Again, all of these images are uncropped full frame. The vertical metal ruler approximates the size of a human head and neck. These are enlarged only to around 4x6 inches here (on my 23" video monitor, I don't know about yours). DOF is instead computed to standard 8x10 size, but I'm sure you must see the point. The dramatic way to eliminate a problem background is to crop it out, to simply remove it. We stood back with a longer lens, and still have the same view of the "subject", but we improved the background drastically... Simply removed most of it, and blurred the small remainder as well or probably better. Speaking of eliminating a problem background, even f/5.6 is very noticeably better achievement of goal, certainly better subject depth of field, but most of the background is blurred or simply gone now. Much better than including the house and the fence here. There really wasn't much we could do with the short lens, but the longer lens allows only a step or two sideways to critically select the best small part of the background to include, and to also to remove the worst part of it.

These images are not cropped either, except by the lens choice. The greater subject distance gives the 200 mm essentially the same field of view at the subject. But the 200 mm certainly does greatly crop the background, a big plus. And sort of like moving a spot light around, we can easily move the camera slightly to choose the best part of it. And the lens can enhance the DOF, another plus at the subject, and still be more blurred at the background.

IMO, even the 200 mm f/5.6 background is preferable to the 50 mm f/1.8. And f/5.6 certainly has strong DOF advantages at the subject. We have choices. We could pick better backgrounds, and subjects too, and there are many numerical combinations, but the longer lens is a very strong technique. It improves portrait perspective too. This is just a quickie test, with a hopelessly poor background to make a point.

Which above do you think could be the better portrait background? You did notice how much of the wide background is simply missing? The telephoto background is so narrow, making a step or two sideways is easy to select the most desirable part of it to show (or omit). Do you imagine stopping the longer lens down a couple of stops from f/1.8 could help the subject DOF?

Here are some blowups to better see the subject detail: (same pictures, full frame width, 33% size, 950 pixels wide. Shown about 25% larger than 8x10 size here on my 23" monitor).