7D Spot AF Selectivity

How selective is Spot AF on the 7D? 200% crops, lower right picture is the original. The camera wouldn't lock when the focus point was on her forehead. 55-250 IS, 250mm, ISO 3200, dim compact fluorescent lighting.

I'm not sure what you're trying to prove here. Are you saying that when the spot af point is on her forehead it won't lock?
Explanation: if your spot af covers an area that has no contrast, such as a plain area of a presons forehead, it will not lock.

In the second picture the AF point seemed to have locked on to the edge of the picture frame, I think that's normal since it's where the AF point fell.

Also keep in mind that at ISO3200 there is noise reduction going on in jpeg mode, and you're showing us jpeg. NR will soften detail.

By the way even the spot AF extends a bit beyond the edge of the AF square.

Also, what was your shutter speed?

What I'm demonstrating is how small the AF point is in Spot AF mode. When attempting to focus on her forehead with Point AF mode, the camera will lock because of the contrast in the area beyond the marked point. With Spot AF, the point is so small the camera can't lock because of the lack of contrast in that tiny area. I'm not concerned with noise reduction or softness in the image, it's a sample of how selective and sensitive the Spot AF mode is. Shutter speed was 1/100 second and the JPEGs are small fine, SOOC with standard high ISO noise reduction. Not meant to be wall hangers.

Judging by the images in the original post, it looks like your 7D is functioning perfectly, congrats.

I would agree the camera did what it states in the manual. There is warning about lack of contrast and failure to focus. Hence the options for focus methods. Lighting In addition to poor contrast would explain the lack of focus lock on the forehead.

oldvultureface wrote in post #9636981
What I'm demonstrating is how small the AF point is in Spot AF mode. When attempting to focus on her forehead with Point AF mode, the camera will lock because of the contrast in the area beyond the marked point. With Spot AF, the point is so small the camera can't lock because of the lack of contrast in that tiny area. I'm not concerned with noise reduction or softness in the image, it's a sample of how selective and sensitive the Spot AF mode is. Shutter speed was 1/100 second and the JPEGs are small fine, SOOC with standard high ISO noise reduction. Not meant to be wall hangers.

ahaa! I see now

eosphotomanoftennessee wrote in post #9637087
There is warning about lack of contrast and failure to focus.

I'm actually happy it wouldn't lock on her forehead. That means the Spot AF point is seeing a very small area. This mode would be great for isolating birds among tree branches or zoo animals behind fences.