LumoLabs: Pentax K-5 low light focus study is published

Started Feb 23, 2011 | Discussions thread
falconeyes
OP falconeyes Senior Member • Posts: 1,437
Re: LumoLabs: Pentax K-5 low light focus study - interpretation

Kerusker wrote:

I Understand that. But why does the PAF system have these values for the blurred image:
AF Predictor: -26
AF Defocus: 13

If this is what you meant, then you're very talented to not word the question you want to ask.

I've noticed the AF Predictor / AF Defocus myself. I don't know what they mean but above values are in a "normal" range.

My general observation is that AF Defocus tends to be larger at lower light levels and becomes around 0 in full sunshine. I guess the AF system has an accuracy target depending on available light. If there is noise in the loop, then a refocus operation would not aquire perfect correlation values and you need a criterion when sharp is sharp enough.

BTW, both values are written into EXIF for MF or contrast AF as well. So, it is possible to run a MF series and measure both, AF Defocus and real defocus (e.g., using my method). You then could correlate both and we'll know.

AF Predictor could be related to the AF.C algorithm which would have to focus behind or in front of the target.

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