I own a Canon 7D, overall its a pretty good camera, but i find its AF performance in low light shooting conditions unsatisfactory for a semi-pro camera that is spec up to ISO3200.
To understand the low light shooting performance of Canon 7D (or other Canon DSLRs) under 'AI Servo' and 'One Shot' mode better, i tried out the following AF sensitivity test at http://eosdoc.com/manuals/?q=AFSensTest
, with a Canon 50mm F1.4 lens and single point focus, center AF point.
It would be much appreciated if fellow Canon 7D owners out there could try out the AF sensitivity test too and comment which patch number is your camera able to focus down to, consistently, without hunting/hesitation when in 'AI Servo' and 'One Shot' mode?
Do note your patch number, f-stop, shutter speed and ISO setting. I use spot metering (center AF point) to obtain exposure readings.
From my test, I find that:
(i) the center AF point is most sensitive and can achieve clean focus (no hunting/hesitation) in lower light conditions better than all the other AF points.
=> this is probably due to the higher sensitivity (2 times more sensitive?) center AF point.
(ii) With single center AF point, 'Single Shot' mode, I can achieve clean focus (no hunting/hesitation) down to about patch no. 8 @ 1/60s, f1.4, ISO 1600 (= EV 3).
(iii) With single center AF point, 'AI Servo' mode, I can achieve clean focus (no hunting/hesitation) down to patch no. 35 @ 1/60s, f1.4, ISO 800 (= EV 4).
=> Performance is much poorer in 'AI Servo' mode compared to 'One Shot' mode. About 1 stop lower AF performance compared to 'Single Shot' mode in my test.
Canon specifies EV -0.5–18 for the 7D AF sensitivity.
How is this derived?
My test result seems to indicate (my) 7D is not performing within this range.
I would prefer/like to use 'AI Servo' focus mode for low light shooting situations, especially for (slow) moving subjects, but the Canon 7D 'AI Servo' focus does not seem to be able to cope well with it at all, leaving me with no choice but to use 'One Shot' focus, hopefully, for with better results (very frustrating to get moving subjects in focus), although the camera's image sensor (ISO performance) can still cope with the available light level.
Have a go at the test, I look forward to hearing from you on your test results and comments.
Is your Canon 7D (or other Canon DSLRs) AF having similar (or better!) AF performance characteristics?