Free planning tools · Check equipment compatibility

Pixel scale and sampling calculator

Compare two camera and telescope combinations against the seeing range you expect.

No account needed. Results update here as you change the inputs. Measurements stay in this tab unless you choose to share a link; shared links contain the inputs, including any location coordinates.

Your inputs

The starting values are examples. Replace them with your own measurements, prices or documented requirements.

What to have ready
  • Focal length and native pixel size for both setups.
  • The whole-number binning factor used for the recorded image.
  • A realistic seeing range for the session, not a forecast supplied by this page.
Measurements for Pixel scale and sampling calculator

Calculated from your inputs

Your plan

The example will calculate here when JavaScript is ready.

What to do next

    Calculation details

    Inputs used in this result

    Compare a change before committing

    Keep this plan, change the inputs and see the difference. The comparison stays in this tab.

    What does a camera or focal-length change do to image scale?

    Compare two setups against the same assumed seeing range rather than treating smaller pixels as an automatic upgrade. This pixel scale calculator shows the angular width of a pixel and how many recorded pixels span the entered seeing estimate.

    The useful result is a description of the trade-off, not a universal green or red rating. A shared comparison lets someone check the focal lengths, pixel sizes and binning assumptions before recommending a change.

    How to use this planner

    1. Enter both telescope and camera combinations.
    2. Keep the seeing range fixed while changing one equipment variable.
    3. Read the image scales and pixels across seeing, then check field of view and tracking too.

    The calculation

    Image scale = 206.265 × pixel size in µm × bin factor ÷ focal length in mm. Pixels across seeing FWHM = seeing in arcseconds ÷ image scale.

    A worked example

    3.76 µm pixels at 600 mm and 1× binning give 1.29 arcsec/pixel. A 2–3 arcsec seeing disc spans about 1.55–2.32 pixels.

    Example inputs are demonstrations. Replace them with your own measurements, prices or documented requirements.

    Assumptions and limits

    This uses a small-angle approximation and square pixels. Seeing is a user estimate, not a forecast. The range is descriptive, without a universal ideal or pass/fail ratio. Optics, focus, guiding, target and processing also matter. Binning may be software resampling rather than hardware charge summation.

    AAVSO CCD photometry guide

    Questions about this calculation

    Is the setup with more pixels across the seeing disc always better?

    No. More recorded samples are one characteristic, not a complete image-quality verdict. Optics, focus, tracking, signal and processing can change the practical result.

    Should I enter the camera pixel size after binning?

    Enter the native pixel size and let the separate bin factor apply it once. Confirm what your camera or software actually records; software resampling is not always equivalent to hardware binning.

    Put the result in context