Hover over any point on the graph to see exact calculations for magnification, TFOV, field stop, and exit pupil.
Use the Advanced Settings panel to adjust axes and contour spacing.
When choosing eyepieces, aim for:
Exit pupil between ~0.5 mm (planetary) and 7 mm (wide-field). For suburban viewing, 2mm to 4mm offers a balance of obejct brightness and contrast without excess light pollution skyglow.
TFOV should be appropriate for the object you wish to frame, e.g. 1º to 2º for the Orion Nebula.
People often space eyepiece focal lengths by a factor of ~1.4x when building sets.
Example workflow to select an eyepiece:
Figure out an appropriate TFOV for your object (e.g., 1.5º for Orion).
Follow the contour line for your desired TFOV to choose an AFOV that suits your preferences. Then, check that the required barrel size for this TFOV fits your telescope’s focuser (indicated by the plot shading).
Look at the corresponding eyepiece focal length and check that it falls within your desired exit pupil size range.
Reverse the above workflow to evaluate which eyepieces work best for a given telescope.