I have many question

[Scott Whaley]

It could be simply user error. I practiced until I got it right. You can rehearse the correct way to do something or you can rehash something the wrong way.

 

[weepete]

I like back button focusing, been using it for years and it suits me. I use it all the time and I don't even think about it now. But I like the separation it gives.

But there's no reason it would give you sharper shots than a half press of a shutter button, both are equally valid methods of focusing and it's really just down to mechanics if you prefer one over the other.

It would be useful to see an example image of where you think BBF is the cause of your issues.

In your example your instructor seems to think that BBF can cause issues with matrix merering when really he's talking about focus recomposing and auto exposure lock.

Focus recompsing is just when you focus on something in the frame, then change your framing withour re-focusing. For example: if your centre focus point is the active focal point (assume single point AF), you focus on a person in the middle of the frame then, while keeping that focus move the camera until the person is now on a third line. That technique can cause it's own issues too.

 

[paigew]

I use BBF almost exclusively (besides when I manually focus), and have for years. I photograph kids, families, headshots, weddings/events, births, animals, school photography, nature photography. I shoot wide open, fast moving subjects, low light. I focus and recompose, I pan, I do everything with BBF and I have pretty high keeper ratio when it comes to focus. I personally think BBF is very important and I recommend anyone who asks me to use it. It is also important to note that I use the Al-Servo mode.