Aperture and Shutter Priorities, When and Why

CRR_3158_001_big_mouthIn a previous post I discussed the Manual camera mode setting, its implications and recommendations of use. As a reminder for my conclusions: Manual mode is my choice in a controlled, low pace environment, or when a maintainable setting is viable. In any case, I turn on the auto-ISO sensitivity selection. This mode is the perfect setting to control any choices of adjustment or to practice different creative possibilities.

In this post I will discuss the so-called semi-auto modes: Aperture and Shutter priority modes.

The Aperture Priority mode

It’s a common belief that the Aperture priority (AP) is the preferred choice of most profesional photographers. Back in the 1980, the famous Nikon F3 was a camera primarily for AP mode. But why the preference? Now, in digital terms, if you combine this mode with the auto-ISO, you are always under the proper exposure, being the shallow or strong depth of field (DoF) your only setting concern. There’s no «bad» aperture under this mode under plain daylight conditions. With good lighting conditions the AP mode is the most fast setting, because your Shutter speed would go to high numbers, while the ISO values would go down to the lowest numbers, allowing you to quickly decide the DoF as desired. During daylight I always choose AP with the auto-ISO setting on. Under the Nikon ecosystem, I set my ISO sensitivity standard to 100 with a maximum ISO of 3200 (nowadays, up to 6400 for indoors shooting), with a minimal Shutter speed of 1/250th of a second. If for any moment I enter into a dark area or an interior with low light, the camera will decrease the Shutter speed to 1/250th, and only then my default ISO (100) starts to increase, if the light degrades. In extreme conditions, when the ISO scales to 3200 (or 6400) the camera starts to decrease the Shutter speed below 1/250th. Normally, in those conditions, I’m aware of the very-low light and try other options to avoid underexposure or camera shake. The message I’m trying to share is that AP gives plenty space for maneuver, maintaining a proper exposure, under a different, opposites, scenarios.

But then, it raises the question: is the AP the only or best choice for low light scenarios, interiors, night photos? Under low light conditions, the selection of lower f-stop numbers (little apertures) would require too low Shutter speeds and high ISO values, with the well-known consequences of blurred images and noisy pictures. The liberty to choice the DoF is absent without other extra measures. The first problem—the blurriness by camera shake or by subject movement—could be solved with a tripod and still subjects, but the noisiness is difficult to overcome in very low-light scenarios. When possible, the flash, properly used, is the correct choice. But again, this is an alternative only under controlled circumstances, not for night street photos or low-light events. In those situations I prefer to set my Shutter speed first, just for the scenes that I expect.

The Shutter Priority mode

I almost always choose Shutter priority (SP) over Aperture priority for those low-light situations. My starting speed is 1/250th of a second. This speed will eliminate any of the annoying situation of blurriness for any shake of my trembling hands, and also will freeze people of most common movements (walking, talking, even running slowly). Under this setting, the camera would open the aperture of the lens to the max (f/1.4, f/1.8 or f/2.8 according to your lens) loosing DoF. When the camera reach this threshold, it starts to increase the ISO (if auto ISO is on) to higher numbers with the noisy effect in your photos. Let’s discuss those implications.

In low light conditions, without the control of a studio, there’s no point to think about long DoF, for obvious reasons: there’s almost no light. Do you remember Rembrandt paints? Low-light scenes are like chiaroscuro paints: spots of light over a sharp subject. How can I reach great DoF, when my subject is under a street light in a dark park? The same circumstances will occur in a concert or in an interior event. Rarely under those scenes, you would pretend to deep the extension of your vision, before and after your main subject. Besides that, if you’re in indoors, it’s probably that you wouldn’t have too much field to cover. Open the lens to the max, as the SP automatically does, is the natural behavior in those scenarios.

How about the noisiness in low light scenarios? One of the greatness of “prime” and fast lens (fix length lenses with a maximum f-stops in or under f/2.8) is that they allow one or two additional stops for good exposures under low light conditions, before affect your ISO settings. Only after you reach the maximum f-stop number, the ISO starts to increase in SP, up to the max of your camera or your particular setting (mine is 3200 or 6400). Once again the possibility of using a flash should be considered. In other circumstances you might risk the quality of your pictures increasing your max ISO to 6400 or more. In these days the full frame (FF) cameras supports high ISO values of 6400 or more with «acceptable» quality. For APS-C cameras I wouldn’t go more than 3200 in most situations, or up to 6400, if you want the noisy effects for artistic expression.

Alternative: Spot Metering for low light conditions

There is another option we should consider: change your Metering mode to spot. For me, it has been very convenient to program one of my configurable buttons (reachable during shooting without leaving the viewfinder) to change the metering mode from matrix/evaluative (my default) to spot metering. This possibility allows me to get the right exposure for my subject by pushing the button while directing the focus-point to it (I use single point auto focus). With the programmed button, you don’t have to stop your shooting workflow if for any reason the subject receives back light, for example. And also, it always hit the mark with the proper exposure when only your subject receives the light in a dark room or stage. (That also applies on the contrary, when your subject is surrounded by a very luminous environment.)

Conclusions: use AP in normal good lights conditions (regular daylight in the street or very illuminated interiors). Otherwise, use SP with your minimal Shutter speed (1/250, e.g.) for interiors and minimum light scenarios that you can’t control. Consider to use flash and a tripod if you could plan your shots or have any control of the environment. Notice that my comments don’t consider camera o lens special features like image stabilization or vibration reduction. With that kind of features your settings could be more flexible for low speed shots.

Last question: Is there an opportunity to use the Program mode?

That will be discussed in another post.

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