TRG – Telescope Review Guide

My last article reviewed my second five most amazing sights in the night sky. This article will conclude with the Top 5!

5. The Andromeda Galaxy

The Andromeda Galaxy

The Andromeda Galaxy is a sister galaxy to our own Milky Way Galaxy. The light you see coming from it took 2.5 MILLION years to get here! It’s one of the most distant object most folks can see with the naked eye. Another reason it makes such a good target for binoculars is that it is orbited by 14 dwarf galaxies so there’s a lot to look at in the Andromeda Galaxy.

4. The Pleiades

The Pleiades

The Pleiades is a small star cluster that is also known as the Seven Sisters, probably because it looks like seven stars to the unaided eye. Train your binoculars on them though, and you can easily see many, many more than seven stars! It is indeed a sight worth seeing.

3. The Lagoon Nebula

The Lagoon Nebula

Nebulas are  star nurseries, places where gas is condensing under the force of gravity to form stars. The Lagoon Nebula is one of the most amazing nebulas visible from Earth. Look for it during summer in the constellation Sagittarius.

2. The Orion Nebula

The Orion Nebula

The Orion Nebula is located in the Hunter’s Sword of the Orion constellation. It is only 1270 light-years from Earth making it our nearest nebula.

1. The Milky Way Galaxy

The Milky Way Galaxy

Yes, our own home is so big that we can actually see part of the spiral arm where our own Earth is located! May be tough to spot behind city lights but get out away from them and the Milky Way is a visual treat not to be missed nor soon forgotten.

Bonus Sight

There is one other reason many amateur astronomers get into the field and use binoculars as their observation tool of choice – COMETS! Yes, astronomy is one of the view sciences where amateurs can make significant contributions and where amateur astronomers really excel is finding new comets. Many new comets are discovered by amateur astronomers and many of those discoveries are made using binoculars. So get your observation binoculars and get out away from city lights and start studying the night sky. Who knows? The next comet you see may be named for you!

So now you have a brand spanking new pair of Bushnell or Zhumell binoculars. Now what? Just what can you expect to see with them? You’d be surprised! What follows is sights 10-6 of my Top 10 list of things to see.

10. Meteors and Satellites

Find someplace where you have an unobstructed view of the sky. Try to pick a night with a new or crescent moon. Lay on a chaise lounge or even the ground. Be comfortable! Scan the sky with your binoculars. Before too long you should be rewarded by the flash of a shooting star! Most months have at least a minor meteor shower. April has the Lyrids which, as I pointed out in me last article, could put on a good show this year since the moon will be crescent during the peak of the shower.

Satellites are perhaps even more fun to view with your binocular than meteors since they don’t flash across the sky in an instant as meteors do. I will never forget the first time I saw the International Space Station fly over, Space Shuttle attached! Sure I could see it with my unaided eye but when I trained my Bushnell on them, I swear I could count the rivets! Simply breathtaking. Satellite hunting doesn’t have to be a hit or miss proposition either. Sebastian Stoff has a wonderful cardware program called Orbitron that will tell you when you’ll have a satellite viewable from your location.

9. The Beehive Cluster

The Beehive Cluster

The Beehive Cluster is an open star cluster found in the constellation Cancer. It should be on your list of must sees because it was one of the first things Galileo viewed with his telescope.

8. The Double Cluster

The Double Cluster is two clusters located close together. Located in the constellation Perseus, the Double Cluster makes an attractive target because it’s fairly large and telescopes have a hard time imaging both clusters at once. With your binoculars, you won’t have any trouble seeing both clusters!

7. Jupiter

Jupiter and the Galilean moons as you might see them with your binoculars

Sure, your friend with the telescope might be momentarily miffed at your ability to simultaneously image both clusters of the Double Cluster but he will soon turn his ’scope to Jupiter and challenge you to beat him. Of course, you probably won’t be able to but you will be able to reproduce Galileo’s efforts and watch the four largest moons of Jupiter, the so-called Galilean moon’s, in their nightly waltz around that gas giant!

