What is the reciprocal rule?

It's a guideline that the slowest hand-held shutter speed for a sharp photo is roughly one over the focal length in seconds. At 50 mm on full-frame that's about 1/50 s; at 200 mm it's about 1/200 s, because longer lenses magnify shake more.

Why does sensor crop change the result?

Crop sensors magnify the field of view, which also magnifies any camera shake. The rule uses the 35mm-equivalent focal length, so a 50 mm lens on an APS-C body behaves like a 75–80 mm lens and needs a faster shutter than 1/50 s.

What does the strict (1/2×focal) option do?

High-resolution sensors resolve fine detail, so they reveal shake the classic rule would miss. The strict variant doubles the required shutter speed (one over twice the focal length) for a safer margin on demanding cameras.

How does image stabilisation change things?

Each stop of stabilisation lets you halve the shutter speed while keeping the same sharpness. Four stops of IBIS plus lens IS, for example, turns a 1/50 s limit into roughly 1/3 s — though real-world gains are often a stop or two less than rated.

Does this account for a moving subject?

No. The reciprocal rule only addresses blur from your own hand movement. A walking person, sports or wildlife will blur at these speeds regardless of stabilisation; freeze subject motion with a much faster shutter, often 1/500 s or higher.

What is the Camera Motion Blur & Shutter Speed Threshold Calculator?

Apply the reciprocal rule and its sensor-crop correction to find the minimum hand-held shutter speed for sharp photos at any focal length. Adjusts for APS-C, Micro Four Thirds and 1-inch crops and adds back stops for IBIS and lens stabilisation. It runs free in your browser on Gera Tools, with nothing uploaded.

Camera Motion Blur & Shutter Speed Threshold Calculator

Name: Camera Motion Blur & Shutter Speed Threshold Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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A sharp hand-held photo depends on a shutter fast enough to outrun your own movement. The classic reciprocal rule gives that threshold from focal length — this tool refines it for your sensor size and stabilisation so you know the slowest shutter you can safely use.

How it works

The rule starts from the focal length, but on anything other than full-frame you must use the 35mm-equivalent focal length, because crop sensors magnify shake along with the image:

effective_focal = focal_length × crop_factor
slowest_shutter = 1 / effective_focal      (seconds)

A 50 mm lens on an APS-C body (1.5× crop) behaves like 75 mm, so the limit tightens from 1/50 s to about 1/75 s.

Two adjustments refine this:

Strict / high-resolution mode doubles the requirement (1 / (2 × effective_focal)) because high-megapixel sensors reveal shake the original rule tolerated.
Stabilisation buys back time. Each stop lets you halve the shutter speed, so the usable shutter time is multiplied by 2^stops. Four stops turns a 1/60 s limit into roughly 1/4 s.

Practical guidance for hand-held shooting

Interpreting the result

The output is the slowest you can safely go, not a target shutter speed. Always err faster when in doubt — at worst you lose a stop of exposure that you can recover by raising ISO; a blurred shot is unrecoverable.

Stabilisation: expect less than the spec

Manufacturers rate IBIS and lens IS under ideal, controlled conditions. In real shooting — walking, breathing, excitement — you realistically get one to two stops less than the headline figure. If your camera claims five stops, plan on three to four for critical shots. The tool lets you dial this back manually by entering a conservative stop count.

High-resolution sensors and the strict mode

If you shoot a 45+ megapixel sensor, the classic reciprocal rule is too permissive. Those sensors resolve the slight softening from camera motion that older cameras simply could not capture. Use strict mode (1 / (2 × effective focal length)) for demanding work on high-resolution bodies.

When nothing replaces a tripod

Beyond roughly 1/15 s, even rated IBIS becomes unreliable for most shooters. Long exposures for landscape, architecture, macro, or astrophotography need a tripod. The tool tells you the limit so you know when you have crossed from hand-holdable into tripod territory.

Tips for pushing the limit

Exhale slowly and press the shutter at the natural pause between breaths.
Brace elbows against your chest or a solid surface.
Shoot a burst of three to five frames and keep the sharpest — camera motion varies shot to shot.
Mirror lock-up or electronic shutter eliminates mirror-slap vibration on DSLR bodies at intermediate speeds.
Raise ISO to use a faster shutter rather than fighting shake at the limit.