Exploring the Range of Telescope Vision: Elementary Concepts Explained
In the realm of astronomy, the field of view (FOV) is a crucial aspect that determines what you can observe through a telescope. This article aims to explain the concept of the field of view, focusing on the true field of view (TFOV) and how it can be calculated.
Calculating the True Field of View
The true field of view is the angular width of sky visible through a telescope's eyepiece. To calculate the TFOV, you first need to know the apparent field of view (AFOV) of the eyepiece and the magnification provided by the telescope-eyepiece combination.
The AFOV is a characteristic of the eyepiece, often provided by the manufacturer. It represents the number of degrees of sky the eyepiece would show if held directly up to the eye without a telescope.
Magnification depends on both the telescope and eyepiece focal lengths. It is found by dividing the telescope's focal length by the eyepiece's focal length.
With these values in hand, you can calculate the TFOV using the following formula:
[ \text{TFOV} = \frac{\text{AFOV} \times \text{Eyepiece Focal Length}}{\text{Telescope Focal Length}} ]
For example, if a telescope has a focal length of 1200 mm, the eyepiece focal length is 15 mm, and the eyepiece's apparent field of view is 70°, then:
- Magnification = ( \frac{1200}{15} = 80 )
- True field of view = ( \frac{70^\circ}{80} = 0.875^\circ ), approximately 0.9 degrees.
Key Points
- A larger field of view can provide more reference points for precise focusing, especially for objects that aren't sharply defined.
- A larger field of view can enhance the observing experience by providing a sense of depth and context.
- When set to a focal length of 24mm, the zoom eyepiece has an inherent apparent field of view of 60 degrees, resulting in a TFOV of about 2.2 degrees with a 650mm NexStar 130SLT.
- When set to a focal length of 8 mm, the zoom eyepiece has an inherent apparent field of view of 40 degrees, resulting in a TFOV of 0.49 degrees with a 650mm NexStar 130SLT.
- Changing the eyepiece on a telescope changes the magnification and the field of view.
- The field of view in astronomy refers to how much of the sky can be seen through a telescope's eyepiece.
- The TFOV is not always specified on an eyepiece and may need to be looked up online.
- Calculating the field of view of a telescope is a two-step process.
Navigating the Cosmos
Understanding the field of view can help you navigate the cosmos more effectively. With a larger field of view, you can easily match what you see in your telescope with star charts, even without a computerized GoTo telescope.
[1] This is a standard and widely accepted method for computing the true field of view in amateur and professional astronomy contexts.
- In astronomy, the field of view (FOV) is an essential factor that determines what can be observed through a telescope, particularly the true field of view (TFOV).
- To calculate the TFOV, one must first know the apparent field of view (AFOV) of the eyepiece, the eyepiece's focal length, and the telescope's focal length, along with the magnification provided by the telescope-eyepiece combination.
- The AFOV is a characteristic of the eyepiece, often provided by the manufacturer, representing the number of degrees of sky the eyepiece would show if held directly up to the eye without a telescope.
- Magnification is determined by the focal lengths of the telescope and eyepiece, and it is found by dividing the telescope's focal length by the eyepiece's focal length.
- With the calculated values, the TFOV can be determined using the formula: TFOV = (AFOV × Eyepiece Focal Length) / Telescope Focal Length.
- A larger field of view in astronomy can provide more reference points for precise focusing, enhance the observing experience by offering a sense of depth and context, and enable more effective navigation of the cosmos.
