How accurate is the exposure meter?
With some exceptions, Cine Meter II tracks my other meters (Spectra Pro IV-A and Gossen Starlite) within +/- 1/10 stop from below 1 lux or 0.1 footcandle (about the level of a clear night illuminated by the full moon) to over 100,000 lux or 10,000 footcandles (full sunlight; I’ve measured up to 12,000 footcandles on a sunny day). The exact lower limit depends on the iDevice used, as their low-light limits vary.
The exceptions are:
Some devices show a 1/2 – 2/3 stop sensitivity shift between higher light levels and lower light levels. Below a certain level (roughly ISO 200, 1/60 sec, f/4) readings track other meters to within 1/10 stop. Above another level (roughly ISO 200, 1/60 sec, f/11) readings track other meters within 1/10 stop, but at a level about 1/2 to 2/3 stop higher (more sensitive) than other meters. If you calibrate at the lower levels, the higher readings will have you stop down half a stop too much; if you calibrate at the higher levels, your low-level readings will have you open up half a stop more than you should.
This sensitivity shift is baked into the iPhone’s “brightness value” metadata and affects any light-metering app, not just Cine Meter II. Unfortunately there is no other metadata available in the device with better accuracy, so there is no good way to bypass the problem.
The sensitivity shift affects iPhones SE, 6, 6Plus, X, XS Max, and iPad Pro; it does not affect iPhone 4S, iPod touch 5G, iPads 3 and 4, and iPad Air. Those are the ones I've tested with; it's likely that all recent devices (introduced after 2014 or so) are affected.
Cine Meter II versions 4.0 and later have a setting to compensate for the sensitivity shift.
Devices showing “computed brightness” above the toolbar when running iOS 8 or higher: these readings are often (but not always) within +/- half a stop of other meters. iOS 8 doesn’t report brightness metadata for the iPhone 4S, iPad 3, and possibly some other older devices; and iOS 9.0-9.1 don't work properly on 64-bit devices, so the brightness level has to be computed from the camera’s settings and the average picture level of the image.
Because iDevice cameras use their own exposure program optimizations, the camera settings and average picture level don’t match the actual scene brightness exactly. Cine Meter II uses an experimentally-derived lookup table to compute brightness from camera settings and picture level, but these readings are less precise than the normal readings. For best results with reflected-light computed brightness, meter a flat surface or low-contrast part of the scene using the spotmeter.
Modern iDevices perform a lot more image processing than older iDevices do, so Computed Brightness on newer iDevices (those introduced in 2014 or later) is less accurate, and should not be used.
Incident readings are accurate head-on, but may vary as the light is moved off to the side; depending on the diffusion used and the camera in your iDevice, side-lit readings may be as much as 1/3 to 1 stop lower than the readings on other incident meters.
How accurate is the color meter?
Once you've calibrated it, my best answer is, “it’s no worse than other cine color meters.” Under full-spectrum sources (tungsten incandescents, full sunlight) Cine Meter II typically tracks other color meters quite closely; under LEDs, fluorescents, HMIs, and similar “spiky spectrum” sources it disagrees with other meters, but no more than other color meters disagree amongst themselves! Under full-spectrum light Cine Meter II is typically within 100K–200K of other meters; under “spiky spectrum” lighting it’s usually—but not always—within 500K of other color meters; that’s comparable to the ranges by which other color meters agree or disagree amongst themselves. Here’s my DVInfo.net article testing various color meters under a variety of light sources; here’s a comparison of Cine Meter II to those other meters.
Why doesn’t the light meter match my DSLR / handheld meter?
Cine Meter II computes exposure based on the standard
APEX equation, using the assumed EXIF values for K and N. Its
default calibration matches my Spectra Pro IV and Gossen Starlite
meters very closely. However, it may not match your meters:
- Have you calibrated Cine Meter II to your reference meter?
- “A photographer with one light meter knows what his exposure is. A photographer with two light meters is never sure.” Once you’ve calibrated Cine Meter II to your reference, it should track very closely... as long as both meters see exactly the same angle of view, under the same color temperature. Meters (both handheld ones and built-in camera meters) differ in their color sensitivities and metering patterns, and it’s not unusual for two meters to match perfectly under certain conditions and differ by as much as a stop under others.
How do I manually set exposure and white balance for the picture and waveform display?
Cine Meter II doesn't let you preset an exposure. You can lock an existing exposure, but since your iDevice camera's response to light may not be the same as your production camera’s, there isn’t any point in trying to “preview” a set exposure on your iDevice.
