Handholding a long lens always leaves you guessing how slow the shutter can go. Enter the focal length, the sensor crop factor and your stabilization stops, and the tool returns the equivalent focal length, the shutter speed that matches it, and the closest standard speed you can dial in that is equal to or faster than that limit.
Equivalent focal length is the focal length multiplied by the crop factor, and the baseline shutter speed is its reciprocal. Since doubling equals one stop, the stabilization stops become a power of two that multiplies the baseline. The standard value comes from the 1/3-stop scale most cameras use (30" to 1/8000 s, e.g. 1/30, 1/40, 1/50, 1/60), and a value slower than the safe limit is never chosen: if you need 1/38 s, you get 1/40 s, not 1/30 s. Dial markings are rounded names, so the comparison uses the true 1/3-stop value (2 to the power n/3): 0.3" is really about 0.315 s, so a 0.30 s limit gets 1/4 s rather than 0.3". Limits of 0.3 s or longer are shown as decimal seconds (e.g. 0.87 s), and the standard value uses camera markings such as 0.3", 0.5", 0.8", 1" or 1.3"; faster speeds stay as fractions like 1/40 s. The one-over-focal-length rule is a widely used convention, not an official standard. Current as of October 2026.
Hand shake varies with the person, the stance and the pixel count, so the result is no guarantee of a sharp frame. Exposure, aperture and ISO pairings, angle of view and the blur that comes from a moving subject are not covered. Treat the figures as a reference and check one frame magnified on location.
Frequently Asked Questions
No. It is a convention carried over from the film era, not a figure set by any body. Hand shake differs from person to person and shows up more on high resolution sensors, so a faster shutter is often needed in practice.
Camera makers publish it alongside the sensor format. Full frame takes a 1. Notation differs a little between products, so it is an input rather than a constant.
Printed ratings come from the maker's own test conditions and may not match the field. Entering a stop or two below the rating and comparing the results shows where your own limit sits.