Free astrophotography tool

Astrophotography Field-of-View Calculator

Match a telescope and camera, check image scale and sampling, and preview how popular celestial targets may fit inside the sensor frame.

JavaScript must be enabled to use this calculator.

Optical train

Enter the telescope and any reducer or Barlow used during imaging.

Telescope focal length mm Native focal length before a reducer or Barlow

Aperture mm Used to calculate the effective focal ratio

Reducer / Barlow factor Multiply the telescope focal length by this factor

Typical seeing arcsec Optional estimate used for sampling guidance

Camera sensor

Use pixel specifications or physical sensor dimensions from the camera data sheet.

Resolution + pixel size Sensor size + resolution

Image width pixels

Image height pixels

Pixel size µm Unbinned physical pixel pitch

Binning Changes image scale and effective output resolution, not total FOV

Sensor size is calculated from pixel count × pixel size.

Framing target

Select an approximate angular size to preview framing or enter a custom target.

Target

Target width arcmin

Target height arcmin

Target rotation 0° Visual aid only; actual orientation depends on camera rotation and sky position

Calculated setup

Your imaging field

Field of view -- × -- -- × -- arcmin

Effective focal length --

Effective focal ratio --

Sensor size --

Image scale --

Diagonal FOV --

Effective resolution --

Approximate framing

Sensor preview

Landscape sensor

-- --

Calculating target fit

Enter your equipment details to see an approximate framing assessment.

Target outlines use approximate catalogue dimensions and are a planning aid, not a detailed sky chart. Bright outer nebulosity may extend beyond the stated size.

Sampling guidance

Seeing vs image scale

Enter a typical seeing estimate to compare it with the calculated image scale.

Image scale = 206.265 × pixel size ÷ focal length.

Understanding the results

Field of view tells you the area of sky recorded; image scale tells you how finely that field is sampled.

Field of view

A shorter effective focal length or larger sensor captures a wider section of sky. The calculator uses the exact angular formula rather than the small-angle approximation.

Image scale

Arcseconds per pixel depends on pixel pitch and effective focal length. Binning increases the effective pixel size and therefore the image scale.

Sampling

A common starting point is roughly two to three pixels across the atmospheric seeing disc. Guiding, focus, optics and processing also affect useful detail.

Mosaics

When a target exceeds the sensor field, the framing verdict estimates a simple rectangular mosaic with approximately 15% overlap between panels.

Results are planning estimates. Actual framing can vary with quoted focal length, reducer spacing, sensor crop, camera rotation, distortion and the visible extent of an object. No values are uploaded or stored by AstroClassifieds.