6. The Moon

The Moon

Sure you can see the Moon, and plenty of it, without any aids at all. You haven’t really seen it though, until you’ve seen it through binoculars! Don’t try to view when the Moon is full, or nearly full, as the brightness will wash out the fine details and may be too bright to be comfortable for your eyes. Instead, view when the Moon is half or smaller. The shadows will reveal mountains and valleys like you’ve never dreamed! Look at the Sea of Tranquillity and imagine Neal Armstrong and Buzz Aldrin walking across that dusty surface. Has it really been 40 years since that amazing feat?

 Check back soon for my Top 5 list of things to see with your Bushnell or Zhumell binoculars!

What is in the night sky during April? The Moon, planets and even a meteor shower are on tap this month.
The Moon is especially noteworthy this month. It passes near all five of the naked-eye planets — Mercury, Venus, Mars, Jupiter, and Saturn plus as well as the stars Regulus and Antares. On the 22nd it will eclipse Venus as seen from most of the continental United States. 

Regulus, the brightest star of Leo, stands a little to the left or upper left of the Moon at nightfall on the 5th. The planet Saturn is below them.

Saturn aligns quite close to the Moon on the evening of the 6th, with Regulus above them.

Moon and Saturn by spaceritual

Antares, the brightest star of Scorpius, is close to the Moon on the 12th. It is close to the Moon’s lower left as they rise after midnight, and even closer at first light. As seen from Hawaii, the Moon will briefly eclipse Antares on the morning of the 13th.

 Jupiter stands a little to the lower left of the Moon at first light on the 18th. They are low in the southeast.

 The Lyrid meteor shower is at its best on the night of the 21st, especially with the Moon appearing as a thin crescent.

The Moon, Venus, and Mars congregate low in the east the morning of the 22nd. The Moon will eclipse Venus, briefly hiding the planet from view.

The Moon, the Pleiades, and the planet Mercury align low in the west-northwest as night falls on the 26th. The Pleiades star cluster is a little below the Moon, with Mercury about the same distance below the Pleiades. Mercury looks like a fairly bright star. Binoculars will enhance the view.

In my last article I discussed the various prism systems one could expect to find in binoculars. Now I’ll talk about lenses and lens coatings and how they affect the viewing experience.

Chromatic aberration is caused because light of different colors does not bend the same amount when passing between mediums of differing refractive indices such as glass and air.

This prism shows how different wavelengths of light is bent in differing amounts as it passes from air to glass and back to air again.

Blue light, for example, will not focus to the same plane as red light. The effect can create a ring of color around sources of light, and results in a general blurriness to the image. Chromatic aberration is minimised by using an achromatic doublet, or achromat, in which two materials, often crown and flint glass, with differing refractive indices are bonded together to form a single lens. While this reduces the amount of chromatic aberration over a certain range of wavelengths,  it does not produce perfect correction.
This problem can be reduced in several ways. One method is to apply a thin film to the eyepiece element that corrects. The more traditional approach is to eliminate the aberration by using multiple elements of different types of glass and curvature.
An apochromat is a lens or lens system which has even better correction of chromatic aberration, combined with improved correction of spherical aberration. Apochromatic lenses are designed to bring three wavelengths, typically red, green, and blue, into focus in the same plane. Apochromats are much more expensive than achromats.

Antireflection lens coatings reduce the amount of light reflecting off of the lens and allow more light to pass through. Without coatings, up to 50% of the light entering the binoculars can be lost to reflections because of the many glass surfaces within. The more expensive brands will have multiple coatings on all the lenses which will help to give the brightest and clearest images. The most used and least expensive coating is a single-layer of magnesium fluoride but there are also modern broadband multicoatings. Magnesium fluoride reduces reflections from 5% to 1%. Modern lens coatings , such as zinc sulphide or titanium dioxide, consist of complex multi-layers and reflect only 0.25% or less to yield an image with maximum brightness and natural colours. To save money, some optics manufacturers coat only some of the air-to-glass surfaces. Common antireflection coatings often look somewhat bluish, since they reflect slightly more blue light than other visible wavelengths, though green and pink tinged coatings are also used. Some binoculars ruby coatings intended to reduce glare in bright light and improve the contrast between brown and green objects. You should avoid any binocular that uses these coatings because it will perform poorly for astronomical use.

Coating symbols:

Coated (C) – One or more surfaces are coated.
Fully-Coated (FC) – All air-to-glass surfaces are coated but plastic lenses may not be.
Multi-Coated (MC) – One or more surfaces are coated.
Fully Multi-Coated (FMC) – All air-to-glass surfaces are coated.

