Cine Meter

SEE the light: Cine Meter gives you an RGB waveform monitor and a false-color picture in addition to a cine-style, shutter-priority reflected light meter, using the camera in your iPhone / iPod / iPad.
• The light meter shows you your stop as a decimal value (such as f/5.0, good for cameras with EVF iris readouts) or as a full stop and fraction (like f/4.0 ⅔, good for cine lenses with marked iris rings). You can calibrate Cine Meter to match other meters to a tenth of a stop.
• The waveform monitor shows you how light levels vary across a scene. You'll see how smooth and even the lighting is on a greenscreen or background, and find subtle hotspots and shadows at a glance. The waveform’s RGB mode shows you color imbalances in the image and gives you a handy way to check color purity and separation for chroma-keying.
• The false-color mode lets you define allowable contrast ranges, and see instantly which shadows are underexposed and what highlights risk clipping.
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READ BEFORE YOU BUY:
Cine Meter is NOT a color-temperature meter; it can't measure white balance.
It's NOT a flash meter; it can't measure strobes.
It's designed solely for cine/video work and isn't optimized for still photography; for example, it's shutter-priority only.
Cine Meter gives you *absolute* light meter readings, but *relative* picture and waveform monitor levels:
1) Cine Meter’s picture and waveform monitor do not use the *exact* exposure shown by the light meter (they are close to the meter reading, but can differ from it slightly). The picture and waveform monitor show you *relative* levels within a scene, not *absolute* levels based on the meter reading.
2) You can't *preset* exposure or color temperature in Cine Meter. To compare exposures and colors, you lock Cine Meter’s auto-exposure and auto-white-balance settings while looking at a known good reference, such as a gray card. The picture and waveform monitor then show you levels and colors relative to your locked settings.
See http://www.adamwilt.com/cinemeter/details.html#How_It_Works for details.
(Why am I telling you this? I would rather have you understand these limitations up-front and not buy Cine Meter, than have you buy Cine Meter unaware of them and be disappointed.)