these models will give you a deep, rich view! You'll enjoy extended nebula, faint galaxies, fainter comets and well resolved deep sky objects.
Binocular Astronomy – Binocular Telescope: Binocular telescopes exceed the 125mm aperture size and differ from astronomy binoculars in the respect that they have interchangeable eyepieces and the ability to add star diagonals to assist in viewer angle comfort. They are permanently mounted and require a tripod or pier to be used. What's the view like? Heavenly! At this size, a binocular telescope is able to provide wide field views and crisp, well resolved images. They are well suited to comet hunting!
Binocular Astronomy – The Monopod: Once you have chosen your binoculars, you'll soon be looking for a way to keep them steady so you can study with ease. For smaller and larger porro prism designs, a wonderful (and inexpensive) alternative is the monopod. Sometimes referred to as a "Finn Stick", the monopod is a telescoping support with a mount on top that will allow you to directly attach your binoculars to it via a threaded hole in your binocular frame. This extremely portable unit won't stand on its own – but it's a great helping hand!
Binocular Astronomy – Binocular Tripod: Another great inexpensive alternative to holding larger binoculars steady is the simple photo tripod. Like the monopod, your binoculars should attach easily to this simple pan head via a threaded hole in the binocular body. The photo tripod now becomes a binocular tripod and the simple pan adjustments used to angle a camera now act as your hands – freeing you to enjoy the stars!
Binocular Astronomy – Parallel Tripod: For serious binocular astronomy use and large astronomical binoculars, the parallel tripod is highly recommended. It makes use of a counterbalance and the design allows you to move the binoculars freely in any direction – including viewer height. While they are more expensive, the parallel binocular tripod is a wonderful addition to astronomy binoculars for extended study times.
Binocular Astronomy – Getting Started With the Night Sky: Now that you have your equipment ready for binocular astronomy, it's time to get started with the night sky. If you are not already familiar with the constellations and what can be seen during any season of the year, it is highly recommended that you begin with a good planisphere. This simple rotary map will help you to identify constellations, major stars and often choice binocular targets as easily as setting the dial to a date and time. As you progress, you'll also want to add star charts of your own. But, before you buy an expensive set of charts, do a little homework. Make note of the objects you can see in your binoculars and what magnitude they are. It would be very disappointing to invest in star charts that listed too many objects you weren't able to see!
Binocular Astronomy – The Real View: Once you start practicing binocular astronomy, it's very important to understand that what you see will be far smaller than is often depicted in astronomy images. This isn't because the binoculars make it smaller (even with the same amount of magnification as a telescope), but because the field of view is so much wider. Using binoculars is like a panoramic view that's anywhere from 3 to 5 times larger than the average telescope eyepiece! For example, when looking at an open star cluster – such as shown here – a telescope will show a very bright, distinct pattern of stars. While binoculars will also reveal it, the field will be much wider and the object appear much smaller.
Do not be discouraged when practicing binocular astronomy if you think you can't find things. Chances are, you're probably looking right at them and not even noticing! Even exceptionally large objects, like a big globular cluster can be confusing when reduced. A telescope with its fixed and small field of view centers it very precisely – while binoculars (especially unsteady ones) may make it hard to determine smaller deep sky objects from the background stars. Take a look at this image for example… If this was one of the biggest and brightest globular clusters as seen in a telescope on the left and binoulars on the right, can you imagine how difficult it would be to spot a small and faint one? Your binoculars will reveal it – but your eye must comprehend it.
Like any form of astronomy, binocular astronomy takes patience, practice and persistence. It won't be long until you know your way around the sky and understand what you are looking for and what you can expect to see. Once you have that down? You'll spend a lifetime enjoying!
Filed under: Astronomy
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