DOF: When is shallow too shallow?

[Ian_of_glos]

There is no right answer to this, because it really depends what effect you want to create. You might want the shallowest possible depth of field in order to focus attention on one particular item - a ring on the model's finger, or an award that the model is holding for example. Alternatively you might want to show the model in context - a workman in a workshop or a chef in the kitchen. For this type of picture you will want the background to be in focus, even if it is not as sharp as the actual subject.
Recently there has been a lot of discussion about bokeh and the quality of bokeh, almost as if it is a separate and competing subject in the scene. However, to me it is just a way of removing a distracting background by throwing it out of focus, or at least making it so out of focus that you cannot tell what it is. It is an alternative to over or under exposing the background, changing the shooting position so the distracting background is no longer in the frame or using an artificial background. All these techniques are valid and will come in useful from time to time.
In the studio, where I am able to control the light and the background I don't worry about depth of field and just use an aperture that is somewhere in the middle - F8 usually.
Outside, sometimes I deliberately use a narrow aperture because I want the background to be sharp, for example a farmer leaning on the farm gate with the rolling hills in the background. At other times the background might be so ugly that I want to throw it completely out of focus, and that might mean that only the model's eyes are really sharp and the ears and nose are beginning to blur.

 

[Jack Douglas]

As a novice I'm appreciating all these comments!

Jack

 

[ethanz]

You can actually have both bokeh and full subject in focus with this:
https://petapixel.com/2014/07/28/bokeh-problem-focus-backgrounds-hold-can-get-fast-prime/

;D fake bokeh FTW!

That's actually a pretty cool idea.

 

[stevelee]

A distracting background can be just about as distracting when out of focus. Pick your backgrounds if you can, and don’t expect blurriness to cover your laziness.

A blurry background that calls attention to itself is calling attention to itself. No matter how poetic you wax in fractured Japanese, you are missing the point of the picture, unless the point of the picture is that my fast prime is better than yours at blurring things.

With a bad combination of focal length, subject distance, background distance, and aperture, a portrait can look more like a picture of a cardboard cutout or the Photoshop equivalent.