Having a debate with myself that F/10 makes my portraits look better by making faces have less "depth."
What I mean is I feel like wider apertures such as f/4 make my nose look longer and wrinkles more pronounced.
Are there any facts to backup this perception? Or am I just seeing things?
Usually it's focal length that is the key consideration for portraiture, at least in terms of making the subject look "good". (I use the term loosely; good is subjective, but let's assume people don't necessarily want to see representations of themselves with huge chins and noses.) You don't mention the focal length of the lens you are using, or the effective focal length you are getting because of any crop factor.
Aperture is a consideration, too, of course, but the main effect is changing the depth-of-field. The "size" of the focal plane (I know, I know, more hand-waving) is more about presentation and aesthetics, though lenses are often sharpest away from either end of their aperture ranges, often 1-2 stops from their maximum.
So, to answer your question, if you are seeing something good at f10, go for it. This aperture is also quite "typical" setting for portraiture (that is, the "typical" aperture is in the f8 range for most longer lenses used in head-and-shoulder portraiture), mostly because it gives you a nice balance of subject focus with less sharp backgrounds. How you use the depth-of-field and sharpness will certainly change how the subjects look.
But, I'd expect smaller apertures to yield sharper images (all other things treated equally), with more pronounced wrinkles, etc., as well as adding more background detail in. The latter may be what you want, or it may be distracting and lessen the impact of the portrait.
In terms of geometry, no. If you take two photos at the same focal length and distance from the sensor, but with different aperture, all of the elements in the frame will be in the same place (with possibly a small variance due to focus shift). The effect of longer noses or flattened faces is due solely to subject distance (which is related to focal length because focal length determines how close you need to be to fill the frame.) More on this at What does it really mean that telephoto lenses "flatten" scenes?, including nice visualizations.
But, I don't think your perception is completely crazy. Human attention is naturally drawn to areas of focus, and if the wrinkles and nose are sharp against a soft background (and possibly soft ears and rest of the face) in your large-aperture, shallow depth-of-field portrait, they'll stand out more. This is one of the reasons for the rule of thumb suggesting that when DoF is shallow, make sure to focus on the eyes — Should both eyes be focused in a portrait? — but, of course, if there are many wrinkles around the eyes, they'll stand out too. (So, a choice: retouching? soft focus? or, brutal honesty....)
The basic answer is No. You are seeing things. With a few possible exceptions.
There is a little, tiny, small chance that the wider aperture blurs wrinkles away from your focus point (the eyes vs. the neck for example) by making them out of focus.
The nose thing is a matter of perspective. The wider the lens is, the closer we tend to shoot, and the greater the distortion.
The longer the lens is, the further we tend to shoot, and the lesser the distortion.
The wrinkles part is a matter of light. The diffuse light diffuses the wrinkles, the position, the size of it, the contrast with the shadows.
Portraiture is an art and a science. Good portraiture is a mix of skilled lighting, skilled posing, and skilled camera positioning and astute selection of equipment. That being said, art is has no rules and you are free to follow your heart.
As to what aperture to use: Large working lens diameters yield shallow depth-of-field. In the vernacular, this is called “boken” from the Japanese for the aesthetic quality of image blur that accompanies out-of-focus image areas. Boken results when depth-of-field is set shallow resulting in eyes in focus, ears and nose bordering on blur, foreground and background blurred.
As to a larger nose which is accompanied by ears too small, these are functions of incorrect perspective. This phenomenon is induced when the camera to portrait subject distance is too close. The countermeasure is just to step back. Because it is human nature to compose a portrait with little extraneous surrounds, it can be difficult to force oneself to step back. Therefor the best countermeasure is to employ a moderate telephoto. Use of this longer than “normal” lens forces the photographer to step back. The result is a more true-to-life perspective that will mitigate facial distortions induced when the camera is too close to the subject’s face. Commonly, portrait photographers gravitate to a lens 2x thru 2.5x of “normal”. Normal for the Fx (full frame) is 50mm so the portrait range is about 100mm thru 125mm. For the Dx (compact digital), normal is 30mm so the portrait range is 50 thru 80.
As to wrinkles being pronounced: this is a function of the harshness of lighting and the perceived sharpness of the image. Generally the sharpest aperture setting is two stops down from the maximum diameter (generally about f/8. Also, higher contrast lighting usually results in the shadows going void of detail. This will increase the apparent sharpness. The countermeasure is the use of diffused lighting, or a fill lamp, or placing the subject where the light is indirect.
