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ASTRONOMY BINOCULARS
Choosing Binoculars

Aperture, Magnification and Exit Pupil

The aperture of binoculars is simply the diameter of the main large object lenses. Magnification always refers to the linear magnification. Thus binoculars with 8x magnification will show objects as 8 times taller, and 8 times wider, than as seen with the unaided eye.


    Examples: 7 x 50 binoculars have 7x magnifaction and 50mm aperture, 8 x 30 binoculars have 8 x magnifaction and 30mm aperture.

Perhaps the most important factor in choosing binoculars is the exit pupil. The bundle of light rays from a distant object enters the binoculars through the aperture, and emerges from the eyepiece as a smaller bundle of light rays, which enters the eye. The diameter of the light bundle emerging from the eyepiece is called the exit pupil of the binoculars. The exit pupil is easy to calculate - it is simply the aperture of the binoculars divided by the magnification;

    Examples: Exit pupil for 8 x 30 binoculars is 30/8 = 3.75mm
       Exit pupil for 7 x 50 binoculars is 50/7 = 7mm approx.

It is important that all the light from the object enters the eye, otherwise the view will be dimmer. So we want the pupil in your eye (the black "hole" in the centre of the eye) to be larger than the exit pupil of the binoculars.

Now, the size of the eye pupil varies with light conditions. In daylight, the eye pupil will be quite small, perhaps only 2mm diameter. So, in daylight, the large 50mm aperture of 7 x 50 binoculars is wasted, because only 2mm of the 7mm exit light bundle will enter the eye.

But under darker conditions, the eye pupil opens up (dilates), and in younger people (under about 30) the pupil can dilate to 7mm under really dim conditions. Then the 7 x 50 binoculars will come into their own, and the full benefit of the large aperture will be gained.

But it depends on your observing environment. If you observe from an urban location, light pollution will prevent the eye pupil from becoming fully dilated.

Unfortunately the capacity of the human eye deteriorates with age, so that by age about 50, most peoples eyes will expand to less than 6mm pupil size.

Recommended Binoculars

As a first pair of binoculars for astronomy, choose the 7 x 50 if you have little in the way of light pollution, and are aged under about 40. If one, or both of those conditions don't apply, then go for the 10 x 50. Binoculars of this size will double as binoculars for terrestrial use, (eg birdwatching etc) but for astronomy use, a tripod is desirable. It is amazing how much more detail can be seen if the binoculars are held rock-steady by a tripod. Various designs of tripod are available.




Celestron SkyMaster 8x56mm Binoculars
Price $309.95
Sale $209.95

Customer Score:4.5 Stars

Celestron SkyMaster 9x63mm Binoculars
Price $341.95
Sale $229.95

Customer Score:5.0 Stars

Celestron SkyMaster 20x80mm Center Focus Binoculars
Price $205.95
Sale $149.95

Customer Score:4.5 Stars

Celestron Cometron 12x70 Binoculars
Price $114.95
Sale $89.95

Customer Score:4.5 Stars

Celestron Cometron 7x50 Binoculars
Price $42.95
Sale $34.95

Customer Score:3.0 Stars

Celestron Cometron 12x70 Binocular with Tripod Kit
Price $133.90
Sale $119.98

Customer Score:5.0 Stars

Celestron SkyMaster 20x80 Binocular with Tripod Kit
Price $349.90
Sale $219.98

Customer Score:3.0 Stars

Canon 15x50mm IS Image Stabilized All Weather Binoculars
Price $2200.00
Sale $1499.98

Customer Score:4.5 Stars

Canon 18x50mm IS Image Stabilized All-Weather Binoculars
Price $2500.00
Sale $1599.98

Customer Score:4.5 Stars

Kowa Highlander 32x82mm Fluorite Binoculars
Price $5560.00
Sale $2999.00

Customer Score:5.0 Stars

Nikon 10x50mm Action Extreme ATB Binoculars
Price $179.95

Customer Score:4.5 Stars

Nikon 20x120mm Bino-Telescope
Price $9799.95

Nikon 18x70mm Astroluxe Binoculars
Price $1799.95

Nikon 10x70mm Astroluxe Binoculars
Price $1749.95

Pentax 20x60mm PCF WP II Binoculars
Price $239.00

Customer Score:4.0 Stars

Swarovski SLC 8x56mm B Binoculars
Price $1943.33
Sale $1799.00

Customer Score:5.0 Stars

Vixen 8x56mm Geoma ZCF Binoculars
Price $560.00
Sale $379.00

Vixen 7x50mm Geoma ZCF Binoculars
Price $490.00
Sale $349.00

Customer Score:5.0 Stars

Vixen Foresta 7x50mm CF Binoculars
Price $420.00
Sale $329.00

Vixen 10x50mm Ascot Super Wide Astronomy Binoculars
Price $250.00
Sale $169.00

Customer Score:4.5 Stars

Vixen BT81S-A Binocular Telescope
Price $2800.00
Sale $999.00

Zhumell 20x80mm SuperGiant Astronomical Binoculars
Price $199.00
Sale $119.98

Customer Score:4.5 Stars

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