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LensCalc
How much magnification can your scope actually use?
Magnification is free — just fit a shorter eyepiece — but resolution is not. Beyond roughly 2x the aperture in millimetres you are enlarging blur rather than revealing detail, so a 150mm scope tops out near 300x no matter what eyepiece you use.
Exit pupil is aperture divided by magnification, and it should stay under about 7mm or light spills past your iris and is wasted. That sets a practical low-power limit, which matters for wide-field views of large targets like nebulae.
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OpenLast updated: August 2026
Magnification
48x
What you entered
Magnification
1,200 mm / 25 mm= 48xFocal ratio
1,200 / 150= f/8Maximum useful magnification (2x aperture in mm)
150 x 2= 300xExit pupil
150 / 48= 3.125 mmResult
Magnification: 48x