So, found a decent location in the woods:
To explain my choices and I admit to being a relative newbie in this type of shot: I used an 85mm (1.8) lens to get the shallow depth of field, and still be in working distance of Amelia. This was shot at 1.8, so I would suggest using something around 85mm at the widest aperture possible (f2.8 on your Tamron?) Also, keep and eye on the distance your background is from your subject, the reason this has this type of bokeh is that the background is 20ft+ away, and has highlights on it so that'll make the specular highlights (bokeh balls). Also, get to the subjects level (if it's children, dogs etc) try not to shoot from above them.
For autofocus, I was in AF-S Single point with the focal point moved the the one covering her eye, the shot was composed like this in the camera not after in post production. I wanted to ensure I nailed focus on her eyes, I did not use AFC as it's quite difficult to nail focus on the eyes, and she was relatively still at this point.
I then metered the shot and it was suggesting something like 1/60th at 1.8 ISO 100. Always keep to your lowest ISO possible to keep get the best IQ. I'd want to use at least 1/200 on my 85mm lens to guarantee no camera shake. So may have upped the ISO a touch if I wasn't using flash.
Now if I had left it at that, I would have had a nice shot. But I introduced a flash in a octobox to light Amelia so I can control the exposure on her AND the background separately, without a light on her she would have been exposed nicely but the background would have been too bright (for my taste). So I rolled the shutter speed back up to 1/200 to darken the ambient exposure and added a flash in a octobox to the above/side of Amelia set in TTL (easier to let the camera meter for that when trying to get a toddler to stand where she needs to). I then took the picture about 20 times to get a half decent posed one
Here a picture of the flash setup, it was lower for shots of Amelia and more directed into the clearing, was trying something else when this was taken.
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