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.

NPF CalculatorAstrophotography Tools

Moon Phase Calendar

Plan your astrophotography sessions around the lunar cycle. Find the best dark sky nights for deep sky imaging.

🌕

Full Moon

100% illuminated

Tonight's Conditions

Best for lunar photography! Or capture moonlit landscapes.

Rating

★☆☆☆☆

Next New Moon

Thu, Dec 18

13 days away

Next Full Moon

Fri, Dec 5

1/5

for deep sky

Suggested Targets Tonight

Detailed lunar imagingLunar features and cratersMoonlit landscapesPlanet conjunctions with Moon

December 2025

8 great nights this month

Sun

Mon

Tue

Wed

Thu

Fri

Sat

Best Nights in December 2025

Great Nights

Good or Better

🌑

18, 19, 20, 21

🌕

3, 4, 5, 6, 7

Understanding Moon Phases for Astrophotography

Why Moon Phase Matters

The moon is the brightest object in the night sky after the sun. Even a crescent moon can significantly increase sky brightness, washing out faint nebulae and galaxies. Understanding the lunar cycle helps you maximize your imaging opportunities.

•New Moon (0-5%): Darkest skies, ideal for faint objects
•Crescent (5-25%): Good conditions, moon sets/rises early
•Quarter (25-50%): Plan around moonrise/set times
•Gibbous (50-95%): Focus on bright objects or lunar imaging
•Full Moon (95-100%): Best for lunar photography

Planning Tips

🌑 New Moon Window

The ~5 days centered on new moon offer the best deep sky conditions. Plan your most ambitious targets for these nights.

🌙 Working Around the Moon

During gibbous phases, check moonrise/moonset times. You can still image before moonrise or after moonset.

📸 Lunar Photography

Full moon isn't wasted time! Capture incredible lunar detail or try your hand at moonlit landscape astrophotography.

Frequently Asked Questions

What is the best moon phase for astrophotography?

The new moon phase (0-5% illumination) is ideal for deep sky astrophotography. During this time, the sky is darkest, allowing you to capture faint nebulae, galaxies, and the Milky Way with minimal light interference.

Can I do astrophotography during a full moon?

Yes, but you should focus on different subjects. During full moon, capture lunar surface details, moonlit landscapes, or bright planets. For deep sky objects, use narrowband filters or wait until the moon sets.

How many good astrophotography nights are there per month?

Typically 10-14 nights per month have moon illumination below 35%, which are considered good for deep sky astrophotography. About 5-7 nights have illumination below 15%, which are excellent conditions.

What targets should I photograph based on moon phase?

During new moon: faint nebulae, galaxies, Milky Way. First/last quarter: bright nebulae, star clusters. Full moon: lunar surface, planets, moonlit landscapes.

How accurate is this moon phase calculator?

Our calculator uses astronomical algorithms based on the synodic month (29.53 days) and is accurate to within a few percent for illumination values.

Combine with our other astrophotography tools:

NPF Calculator•FOV Calculator•Exposure Calculator•Star Trail Calculator•Bortle Scale Guide