Spot AF eh? Sounds like a great idea doesn't it? You know, use a smaller area of the AF sensor for more precise focusing?

Yes, we like the sound of that. Trouble is, it's not the answer to all your prayers and it's certainly not the  best AF mode to use on the EOS 7D by default. In fact, use it and you'll probably find it's not as good as you thought - unless of course you use it wisely. And that means only in situations when it's appropriate. 

The reality is that spot AF is good in bright light on fairly static subjects when you want to focus 'through' obstacles, or when shooting portraits and you want precise focus on the eyes. In all other situations, it's a bad idea to use it - it is slower to track and harder to keep the point on the exact spot you want to focus on. More than that, in low light, it takes longer to focus as well due to the smaller area of the AF sensor being active and therefore less low light sensitivity. 

In short, use it with static subjects, in good light, or when shooting portraits. For all other situations, look elsewhere in the four other AF selection modes for focusing nirvana. 

There are similar restrictions with the other AF modes too, especially Zone AF and AF Point expansion. But I'll save those for future posts. For now I just wanted to get Spot AF off my chest as I've had several emails about it recently.