Plan your equipment

Astronomy tools

Turn the numbers on your telescope, eyepiece, or camera into clear observing choices—with every result explained simply.

Simple answers from your equipment

Observing calculators

Everything calculates on this device

Enter the numbers printed on your telescope, eyepiece or camera.

Each result includes a plain-language explanation, so you do not need to know the formulas first.

Telescope setup

Telescope focal length mmEyepiece focal length mmTelescope aperture mm

Your magnification40×

Practical magnification for many targets.

Approximate useful maximum: 260×

See before you observe

Eyepiece apparent field°Object to preview

True field1.5°Full Moon · 0.5°

This object fits inside the view with room around it.

Brightness and comfort

Exit pupil3.25 mm

Telescope focal ratiof/7.7

Bright view; good for nebulae and star clusters.

Uses the same telescope and eyepiece values from calculator 01.

Camera planning

Camera formatLens focal length mm

Safer starting point8.3 sLess visible trailing

Traditional 500 rule13.9 sBrighter, but trails may appear

Take a test photo and zoom in. Modern high-resolution cameras may need an even shorter exposure.

These are practical estimates, not absolute limits. The atmosphere, optical quality and the observer's eyesight can change the result.