Binoculars come with two types of focusing mechanisms. Most people opt for the center-focus model, which uses a centrally mounted wheel to adjust both eyepieces at once. There is also a separate adjustment for the right eyepiece, which helps to correct for any difference in near or farsightedness between your eyes.
The second focusing system uses individually focused eyepieces and has no centrally located focusing mechanism. Even though focusing is slower compared to the previous model, binoculars that use individual focus tend to be more rugged and less prone to moisture infiltrations.

Hermetically sealed binoculars filled with dry gas, often nitrogen, will not be susceptible to clouding due to condensation at low temperatures; this will also help to prevent mildew, although air may leak in over a period of years if the binoculars are not properly maintained.

Because binoculars are basically two small telescopes mounted side by side, an error in collimation (optical and mechanical alignment) can lead to numerous problems including eyestrain and double-images. For most binoculars collimation problems are not immediately obvious when you first pick the instrument up and view through it. If after using the binoculars for several minutes your eyes feel uncomfortable as they compensate for the barrel misalignment, most probably the binoculars are out of collimation, which means that the two barrels don’t point in the same direction. This is a serious problem, and you shouldn’t buy those binoculars.

Keep your binoculars in their protective carrying case to prevent dust and grit getting into the mechanism. This can clog up the lubricants and make the controls grind which could eventually seize up. Also avoid knocking them because prisms are often mounted lightly and a bump can misalign one, causing double vision. For the best view keep the front and rear lens surfaces clean with optical cleaning fluid and a soft lint free cloth.

Now that you know everything there is to know about choosing binoculars, I’ll write some articles about just what exactly you can expect to see with the new binoculars that you’ll want to buy with your income tax refund!

In Part One, I pointed out that binoculars can be a viable alternative to telescopes for astronomical viewing. I touched on magnification and aperture as ways of distinguishing and choosing which binocular is right for you. In part two, I’ll talk about digital binoculars

Digital Binoculars

and go into more detail about how magnification and aperture plays into binocular selection.

Digital binoculars are gaining in populararity – these capture a digital image seen through the binoculars. Zoom binoculars have the ability to quickly and very efficiently zoom in on the object of interest, but the image quality is compromised in cheaper models. The extra workings and glass inside reduce the amount of light available, making them unsuitable for astronomy. Avoid binoculars that claim to be “focus-free”.  Also be beware of advertising jargon like “high-powered”. Increasing the magnification will decrease the brightness and field of view, which makes objects faint and fuzzy. A lower magnification will maximise the amount of light transferred.

The larger the aperture, the brighter the image will be; but the greater the size, the binoculars will weigh and cost more. For general astronomy use, choose binoculars with an aperture of 50mm. An observation binocular with a 60mm objective lens will still be fairly portable while an observation binocular with a 80 to 100mm + objective lens is far more suited for static use. The size of the objective lens and the power of magnification are the two major factors that determine the light transmission of the binocular. For example, 50mm (the diameter of the objective lens) divided by 10 (the power of magnification) gives a figure of 5, which is the diameter (mm) of the exit pupil and indicates the amount of light reaching the eye. In general the larger the exit pupil diameter the brighter the binocular will appear and the better the resolution will be, enhancing colour and contrast perception, especially in low light conditions. However, since the human eye pupil dilates on average from 2.5mm to 7mm depending on light conditions it follows that an exit pupil above 7 is not beneficial as the human eye cannot accommodate it.

Remember also that as we age our eye pupil does not dilate so much, so a large exit pupil of 7mm is not so important for a 50 year old person compared with a 25 year old. So a 4mm exit pupil on a 25×100 observation binocular will be more than satisfactory for most users in most conditions, whereas a 40×100 will only give 2.5mm exit pupil, drastically reducing the amount of light reaching the eye. A standard 7×50 pair will have a 7mm exit pupil, the average human eye pupil size at night.

