Just as there are many types of birders and birds, there are many types of binoculars or "binos".   Here are a few of the basics on binoculars:

• Magnification:  This refers to the power of the binoculars.  A pair of 7x35 binos are magnified 7 times.  The lower the power, the wider an area you can see through your binoculars and the brighter the image. This is particularly important in low light situations such as dawn or dusk.  Higher powered binoculars are useful for distant birds in open landscapes with abundant light.

• Aperture:  This is the measurement of the lens furthest from your eye, or the "objective lens".  The objective lens pulls in light from your surroundings similar to a camera lens.  In a pair of 7x35mm binoculars, the aperture is 35mm.  A larger aperture can compensate for the loss of light associated with a higher power, the trade-off is greater cost and weight.

• Glasses:  If you wear glasses at all times, do not choose a pair of binoculars without testing them with your glasses.  Glasses increase the distance between the lens and your eye, changing the eye relief. 

• Focus:  Poorly focused binoculars or binoculars that are out of alignment can cause dizziness, eyestrain, or severe eye-ache.  To avoid this, be sure to calibrate your binoculars before you go birding or after anyone has used them.  Here's how:

1. Adjust the two halves of the binoculars so the eyepieces are the same distance apart as your eyes.

2.  Pick a distant fixed object to focus on.  

3.  Turn the center focus all the way to the right.

4.    Close your left eye and adjust the right eye piece (the secondary focus knob)  until the object is in focus for the right eye.  This feature equalizes the difference in strength of your eyes.  If your binoculars do not have a focus knob on the right eyepiece, look for this knob either in front of the center focus knob, or around the objective lens on the right.   For future reference, note exact location of this setting (+,-, or 0 on most binoculars). 

5.  Open your left eye and adjust the central focus knob until that distant object is clearly focused.

Have patience, this can be a very frustrating experience and may take many tries to get it right!    If you or a more experienced birder cannot focus your binoculars clearly, you may need to have them re-aligned.