絞り、シャッタースピード、ISOの間で同等露出を計算。クリックごとに正確に1段ずつ変化し、1段未満の調整やEV表の出力にも対応。
| 変更する項目… | 露出を合わせるために調整する項目… |
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1「段（ストップ）」は光量の2倍または半分を表します。ISO感度を2倍にする、絞りを1段開ける、シャッター時間を2倍にする、のいずれも1段分の増加になります。等価露出ではISO段数 + 絞り段数 + シャッター段数の合計が一定に保たれます。
ISO 100でのEV = log₂(N² / t)。Nは絞り値、tはシャッター秒数です。カメラのダイヤル刻みに合わせて1/3段単位で調整します。
The headline figure is exposure value at ISO 100: EV = log₂(N² ÷ t), where N is the f-number and t is shutter time in seconds. The default f/8 at 1/125 s gives EV 12.96. Underneath, the Δ from base readout counts stops of brightness relative to the ISO 100 · f/8 · 1/125 reference by summing log₂(ISO ÷ 100), log₂(64 ÷ N²) and log₂(t × 125) into a single signed number.
The three dropdowns are ladders of genuine camera values: ISO 50 through 102400 and apertures f/0.95 through f/32 in third-stop increments, shutter speeds 30 s down to 1/8000 in whole stops. Changing one axis moves another to hold the exposure matched, and the Lock ISO, Lock Aperture and Lock Shutter buttons take that axis out of contention — click again to release. Reset (ISO 100 · f/8 · 1/125) returns everything to the reference.
Check the compensating value against your camera before you shoot. The tool snaps to the nearest ladder entry, and because shutter is a whole-stop list while ISO and aperture are thirds, a third-stop change can round away to nothing on the shutter axis. It is also pure light arithmetic: no reciprocity failure, no ND filters, no T-stop transmission losses, and no accounting for the depth of field and diffraction that separate f/1.4 from f/16.
It is log₂(N² ÷ t) for the default f/8 at 1/125 second — a measure of how much scene light that combination is set for, roughly bright overcast daylight. Higher EV means a brighter scene, and each whole number is one full stop.
Four times faster. Each stop doubles the light, so two stops is a factor of four: f/8 at 1/125 becomes f/4 at 1/500. ISO could absorb the same change instead, dropping from 400 down to 100 for an identical result.
The shutter list follows the classic camera dial, 30 s down to 1/8000 with each entry double the last. ISO and aperture use third-stop ladders instead. A one-third change on either can therefore round back to the same shutter value.
They pin one axis so it will not be moved when you change another, and clicking a second time releases it. Use Lock ISO when your camera sits at a base ISO you want to keep, or Lock Shutter to protect a motion-freezing speed.
Yes, at the same shutter speed. Doubling ISO adds a stop and opening f/8 to f/5.6 adds another, so both combinations land at the same brightness. They differ in noise and depth of field, neither of which this calculator models.
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