Why did my Canon 80D meter suggest 1 second in very dark pre-dawn light?
Asked 10/26/2019
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I was shooting a sunrise before dawn with a Canon 80D. It was extremely dark, about one day before new moon. For framing and focusing I raised ISO to the maximum and set f/8. The camera’s meter suggested about 1 second, both in Av mode and in Manual with the meter near 0. But a 30 second exposure gave a good result, roughly 5 stops more exposure than the meter suggested.
I saw the same behavior with evaluative and average metering. Once the scene got brighter and I could see landscape features by eye, the meter started behaving normally again.
Why would the camera meter be so far off in these conditions? Does the 80D meter stop being reliable below a certain light level rather than simply indicating underexposure?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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It sounds like the scene your were framing was outside the operating range of your 80D's meter.
It's rated for EV 1-20.
At ISO 100, EV 1 is equal to f/1 for 1/2 second.¹
The maximum ISO for the 80D is 25,600. That's 8 stops higher than ISO 100.
f/8 is six stops darker than f/1.
You report that 30 seconds was a good exposure time for ISO 25,600 and f/8.
30 seconds² is 5 stops brighter than 1 second.
Compared to EV 0:
- ISO 100 to ISO 25,600 = 8 stops brighter exposure (for an 8 stops darker scene)
- f/1 to f/8 = 6 stops darker exposure (for a 6 stops brighter scene)
- 1 second to 30 seconds = 5 stops brighter exposure (for a 5 stops darker scene)
The net difference is 7 stops brighter exposure than EV 0 which means your scene is 7 stops darker than "EV 0" and 8 stops darker than "EV 1".
Thus, the scene was well outside the rated range for the light meter in your camera.
¹ The "baseline" for Exposure Values is EV 0 which is f/1 for 1 second at ISO 100.
² For exposure times, 30 seconds is really 32 seconds. Set your camera to 30 seconds exposure and use a stopwatch to time it. The sequence is 1, 2, 4, 16, and 32 seconds. Many of the numbers we use in photography are rounded from powers of 2 to easy to remember base 10 numbers.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
6y ago
0
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Most likely the scene was below the 80D’s metering range, so the meter was no longer reliable.
The 80D’s meter is rated only down to about EV 1 (at ISO 100). Your exposure was much darker than that. Using your example: ISO 25,600 is +8 stops from ISO 100, f/8 is -6 stops from f/1, and 30 s is about +6 stops from 1/2 s. That places the scene around EV -7, far below the camera’s specified metering limit.
When you meter below the supported range, the camera may still display a reading, but it can be inaccurate rather than simply pegging the scale. That explains why it suggested about 1 s even though 30 s produced a good exposure.
So yes: in near-total darkness, the camera meter can effectively “run out of range.” In those conditions, test exposures, histogram review, and experience are more trustworthy than the meter. Once the scene brightened back into the meter’s operating range, it started giving sensible readings again.
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