How do manual flash power settings relate to flash exposure compensation?
Asked 6/11/2015
6 views
2 answers
0
On my flash, manual mode lets me set output from 1/1 down to 1/128 in 1/3-stop steps. In TTL or TTL remote mode, I can instead set flash exposure compensation, usually around -3 to +3 EV. Are these effectively the same thing, or are they different controls?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
3
Flash exposure compensation (FEC) shifts the metered exposure value for the flash by the set number of stops.
The power levels of the flash in manual mode are fractions of full output (1/1).
So if the TTL metering determines a flash power level of eg. half full strength (1/2) and you have dialed in a FEC of -1, the resulting flash output is 1/4, -2 would result in 1/8.
This is of course equivalent to performing this metering and calculation manually and setting the flash to the calculated power.
FEC is a bias, while the power setting is an absolute value (well, relative to max. power, of course).
Originally by user32110. Source · Licensed CC BY-SA 4.0
user32110
11y ago
0
Generated from our catalog & community — verify before relying on it.
They both affect flash output, but they are not the same control.
In manual flash mode, settings like 1/1, 1/2, 1/4, 1/8, etc. are absolute power levels: you are telling the flash exactly how much of its maximum output to use.
Flash exposure compensation (FEC) in TTL mode is relative. TTL first meters the scene and chooses a flash power automatically, and FEC tells it to use more or less than that metered value by a number of stops.
Example: if TTL decides the flash should fire at 1/2 power, then:
- FEC 0 = 1/2 power
- FEC -1 EV = 1/4 power
- FEC -2 EV = 1/8 power
- FEC +1 EV = 1/1 power (if the flash has that headroom)
So the stop relationships are the same, but manual power is an absolute setting, while FEC is a bias applied to whatever TTL metering chose. Also, FEC range may be limited if the flash is already near minimum or maximum power.
Recommended products
UniqueBot
AI11y ago
Your Answer
Related Questions
Why does my Canon 430EX II look brighter at manual 1/64 power than in E-TTL?
Why do Nikon TTL flash photos get brighter when I change exposure compensation?
Can the Nikon D7000 bracket flash output only around a manual flash setting?
How does TTL flash behave when the camera is in Manual exposure mode?
Why Flash Exposure Lock doesn’t work with Canon flashes in manual mode