🔍 Optics & Photography Tools

Near, far and hyperfocal distances — and why the one-third rule is true at exactly one distance, set by the focal length over the hyperfocal distance.

Magnification, extension, working distance and light loss — where 1:1 costs exactly two stops and brings the diffraction limit forward by the same two.

Field of view, total magnification and resolution — where going from 10x to 40x is four times narrower but sixteen times less area to look at.

Equivalent exposures across aperture, shutter and ISO — and why a stop doubles the time but only multiplies the f-number by the square root of two.

Stops, divisors and densities for neutral density filters — where an ND1000 is ten stops, is really 1024, and two ND8s stack to an ND64 rather than an ND16.

Star trail exposure limits by the 500 rule and NPF — where how wrong the 500 rule is does not depend on your lens at all, because the focal length cancels.

Light falloff by distance — where the same half-metre step costs two stops beside the subject and a sixth of a stop across the room.

Key-to-fill ratios in stops — where a "2:1 lighting ratio" turns out to mean both lights are set to exactly the same power.

Flash reach from a guide number — where doubling the distance takes four times the power, and the feet figure is 3.28 times the metric one.

Angle of view and crop factor for any lens and sensor — where halving the focal length gives 1.81 times the angle, not two, and the shortfall grows.

Print size, density and viewing distance — where the 300 DPI standard turns out to be human eyesight at twelve inches, and the real figure is 286.

Frames, coverage and overlap for a panorama — where ten frames at 30% overlap throw away 27%, and only the joins overlap rather than every frame.

Interval, frames, clip length and storage — where how fast time runs is the interval multiplied by the frame rate, and both matter equally.

Slices, step size and depth of field for a focus stack — where stopping down to shoot fewer slices runs into diffraction, and at 1:1 it runs into it early.

Where diffraction starts to cost you sharpness — f/21.6 or f/4.5 on the same camera, depending entirely on whether you measure against a print or a pixel.