ATRONOMY – TELECOPE & OPTIC (46) CALCULATOR
Star Chart Fov
A precise tool.
What is the Star Chart Fov & How does it work?
The true field of view (TFOV) of a telescope tells you how much of the sky you can see through a particular eyepiece. It is expressed in degrees and depends on both the telescope’s optics and the eyepiece’s design.
The apparent field of view (AFOV) is a property of the eyepiece that describes the angular width of the view as perceived by the eye, usually given in degrees. When combined with the magnification produced by the telescope‑eyepiece pair, the AFOV can be converted into a real sky coverage.
Using the relationship TFOV = (AFOV × F_e) / F_t, where F_e is the eyepiece focal length and F_t is the telescope focal length, astronomers can quickly estimate how much sky will fit into their view for any combination of equipment.
TFOV = \frac{AFOV \times F_e}{F_t}
TFOV = true field of view (°)
Parameters
Result
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Frequently Asked Questions
What is the difference between TFOV and AFOV?
TFOV is the actual sky area you see through your telescope, while AFOV is the angular width of the view as seen by your eye.
How do I calculate the magnification of my telescope-eyepiece pair?
Divide the focal length of your telescope by the focal length of your eyepiece to get the magnification.
Can I use this calculator for binoculars too?
Yes, you can use a similar approach to calculate the field of view for binoculars using their magnification and objective lens diameter.
What is the typical AFOV range for eyepieces?
Eyepiece AFOVs typically range from 40° to 100°, with higher numbers providing a wider view.
How does magnification affect TFOV?
Higher magnification reduces the TFOV because it narrows the area of sky you can see at once.
Can I use this calculator to plan my stargazing sessions?
Yes, understanding your telescope’s field of view helps in planning which celestial objects to observe and how long you might need to spend on them.
What is the impact of eyepiece design on AFOV?
Eyepiece designs like Plossl, Kellner, or Erfle can affect AFOV; Plossls are popular for their wide field and good eye relief.
Results are for informational purposes only and do not constitute professional advice.