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Old 28th March 2011   #1
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How to Improve Low Light Performance on the X100

Last night, while experimenting I discovered a way to get better low light AF performance. One of the more challenging tests for AF performance is to shoot a lightly textured wall in low light but where there is enough light so the focus assist light does not come on. Many cameras I have tried this with fail to find focus under those conditions. For example the SOny NEX-5 couldn't do it but the Panasonic GF-1 could. What I discovered is that when the setting is AF-S the camera struggles to find AF failing frequently and when it does find it or at least indicates it has found it, it is slightly off. However, switch to AF-C and it is a different story. It instantly finds focus and confirms it and the focus is right on. The first image is the overall scene. I was focusing on the wall about 6" below where the thermostat and about 8" from the wall corner to the right. It took 7 attempts in AF-S mode before I got a green rectangle and I took the shot. I then switched to AF-C and in the first attempt i received a green cross hair and took the shot. The side by side are at 100% so you can compare the focus. Try and see if you get the same results. I had the apertures set to f2, shutter speed to 1/60 and AUTO ISO. I should add, it is very fast focusing this way and no hunting. It may use more battery but if you are shooting in low light you want to use this mode! I don't know how much the fact that it is focusing on a much smaller point using the cross hair contributes to the improved performance.

The test wall



Comparison between AF-S and AF-C side by side:



One could understand it being faster since it is continuously adjusting focus (by the way the Sony NEX is continuously seeking focus and it can't be turned off) but not the improvement in performance (ability to focus on difficult targets). I tried snap shooting in low light with this setting and I was surprised again. I would just rapidly bring the camera to eye, quickly put the cross hair on my focus target and push the shutter release all the way without waiting for confirmation. Shot after shot was in focus. The only irritation is hearing the focus motor constantly moving the lens when everything else is so quiet.

Anyone else with a camera try this and verify I wasn't imagining this?
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Old 28th March 2011   #2
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Re: How to Improve Low Light Performance on the X100

Just discovered another benefit of using AF-C. The camera will consistently focus down to 58 CM versus 80 CM. It makes a big difference in not having to switch to Macro.

I measured performance and the average (includes my reaction time) for 18 shots was 379.39 ms. Best case was 235ms and worst case was 503ms. My average reaction time was 170ms by shooting in manual focus.
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