Free tool

Field of view calculator

See what your setup really frames. Each configuration's field is drawn on a real sky image, at exact scale.

Angle of the frame's top edge, measured from north through east. The tick on the edge marks the top.

M42 · Orion Nebula · Nebulae · Orion

Catalogued size : 65′ × 60′ (source : Wikipedia)

Images: Digitized Sky Survey II (Caltech/Palomar, AAO/ROE), via STScI and the CDS hips2fits service (Strasbourg). Positions: SIMBAD (CDS).

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Field
1.28° × 0.72°
Diagonal
1.47°
Image scale
2.39 ″/pixel

Tight framing: the faint outer parts will be cut

According to the catalogue, the target is about 39% larger than the field. To capture all of it: mosaic of 1 × 2 panels.

Catalogued sizes do not always include faint outer parts. With long exposures a nebula can extend beyond them.

How it is computed

  • The field comes from the focal length and the sensor size: field = 2 × arctan(sensor / (2 × focal length)). A reducer multiplies the focal length by its factor. For smart telescopes we use each maker's published field, cross-checked against focal length and sensor.
  • Image scale is 206.265 × pixel size (µm) / focal length (mm), in arcseconds per pixel. For smart telescopes this is the pixel of the delivered image, after any binning.
  • The sky image uses a gnomonic projection, the same as a sensor behind a telescope. North up, east left. Frames are drawn in that projection, so the scale is exact, even for wide fields.
  • Positions come from SIMBAD. Sizes come from the source shown under each target: NGC 2000.0, SIMBAD, or Wikipedia when it cites NED or SEDS.
  • The image is fetched live from the CDS servers in Strasbourg. Nothing is stored on this site. Allow a few seconds depending on the field size.

Not equipped yet?

The comparison covers the 13 smart telescopes on the market: field, sensor, filters, price.

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