Tuesday, May 12th, 2009 at
10:12 pm
Ann Marier asked:
The difference between a telescope and telescope binoculars is one eye. With a telescope you peer through the lens with one eye and with telescope binoculars you use them both. Additionally, telescope binoculars are similar to traditional binoculars, only with a much longer focal length.
It has been said that a person can see more in the sky with a good pair of binoculars than with a cheap telescope, and telescope binoculars are designed with star gazing in mind with wider aperture opening to allow more light into the lenses, offering a brighter view of the viewing subject. There are many binoculars on the market which can serve as telescope binoculars with the right focal length and magnification power, along with a reasonably wide lens opening.
Porro prism binoculars are better suited for night time gazing as they absorb less light through the prism path as do roof prism binoculars and will render a much brighter image when used as telescope binoculars in the typically low light conditions of nighttime viewing. However, upgrading optical quality and lens coatings are rapidly allowing the manufacturing of roof prism binoculars to meet the quality of porro prism units and they are gaining in popularity despite the higher cost.
Mount Telescope Binoculars For Stability
When using traditional binoculars as telescope binoculars it is best to have a unit with the capability to mount to a stable object such as a tripod or wooden deck to allow for better stability as well as in keeping them pointed in the same direction. Much like a telescope, they can be used to spot smaller objects in the sky, but can quickly lose sight of the object if moved and you will have to start the search all over again.
When looking for binoculars to double as telescope binoculars the numbers are important to know and understand. Binoculars are usually listed with two numbers, for example 10 X 50. This would indicate a magnification factor of 10, meaning the object will appear to be 10 times larger than the original and the diameter of the objective lens, in this case 50, determines the light gathering capability of the lens. While an objective measure of 30 is good for daytime use, a 50 would provide typically good views at night.
To be effective as telescope binoculars, a magnification of 100 with an objective opening of 70 or more would be preferred. Remember that the longer the magnification and lens opening the more the unit is subject to shake when being held in the hands. A tripod or mount will reduce this and is virtually necessary with longer lenses.
Tuesday, January 13th, 2009 at
1:41 am
Aidan James asked:
If you like to look to the heavens even just occasionally get yourself some decent binoculars and indulge in a little binocular astronomy. Think about it, binoculars are inexpensive, highly portable and require no complicated setting up procedure so are ideal for casual astronomy.
Binoculars allow excellent moon views, and great viewing of star fields, comets and even deep sky objects. They are especially useful for beginners as unlike astronomy telescopes they keep the view the the right way up, making it really easy to navigate the skies. With a little practice you can pick out several of the planets and even the larger moons orbiting Jupiter. Clusters like Pleiades look great because the binoculars wide field of view lets you have more of the cluster in view at one time than a telescope would.
So how to choose which ones? Binoculars have two specifications marked on the body of the binocular in the form of 7x 50, where the first number represents the magnification (in this case 7 times) and the second the aperture in millimeters (50mm in this case). When it comes to selecting the right binoculars for astronomy, aperture is the most important feature to think about. The bigger the aperture the more light is captured so the brighter and clearer the image will be. For astronomy use you will need at least 40mm aperture and preferably larger.
You will need a magnification factor of at least 7, maybe up to 10 if you have a steady hand. Any higher than about 10 times magnification and you will need to mount your binoculars on a tripod as the hand shake effect makes it difficult to get a sharp image.
There are giant binoculars available with higher magnifications and apertures which are designed for astronomy use but you will certainly need a sturdy tripod or mount to use them. These can offer excellent viewing up to about 25 times magnification with 100mm apertures.
This brings us to another point, a specification known as the ‘exit pupil’. This specification refers to the diameter of the shaft of light that exits the eyepieces and into your eyes. You can easily calculate it by dividing the aperture by the magnification so that 7 x 50 binocular has an exit pupil of just over 7mm. Capturing as much of that as possible is good as it means all the available light is getting to where you want it, i.e.your eye. If you are still in your twenties you can probably use all of that 7mm exit pupil mentioned above as your pupils will dilate to about that size in very dark conditions, however as you get older your pupil does not dilate more than about 4 to 5 mm so large exit pupils are wasted (though it starts to make those 25x 100’s look good!).
You might notice another specification marked on the binocular, the field of view (FOV), it refers to the apparent side to side view as you look through the binoculars. It will be expressed as an angle in degrees or a measure such as 340 feet at 1000 yards. For astronomy use we can generally ignore that factor, it really does not matter a great deal at the distances we’ll be viewing at.
So now you have the basics why not get yourself some binoculars and indulge in a little casual astronomy, you’ll be rewarded with some wonderful sights!
