Learn · Choosing
Field of view: why it matters more than megapixels
The field of view is the patch of sky one image covers. It depends on the focal length and the size of the sensor. A wide field fits big nebulae and the Andromeda Galaxy; a narrow one shows small galaxies and planetary nebulae larger. No single field of view is best for everything.
What field of view means
The field of view is measured in degrees across and up and down. For comparison: the full Moon is about half a degree wide. A smart telescope with a field of 2.5° × 1.4° fits about five full Moons side by side; one with 0.75° × 0.56° fits only one and a half.
Focal length, sensor and field
A longer focal length magnifies more and gives a smaller field. A larger sensor captures a larger part of the image and gives a wider field. The aperture (the diameter of the lens or mirror) does not change the field of view: it decides how much light you collect and how much fine detail is possible.
Matching the field to your targets
We call an object "fits well" when its longest side covers between 20% and 95% of the short side of the frame. Bigger than that and you need a mosaic; smaller and it is a small dot that you will crop. The examples below show the same objects in the widest and the narrowest frame we track.
- Wide fields (about 2° or more): the Andromeda Galaxy, the Pleiades, the North America and Heart nebulae, the Veil.
- Medium fields (about 1° to 1.5°): the Orion Nebula, the Lagoon, most bright galaxies such as M81 and M82.
- Narrow fields (below 1°): small galaxies, globular clusters and planetary nebulae such as the Ring and the Dumbbell.
The same objects in a wide and a narrow frame
Why megapixels matter less
More pixels on a small field can show finer detail, but only if the optics and the atmosphere allow it. With small apertures and ordinary seeing, the field of view does far more to shape your photos than the pixel count.
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