My comment is that it can't happen like that, that nice Mr. Newton explained why, and and there's simply no way that the immutable laws of physics can have taken a holiday, despite the weather
There's some light hitting the background here that we don't know about, there's no other possible explanation.
Poor Helen is being criticised about her poor lighting. OK, it
is poor, and the flare has created most of the apparent unsharpness, but she is actually asking about the perceived focus problem - which as I have already explained, is actually much less obvious on the raw image she sent me than on the smaller version that she posted in the other thread.
Helen, take Hoppy's advice on avoiding the flare. And take his advice on using just one light for now, life is difficult enough without using more lights than you need.
The poor souls who have talked themselves into coming on my lighting masterclass in a couple of weeks will be surprised at how many lights I have, but they will also be surprised at how few I actually use, most of the time, for most subjects.
There is only ever 1 key light, because there is only one sun. That key light does something like 90% of the work. Any other lights just add a glint here, fill in a shadow a bit there, add a bit of an edge somewhere else etc - your fill light isn't a fill light at all, it's a second key light. It's doing the opposite of what it should be doing.
You've been given some good advice on depth of field, but some of the advice is wrong, or is over complicated. If you want to really understand depth of field you need to have a fair understanding of physics, it isn't as simple as the charts and calculators make it seem. Personally, I keep a DOF calculator in my head, but to keep it simple, I think in terms of effective aperture (the size of the lens opening) not f/, because effective aperture is constant regardless of F (focal length) - f/ isn't.
For now, just shoot your portraits at f/8, focus on the eyes and don't worry if the ears are a bit out. Don't go smaller than f/11 on your camera, because you will lose sharpness due to diffraction limitation. Don't go (much) larger than f/8 because your lens probably isn't capable at larger apertures, and anyway it takes skill and a bit of luck to nail the focussing at large apertures. You need to stop running and start walking, slowly - there's a lot to learn and it makes sense to walk before you can run, and to concentrate on just one thing at a time.
Coming back to my lighting masterclass, I will probably take some shots at f/2.8 with a F200 lens, where the DOF will be virtually non-existent, and on a camera with much larger sensor than yours - but that will be with manual focussing with a lens that actually delivers at f/2.8, and probably 3 out of every 4 shots will be out of focus. You don't need that hassle.
Working in a small white room will lighten it a lot from the standard inverse-square-law fall-off (which would be something like 2-3 stops drop in that situation) but if that is indeed the case then you need to think about those black drapes we talked about previously as you will have zero lighting control without.
