Why doesn’t Canon Speedlite AF-assist work in AI Servo mode?
Asked 3/4/2013
5 views
2 answers
0
On a Canon EOS 7D with a 430EX II, the Speedlite’s AF-assist beam works in One Shot AF but does not fire at all in AI Servo. Why is AF-assist disabled in AI Servo, and is there any camera/flash setting or combination that allows it to be used in continuous autofocus?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
5
The AF-Beam is is used while the camera focuses but before it meters. Otherwise, metering gets affected and significantly so in condition when the AF-Assist beam may help.
In any type of Continuous AF this is not usually the case, so , the AF-beam must be turned off. A camera must also be able to keep focusing, so the AF-Assist beam could create a situation in which the camera knew where to focus but no longer can, should the AF beam be on but later turned off.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
13y ago
0
Generated from our catalog & community — verify before relying on it.
Canon disables Speedlite AF-assist in AI Servo by design. The main reasons are:
-
Continuous AF behavior: In One Shot, the camera can use the assist beam briefly while acquiring focus, then stop. In AI Servo, focus is updated continuously, so a temporary assist pattern is less practical—if the beam disappears or the subject moves beyond it, tracking can become unreliable.
-
Metering interference: The AF-assist beam can affect the camera’s metering. In One Shot this is manageable because focusing and metering happen in a more discrete sequence, but in continuous AF it would be more disruptive.
-
Low-light AF limitations: AI Servo uses shorter sampling/exposure time for the phase-detect AF sensor than One Shot. In very dim light, that gives a poorer signal-to-noise ratio, so AI Servo is inherently less able to focus in the same dark conditions where AF-assist would be most useful.
Based on the provided answers, there is no custom function to enable Speedlite AF-assist in AI Servo on this setup; this is a system limitation rather than a missing menu option.
Recommended products
UniqueBot
AI13y ago
Your Answer
Related Questions
Why isn't the AF-assist beam working on my Metz 44 flash with a Canon EOS 650D?
Can I use a Canon Speedlite's AF-assist beam without firing the flash?
Why doesn’t the AF-assist beam work on my Canon 430EX II?
Why does the Canon 430EX III use flash pulses for AF assist by default instead of the infrared beam?
How do I keep focus on a bird in flight with AI Servo on a Canon 7D Mark II?