What auto mode lacks in intelligence, it makes up for in speed. If your ability to produce well exposed images doesn’t need a high level of accuracy, than the benefits of auto mode (the camera doing all the thinking) may be attractive.
Don’t get me wrong, the modern DSLR is a highly accurately calculating piece of technology, and its abilities are amazing. The problem isn’t how accurate it is, it’s what it chooses to be accurate about that can’t be counted on.
Thankfully, manufacturers offer us different exposure modes that allow us to tell our cameras what part of the thinking about the exposure that they’re allowed to do.
The two modes that are here to rescue us from the slow nature of shooting manual mode are shutter priority (labeled Tv on Canon or S on Nikon) and aperture priority (labeled Av on Canon or A on Nikon). I’ll be henceforth referring to the modes in the form of the Canon abbreviations with the Nikon in parenthesis.
Viewing the chart below will emphasize the differences in the modes for you very quickly.
These modes allow either shutter or aperture to be selected by the camera.
So how are these any different than auto? What would a situation have to be where I would allow my camera’s best guess to suffice? The answers to these questions are: when I already know what it will choose and/or when what it chooses doesn’t matter.
Here is an example for each mode. Picture yourself at a wedding in a poorly lit (read: typical) church. You know you need a certain shutter speed so you don’t get a bad case of the blurs when the bride processes down the aisle, but you’ve run late and don’t have time to figure out your manual settings. Throwing it in Tv (S) and setting your shutter speed to 1/160 will ensure that you can stop the motion of the average walking person. Here’s what you can expect. Since the church is dark, you can count on the camera to open the aperture as wide as it will allow. This scenario gives you the mentality of manual – knowing what all your settings will be because of your environment – with the speed of letting the camera do some of the thinking. In this case, you can expect the camera to perform a certain way because of the darkness.
Envision the same scenario outside at a soccer game on a clear day. You might set your shutter speed to 1/500 or higher because you want to stop the action of someone running. At this time, unless you have a need for a specific kind of depth of field, what the camera chooses doesn’t much matter because light is not at a premium. In this case, it doesn’t matter (in terms of exposure) what the camera chooses because there is plenty of light to get the shutter speed you need.
With aperture priority, situations can be similar.
Imagine yourself a landscape photographer who uses a tripod to ensure maximum stability and accurate horizon lines. Let’s say it’s 30 minutes after sunset – still bright enough to see color in the sky, but not to hand hold a camera. You want the maximum depth of field to get both foreground and background (mountains and such) in focus so you close down your aperture all the way to f22. In this case, you’re using a small aperture so you can expect that the camera will slow down your shutter speed, and since you’re using a tripod, how much it slows down doesn’t matter a great deal.
Lastly, say you’re taking a portrait of someone outdoors in the shade on a sunny day. Your priority may well be depth of field – it would be for me. Aperture priority is a good choice because you can select a wide aperture that will give you that great out of focus background (called bokeh) you desire. Because you are shooting someone who isn’t moving, the shutter speed the camera chooses will be more than enough to keep them from being blurry. In this case, you can expect the camera to raise your shutter speed, but since your subject is stationary, there is no consequence or change in appearance.
Even though these are hypothetical situations and I can imagine a few oblique “but ifs,” these are examples of cases when I trust my camera to make decisions and once more, it boils down to this: when I already know what it will choose, or when what it chooses doesn’t matter.
Personally, I don’t pick a favorite mode, I use whichever of these three modes best suits a particular situation or environment. To me, they have the potential to be equally valuable. That said, if you asked me for the breakdown of how often I’m actually using each of these modes, I would probably admit to using Tv (S) about 10% of the time I’m shooting, M about 35% of the time, with 55% spent in Av (A). Most of this estimation is vested in where I choose to shoot. If I were in a studio, I would shoot manual only. Since I generally plan to be shooting portraits on-location and in the shade, Av suits my needs pretty well the majority of the time.
This conversation on bokeh is a good opportunity to recall what I said earlier about where bokeh comes from. In a prior post on lenses, I mentioned that aperture is what controls depth of field. This is accurate but there is another variable one can manipulate to increase depth of field that doesn’t have anything to do with aperture, or your lens at all, which is why I didn’t find it fitting to include in that chapter.
If you change nothing else in how you frame a shot, your aperture is the only thing that will change your depth of field. What depth of field, and bokeh as a result, can be changed by otherwise is a subject’s relative distance to its background. This is good news for someone who has already invested in kit lenses with mediocre apertures because it means with a little know-how and creativity you can realize that you’re not banished from the beautiful world of bokeh.
Below, you will find a diagram with four cameras, labeled A, B, C, & D. The subject is represented by the green line and the background represented by the red line. The distance to the subject is represented by the orange underline and the distance from it to the background is represented by the blue underline. Assume that the aperture remains constant.
Let’s start with A&B. Which distance is greater in camera A? Distance to background. Which distance is greater in camera B? Distance to subject.
Camera B has very little distance between subject and background, therefore they are much closer to the same plane, and the focus of each of them will not vary much from one to the other. Camera A has a great distance between subject and background, and as a result, they are much further from being on the same plane, rendering them focused much differently.
In simple words, the farther away a background is from a subject, the more out of focus it will be (assuming you’ve focused on your subject).
Cameras C&D offer a different insight. They bring up the fact that the closer you get to your camera, the more depth of field changes.
Let’s put it this way, if you have two dollars to your name and someone takes one from you, is that a big change? Of course! On the other hand, if you have 100 dollars and someone takes 50 from you, you’ve still lost half your net worth, but you’ll probably survive.
Convert dollars to distance and the theory remains the same.
Even though camera D has a technically greater distance between the subject and the background than camera C, the depth of field will be far tighter in example C. This seems to deny what I just said about distance, but it’s not about strict distance, it’s about distance ratio. Earlier I said the subjects relative distance to the background. Relatively speaking, the distance between subject and background is much greater (say, 2:1) in C than it is in D (closer to 1:1). The less distance you have in total, the more each unit (millimeter, inch, foot) impacts depth of field.
Look past the sketch to the what’s important: the concept of relative distance is the key to depth of field with lenses that don’t offer much in that area because of aperture limitations.
In an earlier post, I mentioned the exposure meter inside the viewfinder of our cameras. While writing on exposure modes, I emphasized when you might want to let your camera decide to do some of the thinking for you. It is very important that what follows those concepts sheds light on what your camera is considering when it generates that meter, because that will impact what choices it makes in Av (A) or Tv (S) modes.
Metering is the process by which your camera estimates how much light is entering the lens. That readout, shown in section 3.1, behaves differently depending on what mode you are shooting in.
In M, the meter will read like a fortune teller of what kind of exposure your current settings will produce if you push the shutter. It changes based on what you’re pointing the camera at, and sets that information against your settings. To change it, either you have to change your settings or point it at something else. A meter reading left of center will look darker, right of center will look brighter.
In Av (A) and Tv (S), however, you can actually set the meter. It would have to be a special circumstance if you wanted to intentionally over or underexpose an image, most of the time we want rock solid centered meters.
What’s key to the accuracy of the graph in M or the accuracy of the choices the camera makes to honor the way you’ve set your meter in Av (A) and Tv (S), is what metering mode your camera is set to.
There are three main metering modes. I have seen others on certain models, but they basically break down in the following way.
The most common metering mode (meaning, your camera is set to this when you take it out of the box and almost nobody bothers to change it) takes into account an estimated average of how much light is coming into your whole frame. This metering mode is called Evaluative in Canon and Matrix in Nikon.
Much like auto exposure, this mode is not very useful in many situations because of how unspecific it is. There could be any number of things in your frame that you don’t care about how properly exposed they are.
Try taking a picture in a room with a view of a window on a sunny day. Either what’s outside will look far too bright and what’s inside will look decent, or what’s outside will look decent and what’s inside will look far too dark. Cameras just don’t have the dynamic range that human eyes do. But let’s say it’s a photo for a real estate listing – you may not give a rip about what’s outside if you’re taking a photo of a kitchen. A blown out (all white) window may even prove less distracting, which would be a plus.
No matter what you want, though, your camera won’t know what it is other than by guessing. This is why I find evaluative metering to be the most risky, or least useful of the modes. I have been known to use this mode, it’s nowhere near the evil green square, but it’s similar in the sense that I just don’t trust it to know what I’ll need.
The second metering mode is called center- weighted. This means that the camera will only consider a smaller portion in the center of your frame when it makes those decisions. This is better than using the whole frame, but it’s hard to know exactly how much is being taken into account when looking through the viewfinder, so although it might work for some situations, I don’t use this mode for that reason.
The third metering mode is spot metering, and I use it quite frequently. This mode is like a more specific version of center-weighted. Spot metering uses only a very minuscule portion of the center of your frame to gather the metering information. The shortcoming of spot metering, if you could call it that since it’s programmed that way, is that it is unlikely you will always want your main subject smack dab in the center of your frame. There’s a handy workaround for that very concern.
This mode can be very powerful when used in tandem with the Auto Exposure (AE) Lock feature in Av (A) or Tv (S). On your camera, the AE button looks like an asterisk, and in Av or Tv mode, it will allow you to lock in an exposure setting before taking a picture.
In spot metering mode, best practices are to point your center focus point at what you want exposed well (for me, it’s usually faces), push the AE lock button and then recompose the image before pushing the shutter release button (the one that takes the picture). It’s very easy to execute that process, it just takes a little bit of getting into the routine before the speed advantages are really reaped. And when they are, they are significant.
Moving on: The art of composition: “rules” of designing a shot
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