Free astronomy tool

Telescope Magnification Calculator

Choose your telescope and eyepiece to see the magnification and how much sky fits in the view.

Choose a telescope
Set the eyepiece and Barlow
Compare the results

Select Base Telescope Model

Choose from vetted models or switch to custom specs:

Sky-WatcherChecked 2026-10-25

Sky-Watcher Classic 200P 8" Dobsonian

203mm (8") • 1200mm (f/5.9)

Sky-WatcherChecked 2026-09-11

Sky-Watcher Heritage 150 Tabletop Dobsonian

150mm (5.9") • 750mm (f/5)

CelestronChecked 2026-10-27

Celestron NexStar 6SE Schmidt-Cassegrain

150mm (5.9") • 1500mm (f/10)

CelestronChecked 2026-10-26

Celestron StarSense Explorer DX 102AZ Refractor

102mm (4") • 660mm (f/6.5)

CelestronChecked 2026-10-27

Celestron NexStar 8SE Schmidt-Cassegrain

203.2mm (8") • 2032mm (f/10)

Sky-WatcherChecked 2026-09-15

Sky-Watcher SkyMax 127 AZ-GTi

127mm (5") • 1500mm (f/11.8)

Eyepiece & Barlow Lens Configuration

Eyepiece Focal Length:10 mm

Barlow Auxiliary Lens:

A 2x Barlow effectively doubles the focal length of your scope (750mm → 1500mm), doubling magnification on any eyepiece.

Eyepiece Apparent Field (AFOV):

Factory Rig Insight for Sky-Watcher Heritage 150 Tabletop Dobsonian:

These accessories are optional starting points. Confirm barrel size, voltage, polarity, mount clearance, and resulting magnification for your exact telescope before buying.

Calculated Optical Physics

Total Magnification

150x

Max Ceiling: 300x•Exit Pupil: 1 mm

🪐 High Planetary Magnification

This is a high-power configuration. Visible detail depends on aperture, optical quality, collimation, target altitude, and atmospheric seeing.

True Field of View0.44°

(Full Moon = 0.5° wide)

Exit Pupil Size1 mm

Crisp comfort

Build Your Complete Stargazing Kit

Select Essential Accessories & City Upgrades

Check the accessories to include in your customized rig tally:

Estimated Setup Tier:Pricing pausedExact listings under verification

barlowVerification pending

Celestron Omni 2x Barlow Lens (1.25")

Useful only when the telescope, eyepiece, and atmospheric conditions support the resulting magnification.

Confirm the exact product listing and every interface against the telescope or camera manual.

✓ In My Rig

eyepieceVerification pending

SVBONY 6mm 66° Ultra Wide-Angle Eyepiece ("Goldline")

Choose focal length and barrel size from the telescope specifications; useful magnification and eye comfort vary.

Confirm the exact product listing and every interface against the telescope or camera manual.

+ Add

eyepieceVerification pending

Celestron 8mm–24mm Deluxe Zoom Eyepiece

Choose focal length and barrel size from the telescope specifications; useful magnification and eye comfort vary.

Confirm the exact product listing and every interface against the telescope or camera manual.

+ Add

filterVerification pending

Orion 1.25" 13% Transmission Moon Filter

Filter results depend on target, bandpass, aperture, and sky conditions. No filter improves every object.

Confirm the exact product listing and every interface against the telescope or camera manual.

✓ In My Rig

filterVerification pending

SVBONY 1.25" UHC (Ultra High Contrast) City Light Pollution Filter

Filter results depend on target, bandpass, aperture, and sky conditions. No filter improves every object.

Confirm the exact product listing and every interface against the telescope or camera manual.

+ Add

collimationVerification pending

SVBONY 1.25" Deluxe Laser Collimator with 7 Brightness Levels & 2" Adapter

The tool must fit squarely and should itself be checked for alignment before it is trusted.

Confirm the exact product listing and every interface against the telescope or camera manual.

+ Add

power comfortVerification pending

Celestron Vibration Suppression Damping Pads (Set of 3)

Check the exact voltage, polarity, connector, load, surface, and runtime requirements for the intended setup.

Confirm the exact product listing and every interface against the telescope or camera manual.

+ Add

power comfortVerification pending

TalentCell 12V 6000mAh Rechargeable Lithium Power Bank

Check the exact voltage, polarity, connector, load, surface, and runtime requirements for the intended setup.

Confirm the exact product listing and every interface against the telescope or camera manual.

+ Add

mount upgradeVerification pending

Celestron StarPointer Finderscope

Verify mounting shoe, thread, camera mount, clearance, and any required adapter before purchase.

Confirm the exact product listing and every interface against the telescope or camera manual.

+ Add

power comfortVerification pending

Celestron Night Vision Red LED Astronomy Flashlight

Check the exact voltage, polarity, connector, load, surface, and runtime requirements for the intended setup.

Confirm the exact product listing and every interface against the telescope or camera manual.

+ Add

eyepieceVerification pending

Celestron 1.25" Eyepiece and Filter Kit (14-Piece)

Choose focal length and barrel size from the telescope specifications; useful magnification and eye comfort vary.

Confirm the exact product listing and every interface against the telescope or camera manual.

+ Add

mount upgradeVerification pending

Celestron T-Ring for 35mm Canon EOS DSLR Cameras

Verify mounting shoe, thread, camera mount, clearance, and any required adapter before purchase.

Confirm the exact product listing and every interface against the telescope or camera manual.

+ Add

Try this example

A 1,000 mm telescope with a 10 mm eyepiece gives 100× without a Barlow. With a 60° apparent-field eyepiece, the estimated true field is 0.6°. If the telescope has a 100 mm aperture, the exit pupil is 1 mm.

How the tool works

Magnification is telescope focal length × Barlow factor ÷ eyepiece focal length. Exit pupil is aperture ÷ magnification. Approximate true field is eyepiece apparent field ÷ magnification. The displayed values are rounded.

True field is an approximation; an eyepiece field-stop measurement gives a more precise estimate. A calculated power does not guarantee sharp detail. Atmosphere, optical alignment, focus, and mount stability still matter.

Questions about this tool

How do I calculate telescope magnification?

Divide the telescope focal length by the eyepiece focal length, using the same units. A 1,000 mm telescope and 10 mm eyepiece give 100×. A nominal 2× Barlow changes that to about 200×.

What is exit pupil?

Exit pupil is the width of the light beam leaving the eyepiece. Divide telescope aperture by magnification to estimate it. Smaller exit pupils generally make extended objects look dimmer.

Will a higher magnification show more detail?

Only up to the limits set by the telescope, target, and air. If the image gets larger but softer, reduce power. The calculator’s upper guideline is a planning aid, not a performance promise.

Sources and method: Sky & Telescope magnification guide