Calculadora de Velocidade do Obturador
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
t_max = 500 / (focal × crop)
About this calculator
The Shutter Speed Calculator is a practical tool for photographers, especially in astrophotography. It calculates the maximum exposure time to avoid star trails using the 500 Rule, which depends on the lens focal length and camera crop factor. The formula is simple: 500 divided by the product of focal length and crop factor. The result is the maximum time in seconds before stars start to trail.
Additionally, the calculator converts aperture (f/) and shutter speed values to EV (Exposure Value), making it easy to compare different settings. EV is a logarithmic scale that combines aperture and time; for example, 1 second at f/1.0 equals EV 0. Higher values indicate more brightness. You can enter aperture and time to get the corresponding EV.
Use this calculator when planning night sky photos, Milky Way shots, or meteor showers. It's also helpful for adjusting exposure in low light conditions, such as interiors or night landscapes. Keep in mind that the 500 Rule is an approximation; for high resolution cameras, you may need to use 400 or 300 for sharper results.
Important considerations: the 500 Rule assumes you are using a wide angle lens. For telephoto lenses, the maximum time is very short, making tracking necessary. Also, crop factor varies: 1.0 for full frame, 1.5 for Nikon APS C, 1.6 for Canon APS C, 2.0 for Micro Four Thirds. Check your camera's crop factor for accurate results.
Frequently asked questions
What is the 500 Rule?
It is a formula to estimate the maximum exposure time in astrophotography to avoid star trails. Calculate 500 divided by the equivalent focal length (actual focal length times crop factor).
Why use 500 and not another number?
The number 500 is an empirical value that works well for medium resolution cameras. For high resolution cameras, such as 24 megapixels or more, 400 or 300 is recommended to avoid noticeable trails.
What is EV and how to interpret it?
EV (Exposure Value) is a scale representing the combination of aperture and shutter speed. EV 0 corresponds to 1 second at f/1.0. Higher values indicate more light; lower values less light.
Can I use the calculator for daytime photography?
Yes, the EV part is useful for any situation. But the 500 Rule is specific for night astrophotography to avoid star trails.
How do I find my camera's crop factor?
Check the manual or specifications online. Full frame has factor 1.0; APS C Nikon 1.5; Canon 1.6; Micro Four Thirds 2.0. Smartphone cameras usually have larger factors.