You can lock the camera’s current white balance, or (with version 1.11+ on iOS 8 or higher) set it to 3200 K or 5600 K.
See How To for details.
Can I change the size of the spot metering area?
No, sorry. It’s set by the camera in your iDevice, and it isn’t adjustable. But if you’re running iOS7 or newer and have a recent iDevice, swipe up or right on the picture monitor to zoom in for a tighter reading.
Can Cine Meter II measure color temperature?
Yes! In incident mode using diffusion, Cine Meter II version 1.6 or newer running on iOS 8 or newer shows correlated color temperature and green/magenta tint in the upper right corner of the screen. You can also enable color measurement for reflected readings using a gray card or other color-neutral target.
Can Cine Meter II measure CRI, CQS, TLCI, TM-30, etc?
What about incident metering?
You can use diffusion or a Lumu Lite photosphere for incident readings.
To measure incident light, cover the camera with diffusion:
- You can tape a small piece of Lee 216 White Diffusion or similar material over the camera. Even a scrap of plain white paper works. As long as your material is color-neutral and you calibrate using it, you will get good results.
- DP Leonard Levy created the “Lenny Hat”: a paper hat for the top of
his iPhone. It covers both the front and back cameras. When he wants
an incident reading, he slips the Lenny Hat onto his iPhone. When he
wants a reflected reading, he pops it off and puts it in his wallet;
“that way I always have it with me.”
It’s easy to make a Lenny Hat: just fold a sheet of paper over the top of your iPhone, cut the front off level with top edge of the camera and waveform windows (do this with Cine Meter II in incident-reading mode: the windows move down to make room for the Lenny Hat in incident-reading mode on most iPhones), bend the edges around and tape them in place; pop it off and trim the sides and back level with the front.
- Luxi was a clip-on integrating photosphere; however it is no longer available. Practically speaking, a Lenny Hat works just as well.
Left: installing Lenny Hat. Center: using Lenny Hat. Right: using Luxi.
The original Lumu, now called Lumu Lite, is a self-contained incident-light sensor that plugs into your iDevice’s headphone port. Lumu Lite has been discontinued in favor of the newer Lumu Power, an incident, color, and flash sensor using the Lightning port on newer iDevices. Lumu Power is not supported in Cine Meter II.
I have a detailed review of Lumu Lite with more information. Lumu Lite is supported on all iDevices with headphone ports running iOS 6 and newer, starting with Cine Meter II version 1.4.
Lumu is a trademark of Lumulabs d.o.o. The Lumu name and logo are used with permission.
Where’s the lux/footcandle reading?
lux/fc appears when Cine Meter II version 1.4 or newer is used in incident mode.
How does the iPhone screen’s glow affect incident metering?
I took incident readings in low light (around f/1.4, 1/24 sec @ ISO 3200) using a Luxi diffuser on the front camera of my iPhone 5. With the screen brightness at maximum, compared to the screen brightness at minimum, I saw a 1/10 stop difference, as well as a color difference (in this particular situation) of +200 K and + CC 6 Green (1/5 full green). I tried shielding the Luxi from screen glow with black paper, and got the same results as I did from dimming brightness all the way.
In general, it’s not significant enough to worry about, but if you’re working in dim light it’s best to have screen brightness low (if you have auto brightness enabled, it will probably be low automatically). If you're still concerned, use diffusion on the back camera (or swivel Lumu to face away from you) for incident readings in low light.
What about flash metering?
Sorry, it can't be done reliably and conveniently using an iPhone camera. The Lumu Power is (as far as I know) the only way to properly meter strobes with an iDevice.
Where is the Android version?
I don't have one, sorry, and at present I'm too busy with iOS work to develop one.
How do I upgrade to Cine Meter II from Cine Meter?If you have purchased Cine Meter, look for Cine Meter Upgrade Bundle in the App Store, and select “Complete My Bundle” to save $4 (USA) over the cost of buying Cine Meter II by itself. [Note: Bundles don’t show up in the App Store app on iOS 6 or earlier; you’ll need to use iTunes on your computer to see it, or upgrade your iDevice to iOS 7 or newer.]
I’m a student: can I get a discount?
Both Cine Meter and Cine Meter II are available through Apple’s School Manager program. Your school can buy 20 or more at half price, and give you a code to install the app on your iDevice.
Why isn’t my question answered here?
Because I haven’t heard it yet, that’s why. Ask
me and I’ll see if I can answer it.
© 2014–2023 Adam J. Wilt. Last updated 2023.02.05