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When I'm shooting outside in daylight and I'm adding one of my speedlites into the mix, I usually choose to shoot in Aperture Priority. This allows me to pick the aperture value while my camera chooses the shutter speed. It's a quick, easy, and efficient way to shoot. The aperture value I decide to use is mostly driven by the depth of focus I want to achieve. When I'm shooting head shots, for instance, I often choose an open aperture, generally the most open or widest aperture my lens allows. Doing this, of course, produces the shallowest depth of focus and helps "pop" my subject's head and face from the background.
When I'm shooting in a studio or other interior location, I mostly shoot in manual mode. That's because when shooting interiors I'm almost always using studio strobes, a.k.a. monolights or monoblocs, rather than speedlites. Monoblocs don't allow for automated or semi-automated exposure settings. (I also sometimes use monolights when shooting daylight exteriors and, when I do, I also shoot in manual mode... not that I have another choice.)
If I'm shooting interiors with a seamless or a blank wall as my background, shallow depth of focus is usually less important to me unless, for whatever reason, I decide I want the focus to be so shallow that, as an example, the model's eyes are in sharp focus and other parts of her face or body are soft, focus-wise, to varying degrees. Sometimes though, I will choose to shoot at wider apertures when shooting interior head shots of women, i.e., I'll aim for a very shallow focus, one where the subject's eyes are tack sharp but the end of her nose is going soft. This helps compress the face and is generally perceived as being more aesthetically pleasing for head shots of women. (Note: If I'm shooting head shots of men, I'm less interested in shallow focus because, in my opinion, the opposite holds true in terms of compressing a man's face.)
Back to shooting models in interior locations: As mentioned, if I'm shooting a model against a seamless or blank wall and I'm not interested in compressing her features, that is I'd like to see most all of her in relatively sharp focus, I'll stop down and shoot at larger f-stops, i.e., narrow apertures. I'm not trying to blur the background because a seamless or blank wall background is generally featureless so there's little to nothing to blur. For me, shooting at f/8 or f/11 gives me the results I'm mostly looking for.
Shooting at stopped-down apertures means I'm going to have to hit my model with more light, more intense light, to get proper exposure. That's not a problem since I'm using monolights and they're fairly powerful. Plus, I almost always have my lights in close proximity to my models since I usually want a larger light source (relative to the model) in order to produce softer, creamier light. Some shooters like to shoot at f/16 for these types of shots. While I rarely shoot at f/16 for interior portraits, there's certainly nothing wrong with doing so. For me, however, f/8 and f/11 produce enough depth of focus for my purposes. (When I'm not looking for a very shallow focus.)
The naked pretty girl at the top with the sexy/sultry expression on her face is Ally. I snapped this one of Ally with my Canon 5D (original) and a Tamron 28-75 f/2.8 lens zoomed in almost all the way to a 70mm focal length. ISO 100, f/11, 125th sec. Three lights and a reflector were employed: A Photek 4' Softlighter for my main light with a LumoPro Lite Panel under it, angled up for some extra fill from below. I also employed two small brolly boxes, either side from slightly behind her.