What is the NPF Rule in astrophotography?

The NPF Rule is a formula for calculating the maximum shutter speed before stars begin to trail in astrophotography. It's more accurate than the 500 Rule because it accounts for your camera's pixel pitch (sensor resolution) and lens aperture. The formula is: NPF = (35 × Aperture + 30 × Pixel Pitch) ÷ Focal Length.

How is NPF different from the 500 Rule?

The 500 Rule only considers focal length (500 ÷ focal length), while the NPF Rule also factors in your camera's sensor resolution and lens aperture. This makes NPF significantly more accurate, especially for modern high-megapixel cameras where the 500 Rule often results in star trails.

What is pixel pitch and why does it matter?

Pixel pitch is the distance between pixels on your camera sensor, measured in micrometers (μm). Cameras with smaller pixels (higher megapixels) have smaller pixel pitch and show star trailing more easily, requiring shorter shutter speeds. The NPF Rule accounts for this.

What shutter speed should I use for Milky Way photography?

Use the NPF Calculator to find your exact maximum shutter speed based on your camera and lens. Typically, for a 24mm lens at f/2.8 on a full-frame camera, you'll get around 10-15 seconds. Always use the 'Sharp' setting for critical work.

How do I find what stars are visible tonight?

Enter your location coordinates or use the "Use My Location" button. The viewer will show all stars currently above your horizon, sorted by altitude. Higher altitude means better viewing conditions.

What is the best time for stargazing?

The best time is during astronomical twilight or full night, when the sun is more than 18 degrees below the horizon. The viewer shows the current twilight phase to help you plan.

What does altitude mean in stargazing?

Altitude is the angle of an object above the horizon, measured in degrees. 0° is at the horizon, 90° is directly overhead (zenith). Objects higher than 30° are easier to observe with less atmospheric interference.

NPF CalculatorAstrophotography Tools

Night Sky Viewer

See what's visible in the sky tonight from your location. Find stars, constellations, and deep sky objects for your imaging session.

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Day

Sun altitude: 50° • Spring sky

Local Sidereal Time

23:42:58

⚠️ Not ideal for stargazing. Wait for astronomical twilight (sun below -18°) for best viewing.

Your Location

Latitude

Longitude

Min Altitude (°)

🌟 Spring Highlights

Whirlpool GalaxyLeo TripletVirgo ClusterLeoVirgoUrsa Major

Sky View

Stars

Deep Sky

Constellations

Visible Stars

Name	Altitude	Direction	Mag	Notes
Deneb Cygnus	56.6°	WNW (294°)	1.3	Summer Triangle star
Polaris Ursa Minor	40.5°	N (1°)	2.0	The North Star
Vega Lyra	32.9°	WNW (296°)	0.0	Summer Triangle star
Capella Auriga	31.5°	NE (54°)	0.1	The Goat Star
Altair Aquila	30°	WSW (255°)	0.8	Summer Triangle star
Aldebaran Taurus	23.2°	E (88°)	0.8	The Bull's eye
Fomalhaut Piscis Austrinus	19.6°	S (191°)	1.2	The Lonely One

How to Use the Night Sky Viewer

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1. Set Location

Use the "Use My Location" button or enter your coordinates manually. The sky changes dramatically based on your latitude.

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2. Check Visibility

Objects higher in altitude (closer to zenith) are better for observation as they pass through less atmosphere.

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3. Find Direction

Use the azimuth and cardinal direction to know where to point your telescope. N=0°, E=90°, S=180°, W=270°.

Stargazing Tips

Best Viewing Conditions

•Wait until astronomical twilight (sun below -18°)
•Objects above 30° altitude have less atmospheric distortion
•Check moon phase - new moon is best for deep sky
•Let your eyes dark-adapt for 20-30 minutes

Understanding the Sky Map

•Center = Zenith (directly overhead)
•Edge = Horizon (0° altitude)
•North is at top, East at right
•Brighter stars appear as larger dots

Plan your complete imaging session:

Session Planner•Moon Calendar•Dew Point•Polar Alignment•Bortle Scale