FOVMath

Astrophotography calculators

9 calculators for planning an imaging or observing session. Each runs in your browser, shows the formula it uses below the inputs and lists the sources for that formula. The camera and telescope pickers are filled from the specifications on the manufacturers' own pages; you can also type your own values.

Two numbers drive most decisions: how much sky the sensor covers (field of view) and how much sky each pixel covers (image scale). Start with the field of view calculator if you are choosing a target, and with the sampling calculator if you are matching a camera to a telescope.

Field of view and framing

  • Field of view

    Field of view of any camera on any telescope or lens, from sensor size and focal length, using the exact arctan formula. With presets from maker specs.

  • Target framing

    Check whether a galaxy or nebula fits your sensor, with catalogue sizes and position angles, a star-chart preview and the focal length for a chosen fill.

  • Mosaic planner

    Count mosaic panels for a nebula or galaxy from your sensor, focal length and overlap, with both camera orientations tried and a panel layout chart.

Resolution and sampling

  • Image scale

    Arcseconds per pixel from pixel size and focal length (206.265 × µm ÷ mm), with binning, reducer factors and the telescope's resolution limit.

  • Sampling and seeing

    Pixels across the star FWHM for your camera, telescope and seeing, with under- and over-sampling verdicts, binning options and the published rules of thumb.

  • Reducer and Barlow

    Effective focal length, focal ratio, image scale and field with a reducer or Barlow, from its nominal factor or from lens focal length and spacing.

Exposure and data

  • Untracked exposure (NPF)

    Longest untracked exposure before stars trail, by the 500 rule and by Michaud's NPF rule (simplified and complete), with trail length in pixels.

  • Session storage

    How many gigabytes a night of imaging produces: FITS frame size from resolution and bit depth, calibration frames, and 32-bit processing copies.

Visual observing

  • Eyepiece

    Magnification, exit pupil and true field for any telescope and eyepiece, from apparent field or field stop, with Barlow and your own pupil size.