Most binoculars are not suitable for use with eyeglasses. You have to put your eye close to the eyepiece, but the glasses prevent you from getting close enough. You can of course take your glasses off to use the binoculars, but this can be a nuisance. It is possible to buy special binoculars which can be used with glasses. Standard binoculars have eye relief ranging from only a few millimetres to 15 millimetres. Long eye relief (15 to 25 millimetres or more) is necessary for eyeglass wearers. A poorly designed optical system can force the observer to press his or her eye close to the eyepiece in order to see an unvignetted image, or alternatively may have an exit pupil larger than the observer’s pupil at a comfortable viewing position, resulting in loss of light and a dimmer image.

The eyepieces of binoculars are usually permanently mounted in the binoculars, causing them to have a pre-determined magnification and field of view. Usually binocular eyepieces have 3-4 elements with marginal correction for colour and edge sharpness. The correction on Siebert 6 element eyepieces are comparable to a Japanese made Meade 26mm Super Plossl. The eyepieces do not add colour correction or false colour.
Wide-angle binoculars have a field of view that is wider than average (60 or higher).

The Field of View is the size of an area that can be viewed using the binoculars.

Binoculars are often advertised with their field of view specified in one of two ways: angular field of view, and linear field of view. Angular field of view is typically specified in degrees, while linear field of view is a ratio of lengths. For example, a pair of binoculars with a 5.8 degree (angular) field of view might be advertised as having a (linear) field of view of 305 feet per 1000 yards or 102mm per meter. As long as the field of view (FOV) is less than about 10 degrees or so, the following approximation formulas allow one to convert between linear and angular field of view. Let A be the angular field of view in degrees. Let L be the linear field of view in feet per 1000 yards. Let M be the linear field of view in millimetres per meter. Then:

A = 0.0191 \times L
A = 0.0573 \times M
L = 52.4 \times A
M = 17.5 \times A

Generally, higher powered binoculars give you a smaller field-of-view and the opposite is true for lower powered binoculars. For astronomy, a wide field of view is desirable because if offers a more pleasant viewing experience, and you can see more of the sky at a better edge performance compared to a narrower field.

Come back for part three when I talk about the various prism systems employed by binoculars.

Telescopes aren’t the only viewing tool at the amateur astonomer’s disposal. In part one of a series, I’ll discuss how binoculars can be very useful for several reasons: they are relatively inexpensive, have a large field of view and show images right side up (which makes finding things in the sky easier), are easily portable and require little to no setup.

So, how do you choose a good pair of binoculars for amateur astronomy?

There are different ways of categorising binoculars. Usually, they are distinguished by their magnification and the size of the aperture. A combination of a small magnification and large lens produces a brighter view. A 7×50 pair, for example, gives a brighter image than a 10 x 50, but the image magnification is smaller. A standard 7 x 50 pair is considered one of the best all-round binoculars for practicality, performance and price. For high-powered observation, a magnification of 25x with a 100mm objective lens is recommended.

Observation binocular

Observation binoculars come with either straight or angled eyepieces. The benefit of the angled design, usually 45º, is the ease of use and comfort of viewing. The angled eyepiece model is much more user-friendly, allowing more flexibility for people of different heights to use the binoculars without the need to continually adjust the tripod. It is also of benefit when the binocular is trained on the night sky. The straight eyepiece design model will require a higher adjustment of the tripod for each user and this may make the tripod less stable.

If you are forced to go out to the country where you cannot fix your binoculars to something, then consider image stabilised binoculars. These are far more expensive but have other applications as well.
Stabilisation may be enabled or disabled by the user as required. Stabilisation will allow binoculars up to 20× to be hand-held. Major brands making image stabilised binoculars include are Canon, Nikon, and Bushnell.

When I continue with Part 2 of my Astronomical Binocular Review Guide, I’ll talk about various features to look for in a binocular, including digital binoculars.

Last of a series

Your telescope

No matter what telescope you select, choose one that will meet your precise needs and interests. The planets, the Moon, and close stars require high power, good contrast, and sharp resolution, and if these are the objects of your attention, a refractor or reflector would be a good choice. Because very faint objects like galaxies and nebulae need a large aperture, you should invest in a big reflector telescope to view these. An all-purpose midrange telescope should serve best, for example a 6″ to 8″ reflector or an 8″ Schmidt-Cassegrain.

Keep checking back. Future articles will delve into filters used to cope with light polluted skies, astrophotography, astronomy book and software reviews, astronomical binoculars, and reviews of specific telescope models.