I got my new tripod and 50mm F/1.4 sigma on my Nikon D7000 and was testing it out doing some shots of a flame on a candle.
The below image is the sharpest i was able to produce. In review of my 50+ shots I noticed very many out of focus. This is the main factor I was trying to concentrate on to get a clear sharp picture of the flame.
Using Manual Focus
A few things I noticed and could use help with are the act of manual focusing on the flame. I would try to use my eye and view the flame in the eye piece. I would turn the auto focus ring back and forth dialing it in to a point in between both extremes until the flame looked sharp. I noticed there was considerable travel in the focus ring while still looking sharp to my eye. How can I tell when the flame is in focus? When and how do I detect where to leave the focus ring in order to get a crisp and sharp photo?
Using Auto Focus
I took about half my shots using Auto Focus and found a great many of these shots were also not sharp. I guess the auto focus had a hard time with the only light being the candle. I turned on the lights and used a cardboard post to try to get the camera to lock cardboard and then turn off the lights and light the candle. This was also not a help and my attempts seemed very crude. Should I and how can I use auto focus in this situation?
Also, I found it annoying that when I tried to get the auto focus to lock on a particular point on the cardboard the camera kept selecting some other point of focus on. At least this is what i gather was happening because the camera placed a black little square box on a section of the frame other than where I intended it to. How can I control this box so I can tell the camera what I want to focus on?