Mount Cuba Astronomical Observatory

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Link to 2016 Highlights Letter to Friends of MCAO

 

INTERESTING ASTRONOMICAL WEBSITES

Stellarium.org - free planetarium program

Astronomy.com - home page of Astronomy magazine

Skyandtelescope.com - home page of Sky and Telescope magazine

heavens-above.com - home page of satellite prediction web site

mountcuba.org Mt. Cuba observatory homepage

spaceweatherlive.com real-time sunspot images and aurora predictions

 

BUYING YOUR FIRST TELESCOPE

PART I

"A GOOD PAIR OF BINOCULARS!"

Yes - the best first telescope is a good pair of binoculars! The route to learning to appreciate what the skies have to offer starts with gaining knowledge of the constellations and where things are to be found; then getting a closer look with binoculars and what they can offer (objects like Comet Hale-Bopp need these!); finally comes a telescope and what more and different it has to offer. Each aspect of gaining knowledge of the heavens has its own strengths and limitations. Learning them will allow you, the observer. to use the proper tool for the observation you want to make.

So, when it comes to buying binoculars, what do you need to know? To sum it up:

  • large objective diameter
  • magnification no greater than 7-8
  • proper size exit pupil
  • good eye relief
  • fully multi-coated optics
  • BAK-4 Porro prisms
  • rugged design
  • maybe a couple of other goodies

Simple, right? Maybe not, so let's get into some details.

First of all you need as large an objective diameter as is feasible. Simply put, the larger the diameter, the more light can get into your eye (and the fainter the objects you can view). However, there is a fine interplay between the objective diameter, the magnification and the exit pupil.

Second, when it comes to magnification, usually 7-8X (power) is the most you can use and still hold your binoculars steady. Third, the exit pupil is the diameter of the light beam as it exits the eyepiece. You can calculate it by dividing the objective diameter by the magnification. For the younger set, 6-7 millimeters is about the size of your dark-adapted eye pupil. But, for older folks - beyond age 40 or so, this is too much and an exit pupil of about 5 is more appropriate.

So, for a younger person, with a magnification of 7X and an exit pupil of 7 mm., an objective diameter of 50 mm. is about right (50 mm. divided by 7 [the magnification] is a little more than a 7mm exit pupil. More than large enough).

But, for an older person, with a magnification of 7X and an exit pupil of 5 mm., an objective diameter of 35 mm. is about right.

In binocular jargon, the young person's instrument would be a 7x50. That is, 7X magnification and 50 mm objective diameter. While the older person's would be a 7x35 - or 7X magnification and 35 mm objective diameter.

Both the 7x50 and 7x35 are commonly available binocular sizes; so you should not lack choices. The 7x50 binocular also has the pseudonym of 'night glasses' because they were originally designed for that purpose. However, the 7x35 is the 'night glass' for the older!

Fourth, consider eye relief, the distance back from the eyepiece the image forms (at the exit pupil). If you wear glasses and want to keep them on while viewing, you need good eye relief (i.e. 20 mm. or more). This number is available from the manufacturer. But, it may be that you will have to find this out for yourself - by looking through the binoculars (with and without your glasses) to decide if it's suitable.

Fifth, the term, fully multi-coated, refers to the optical coating that should be on every air-to-glass surface. Every time light hits glass a small amount is reflected away. You don't want this. You want the light to pass through with a minimum of trouble. When a surface is coated, this reflection is minimized. With a multiple coatings system, it's minimized even more. When light has the many, many air to glass passages to make typical of binoculars, there are a lot of possibilities for light to be reflected everywhere but straight through like you want (and need!). So you can see why it's important for each surface to be coated. A quick way to judge this is to look at the objective lens surface with a light source behind you. For every white colored reflection you see, you have an uncoated surface.

Sixth, the prisms in your binoculars should be made from BAK-4 glass, the best glass. This is a must for good light transmission. They should also be the Porro prism design to give the widest field through your instrument at the lowest cost.

Seventh, you should consider the mechanical design of the binocular. There are three common types: Zeiss, American and straight through. The latter are more difficult to make with wide, unvignetted fields of view. They are generally more expensive and can probably be left off your list to consider, at least for starters.

The very common (most common?) Zeiss types are more vulnerable to dropping or mishandling than the American type. Most of the Japanese and German made binoculars are Zeiss type (a notable exception is Fujinon binoculars). If you can get the American design with the other parameters OK, you can expect a longer, trouble-free life of use. (And, a good pair of binoculars should last YOU a lifetime!).

Finally, some other things you might like are a tripod mount or rubber coated barrels. Both can make life easier. Also look at the guarantee. Does the manufacturer with a 30 day guarantee have the same faith in their product as one that has a life time guarantee?

All these things are not going to be found in $25 binoculars; but you don't need $1000 for a good pair either. Start your buying adventure by looking in catalogs and stores and seeing what's available. Look for what we've just discussed. Maybe you can look through various models at star parties and ask the owners how their particular model performs. If you can find a store with more than one model, look through all that are in your price range. Things you might consider are: How heavy are they? Will you be comfortable holding them after a few minutes? Is the image in focus from edge to edge or is it sharp in the center and blurry around the edges. Does the image have good contrast. And can I really tell the difference between the $250 model and the $500 pair.

The difference between cheap models and more expensive ones are obvious. But as the price gets higher the differences become less. Only you know if you can justify that $500 pair when the image through the $250 pair was almost as good. Price alone is not always an indication of a good image. If the image through a $500 pair isn't as good as the $250 pair, why spend the extra money?

Armed with some basic information you can be an informed buyer and avoid the pitfalls that you shouldn't have to fall into.

[Original by Terry Lisansky - N3JJB - 12/16/98. Additions by Emil Volcheck]

Naming Your Star

As many of you know, there are companies that advertise that folks can have a star named for themselves, friends, etc. Recently, there was a lot of publicity about the naming of a Delaware State Star - now called the "Delaware Diamond".

The companies indicate that your named star will be included in some sort of publication and registered with the US Copyright Office - adding an air of authenticity of the naming process. However there is NOTHING OFFICIAL about the naming, it is not sanctioned by the IAU which has the worldwide authority in the official star naming procedure.

Mount Cuba Astronomical Observatory gets calls asking for information on whom to contact to get a star named. In the past, we have given that information over the phone - with some words of reminder that the names are NOT official. I have been uncomfortable with this, so we will not be doing it in the future.

I contacted Brian Marsden at SAO and, through him, Johannes Andersen, who is the General Secretary of the IAU. The IAU WebPages on the subject can be found by clicking here. 

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Last revised: May 26, 2017