The Field of View (FOV) refers to the extent of the observable sky that you can see through your telescope at any given moment. Think of it as looking through a window— the wider the FOV, the more of the sky you can observe.
FOV in Visual Observation
- Apparent FOV - Typically provided by the eyepiece manufacturer in degrees.
FOV in Astrophotography
Or you can easily estimate by:
- Unit conversion
1° (degree) = 60’ (arcminute) = 3600″ (arcsecond)
- Sensor Size - Typically refers to the diagonal measurement of a rectangular sensor, but you can also use the horizontal or vertical measurement to calculate the FOV. Below are common sensor sizes:
ㅤ | Horizontal | Vertical | Diagonal |
Medium Format | 44mm | 33mm | 55mm |
Full Frame | 36mm | 24mm | 43.3mm |
APS-C | 23.5mm | 15.6mm | 28.2mm |
Micro 4/3 | 17.3mm | 13mm | 21.6mm |
Planetary Camera sensor | 6~8mm | 4~6mm | 7~10mm |
Using FOV to Determine Focal Length
On the contrary, you can also use the desired FOV (based on the celestial object you want to observe) to determine the focal length of the telescope you want to use. (Refers to Apparent Size of Common Celestial Objects)
Or you can easily estimate by: