Your Camera’s Automatic Modes…How does one choose?

Basics
Indulge me for a moment as we start at the beginning…  Most cameras have the following exposure modes:  aperture priority, shutter priority, fully automatic, and manual.  Your camera may refer to these as A, S (or Tv), P, and M.  In addition to automating the choice of aperture and shutter, many cameras also give you the option of automating ISO, the third “leg” of what’s often referred to as the “exposure triangle”.  Aperture relates to how big the opening is inside of your lens (which lets light in).  Shutter speed describes how long the internal sensor (used to be film) is exposed to that incoming light.  And ISO describes how light-sensitive the sensor will behave (or how light sensitive the emulsion on the film was). 

Optical Effects
No matter what mode you choose, the objective is the same…find a combination of these three parameters that will give you proper exposure and do so in a way that also achieves the optical results you desire for that image.  By optical results, I mean controlling your depth of field, motion blur or freezing, and noise and grain.  Because proper exposure can be achieved by a variety of combinations of shutter speed, aperture, and ISO, you will need to understand how each of the cameras settings affect the outcome.  The reason your camera has multiple modes to choose from is to help you zero in quickly on the right combination of settings for the particular image you’re working on capturing. 

Manual Mode

So, first let’s discuss manual mode.  Some professional photographers and advanced enthusiasts will claim they only shoot in manual mode as if it’s somehow a badge of honor (it’s not by the way).  Manual mode forces (allows) you to choose the three legs of the exposure triangle necessary to achieve a proper exposure.  You could say it gives you maximum control.  In contrast, automatic modes will help you by allowing you to choose one of two of the more important legs, and will then automatically choose the third leg necessary to complete the proper exposure.  There might be times or reasons why you would want to shoot in manual mode, but I think those times are so few and far between, I would suggest to you that manual mode be reserved for those rare occasions.

Semi Automatic Modes

Before you decide which automatic mode to use, you typically determine which parameter is most important for you to control yourself.  That is, are you primarily concerned about depths of field, i.e. how much of the subject matter is in focus, or how much subject motion you want to allow.  You generally want the ISO to be as low as possible for image quality, but sometimes this will be the parameter you will want to adjust higher knowing that you’re in low light situations and would want to be able to have higher shutter speeds and/or greater depth of field. 

As I mentioned, you can choose from aperture priority, shutter priority, and fully automatic.  You might be asking yourself, is there a “best” mode to use?  Well, let’s consider that question for a moment and see if you begin to formulate your own conclusion… (hint, the answer is no).

Pros and Cons of each Mode

Let’s start by looking at the downside, or “cons” to having an uncontrolled (automatic) parameter.  If you choose aperture priority (A), shutter speed will be automatically determined by the camera (and not you).  You have control over depth of field (aperture), but the downside then is that you could end up with too slow a shutter speed which would result in your main subject being blurred.  The number one reason most images will be discarded is because of lack of focus or a blurred subject.

If instead, you choose shutter priority (S or Tv), the aperture is automatically determined by the camera (and not you).  In this case you will have properly managed the motion blur, but the depth of field may be very shallow or may be deeper than you wanted.  Although this is a downside, too deep a depth of field can often be dealt with in post processing--too shallow a depth of field though is a greater downside if your subject does not fit within the depth of field (often the case in macro photography).

If the ISO is automatically determined (by the camera, not you), then your image could have a higher amount of noise or grain than you would want, but recognize that the only reason the camera is choosing a higher ISO is because you’re forcing it too when you choose a faster shutter speed or a smaller aperture opening in low light situations.  The grain and noise can be a downside, but you just need to be aware of this when shooting in low light (and when you don’t have a tripod that would allow you to use slow shutter speeds).  Also note that software can be used to reduce noise in post processing.

Fully Automatic

The last automatic option, fully automatic (P or Auto) may be your go-to choice if all of this still sounds too complicated.  Although the manual of higher-end DLSR cameras refer to this mode as “point and shoot”, don’t be ashamed to use this mode.  Sometime you will be in situation that is so dynamic and changing that you will want to concentrate more on composition and image capture and less on the nuances of your cameras settings.  In these cases, let your camera do more of the "thinking".  This mode works best in well-lit situations.  Develop the good habit of always noticing your aperture and shutter speed in the viewfinder—this will help you ensure that your camera is making choices that are suitable to your situation. 

Summary and Personal Preference

As you are planning your photography, you should consider how best to translate the impact of your observations and feeling to the camera’s sensor.  Knowing that the camera has the three parameters of the exposure triangle, and knowing how each of them affects or influences the final image’s characteristics, will allow you to make the “right” choice of  mode—for you, and for your situation.  Automatic modes are designed to help simplify your camera’s use…which mode you choose will help you get your exposure settings more quickly based on your priorities.

Personally, I like to start by having my ISO set on automatic.  It stays at 100 (or 200 for some cameras) and will only go higher when there is not enough light hitting the sensor based on my choice of aperture and shutter speed.  I can decide to control aperture (aperture priority) or the shutter speed (shutter priority)—and I’ll know when I do that, that two out of the three parameters will be automatically determined for me—giving me greater freedom to be creative and less focused on camera settings. 

Much of the decision making on mode choice is personal, and you may have different ideas on your approach…if that’s the case, I’d love to hear from you.  Email me at CostaMesaPhotography@gmail.com