Telescope magnification is actually a relationship between two independent optical systems – the telescope itself and the eyepiece you are using. To determine power, divide the focal length of the telescope (in mm) by the focal length of the eyepiece (in mm). By exchanging an eyepiece of one focal length for another, you can increase or decrease the power of the telescope. For example, a 25 mm eyepiece used on a 1250 mm focal-length telescope would yield a power of 50x (1250/25 = 50) and a 10 mm eyepiece used on the same instrument would yield a power of 125x (1250/10 = 125). Since eyepieces are interchangeable, a telescope can be used at a variety of powers.
There are practical limits of magnification for telescopes. These are determined by the laws of optics and the nature of the human eye. As a rule of thumb, the maximum usable power is equal to 50-60 times the aperture of the telescope (in inches) under ideal conditions. Powers higher than this usually shows a dim, lower contrast image. For example, the maximum power on a 127 mm telescope (5” aperture) is in the range 250x - 300x. As power increases, the sharpness and detail seen will be diminished. The higher powers are mainly used for lunar, planetary, and binary star observations.
Most of your observations will be done with lower powers (6 to 25 times the aperture of the telescope in inches). With these powers, the images will be much brighter and crisper, providing more enjoyment and satisfaction with the wider fields of view.
A good way to increase magnification is to use a Barlow lens. A Barlow lens rated at 2x can be used with your existing eyepiece and it will double the magnification of any existing eyepiece.
Showing posts with label Barlow. Show all posts
Showing posts with label Barlow. Show all posts
Saturday, 15 February 2014
How do I use eyepieces with my telescope?
Your eyepieces are the first accessories you should have and use with your telescope. Since they are interchangeable, a telescope can be used at a variety of powers.
Look through the eyepiece by placing your eye just behind it to take advantage of its eye relief, the spacing between the lens and your eye. This should be at least 15 mm for the best comfort, maybe more if you wear eyeglasses. You’ll lose field of view if you place your eye farther away and may even move your eye out of the beam of light from the eyepiece. Viewing too close to the eyepiece will prevent you from blinking and may also cause a black ring to appear around the field of view.
Now turn the focus knob of the telescope, first one way then the other until the object is in focus.
Always start with the lowest power eyepiece (i.e., the one with the highest number in millimeters printed on it). It is much easier to focus and has a wider field of view, making it easier to aim the telescope at a distant target.
As power increases, the sharpness and detail seen will be diminished. The higher powers are mainly used for lunar, planetary, and binary star observations.
Most of your observations will be done with lower powers. With these lower powers, the images will be much brighter and crisper, providing more enjoyment and satisfaction with the wider fields of view.
A good way to increase magnification is to use a Barlow lens. A Barlow lens rated at 2x can be used with your existing eyepiece and it will double the magnification of any existing eyepiece. Since longer-focal-length eyepieces generally have longer eye relief, using a Barlow to increase magnification will allow more comfortable high-power viewing.
A basic set of eyepieces would be 32 mm, 20mm (or 26mm), and 10mm (or 16mm), plus a Barlow (2x or 3x power).
Look through the eyepiece by placing your eye just behind it to take advantage of its eye relief, the spacing between the lens and your eye. This should be at least 15 mm for the best comfort, maybe more if you wear eyeglasses. You’ll lose field of view if you place your eye farther away and may even move your eye out of the beam of light from the eyepiece. Viewing too close to the eyepiece will prevent you from blinking and may also cause a black ring to appear around the field of view.
Now turn the focus knob of the telescope, first one way then the other until the object is in focus.
Always start with the lowest power eyepiece (i.e., the one with the highest number in millimeters printed on it). It is much easier to focus and has a wider field of view, making it easier to aim the telescope at a distant target.
As power increases, the sharpness and detail seen will be diminished. The higher powers are mainly used for lunar, planetary, and binary star observations.
Most of your observations will be done with lower powers. With these lower powers, the images will be much brighter and crisper, providing more enjoyment and satisfaction with the wider fields of view.
A good way to increase magnification is to use a Barlow lens. A Barlow lens rated at 2x can be used with your existing eyepiece and it will double the magnification of any existing eyepiece. Since longer-focal-length eyepieces generally have longer eye relief, using a Barlow to increase magnification will allow more comfortable high-power viewing.
A basic set of eyepieces would be 32 mm, 20mm (or 26mm), and 10mm (or 16mm), plus a Barlow (2x or 3x power).
Subscribe to:
Posts (Atom)