Flash Guide Number
About Guide Number
What this tool does
Photography tools provide shutter speed charts, ISO noise guides, focal length comparisons, crop factor calculations, depth-of-field estimates, exposure compensation references, and megapixel-to-print-size tables.
Why use this tool
Photographers in the field need quick answers: What shutter speed freezes motion at this focal length? How large can I print from a 24MP sensor? What is the equivalent focal length on a crop sensor? These references save trial-and-error shots.
How it works
Exposure tools apply the reciprocal rule (minimum shutter speed = 1/focal length). Depth-of-field calculations use the thin-lens equation with circle-of-confusion diameter. Print-size tables divide sensor resolution by the target DPI.
Pro tip
The reciprocal rule gives the slowest safe shutter speed for sharp handheld photos: 1 over the equivalent focal length. On a crop sensor, multiply the lens focal length by the crop factor first.
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