Originally posted by falconeye [*]The paper clarifies conditions to hit or avoid the issue. White light (halogen is not white enough though) and a wide lens stopped down help to work around the problem.
AF assist light typically doesn't help though. But an LED flash light does.
First, big thanks for your paper...
Falk, I confirm that on my K5 (with the last known firmware), the AF assist lamp goes off several times while focusing (I was one of the two persons that reported this in the other thread, Chris Tham and me).
With my FA50/1.4 mounted, in dark situations, the AF assist lamp will fire once before moving, then, if it's really dark, for nearly each micro-adjustment (which is to say, usually, only one). If I voluntarily mess with the AF module by moving the camera while it focuses (panning or traveling), the AF assist lamp blinks up to 4 times (3 micro-adjustments) before AF fails...
The resulting pics seem to be focused, contrary to my other, AF-Assist-free low-light pics...
I'll have to check with the 18-55, if the behavior is the same...
EDIT:
I've done tests with my 18-55WR and my Tamron 70-200/2.8... In both cases, the behavior is identical to the FA50 : the AF assist lamp will blink as long as needed to lock AF (up to 4 times).
Focus accuracy is good in each instance (took about 20 pics with both lenses), while without AF lamp the K5 will FF quite a bit.
So
in my case the AF assist lamp does work.
An interesting point I've found is that the camera will behave identically (obvious FF) in the following situations:
- AF assist lamp disabled.
- AF assist lamp enabled but blocked by the hand.
So maybe the problem lies in the fact that the camera may not actually compensate for low-light (I don't know if this is indeed needed?), as it thinks it will have the AF assist lamp anyway... So, about at the same time the assist lamp should kick in (even when disabled), the '+' sensor is not considered anymore (as it would mess with the green beam focus, I think).
This could be partially dismissed by Falk's findings that the light color has no real impact, but I think this is not really proved yet, as using a blue filter in front of a tungsten bulb is different from having a true daylight (or pure blue) source.
EDIT 2:
Going through tests again, I've found out that the AF assist lamp will come on more easily with the FA50 than with the 18-55!!!
I mean that, in the same lighting situations (where the K5+FA50 will start to use the AF assist lamp for low-contrast targets), the K5+18-55 will hardly ever use it (and will end with blurred pics)...
This is quite the opposite to what I'd have thought...