Photography Calculators
Milky Way Exposure Calculator
https://www.photosizing.com/calculators/milky-way-exposure/
Estimate only — not a light meter, a shooting prescription or a studio plot. Confirm on a test shot.
Milky Way Exposure Calculator
Untracked Milky Way: shutter from the 500 rule, lens wide, ISO high enough that the histogram leaves the left wall. Suggested ISO scales from a common starting point — 20 s, f/2.8, ISO 3200 — so a faster lens or a longer 500-rule shutter pulls ISO down. Light pollution and moon will still toast the sky; take a test shot and read the histogram, not the LCD.
Inputs
Results
- 500-rule shutter
- 35.71s
- Suggested ISO
- 1,792
- EV at your ISO
- -7.19
Scaled from 20 s, f/2.8, ISO 3200. Not rounded to camera ISO steps.
Recommended gear
Fast astro lens
A 14 mm f/2.8 (or faster) is the untracked Milky Way default. Slow kit zooms push suggested ISO into mush.
Typical range: $400–$1,500
Star tracker
If 500-rule times are short on your focal length, tracking beats ISO 12800.
Typical range: $250–$600
Fast wide prime
A 24 mm f/1.4 or 20 mm f/1.8 is the next-best untracked option if you do not want a 14 mm.
Typical range: $200–$800
Calculation method
Shutter comes from the 500 rule: 500 divided by crop times focal length. Suggested ISO starts from a working dark-sky trio — 20 seconds, f/2.8, ISO 3200 — and scales with the square of 2.8 over your f-number and with 20 over your shutter, so a faster lens or a longer shutter pulls ISO down. Night EV is log2 of N²/t minus log2 of ISO/100 at the ISO you typed, not the suggested one.
White balance
Set a fixed Kelvin (around 3800–4800) or daylight and correct in RAW. Auto WB on the Milky Way is a lottery.
Focus
Infinity marks lie. Magnified live view on a bright star, then tape the ring. Recheck when the temperature drops.
Frequently asked questions
Why is suggested ISO not a camera step?
It is a continuous scale. Set the nearest native ISO (2500/3200/4000). Dual-gain bodies often prefer 500 or 800 as a floor — do not go below that just because the formula said 200.
Foreground too dark?
Blend a longer, lower-ISO foreground frame. Do not lengthen the sky shutter past the 500/NPF limit or the stars dash.
Bortle 8 backyard?
Skyfog will fill the histogram before the core does. Lower ISO, shorter total integration, or drive darker. This formula assumes a dark sky.
More in this topic
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500 Rule Calculator
Estimate the longest untracked shutter for stars with the 500, 300 and 200 rules from focal length and crop factor.
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Lunar Eclipse Exposure Calculator
Starting shutter for lunar eclipse phases from ISO and aperture: penumbral, partial, bright total umbra and dark Danjon totality.
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NPF Rule Calculator
Get a pixel-aware untracked star shutter from focal length, aperture, pixel pitch and an accuracy factor — tighter than the 500 rule on high-MP bodies.
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Star Trail Stacking Calculator
Work out stack length, sky-trail arc from Earth’s rotation and a 30 fps video duration from total minutes, interval and declination.