Mountain Run - Jasper National Park, Alberta
You’ve gotten a bit more experienced and are now interested in some of the finer points of exposure. As I said in the introductory article on exposure, there are three major elements you need to control in order to have a proper exposure. The first two are aperture, and ISO. The aperture is the size of the iris that lets light into your sensor or film. It’s something you set on your lens. The effect of changing ISO is a little less obvious. This is all about choosing an ISO that’s compatible with all your other factors that will still allow you to make an image that’s worth keeping. A higher ISO means less quality imagery. Without getting into to much detail on that we’ll leave it there. For now, just know we’ll talk about aperture and ISO in more detail later. Today’s article is all about Shutter Speed, the third parameter for making proper exposures.
Shutter speed is one of the three basic settings you have control over to set proper exposure--shutter speed, aperture, and ISO.
Let me introduce a new concept, Exposure Value, or EV. Exposure Value is a single number representing the magnitude of the light falling on your subject and it’s a function of ISO--i.e. the EV number changes when you change the ISO or sensitivity of your sensor. A small number means less light. A bigger number means more light. As a result, a higher or lower EV points you to changing the camera’s aperture or shutter speed setting to make your camera take great photographs.
All things being equal, if you have a certain amount of light on your subject, you have a certain Exposure Value, or EV. With this EV being dependent on how sensitive your sensor is, you either set the camera’s aperture or shutter speed. Assuming the aperture is fixed, you can only adjust the shutter speed faster or slower to either allow more or less light in. It’s a pretty simple concept. A longer exposure will let more light in. A shorter exposure will let less light in.
Let’s go through some examples. Per the introduction article, the sunny-16 rule of thumb says at broad daylight with no clouds, the proper camera settings are ISO 100, f/16 and 1/100th sec shutter. If the ISO is twice as sensitive, then the shutter speed needs to be twice as fast, ISO 200, shutter speed 1/200th sec. The same goes the other way. If the ISO is 50 then the shutter speed needs to be 1/50th sec--i.e. twice as long. It’s all pretty simple stuff.
So, you can imagine if you’re shooting long exposures and decided a 30 sec exposure at f/4 was good for ISO 3200... Then at ISO 400, the shutter speed should be what? ISO is 1/8th as sensitive then the shutter speed needs to be eight times as long, or four minutes.
Conceptually, this is all pretty easy stuff and not very difficult to understand. So, you’re wondering to yourself why should the shutter speed matter that much? Well, it matters a lot. It matters mostly if there’s anything that moves. If everything you’re shooting isn’t moving or you aren’t moving, then shutter speed doesn’t matter very much. If what you’re shooting is moving and/or you’re hand holding your gear... then shutter speed means a lot. That’s what we’re getting into now.
When You’re Moving
One of the problems in photography is there’s no free lunch. Okay, this statement isn’t exclusive to photography but it’s certainly useful here. When the light is dark and you can’t change your aperture or ISO, you need to lower your shutter speed. The first thing you should be worried about is camera shake. You can write whole articles just on this subject. What this means is just the action of your holding or even touching your gear will cause some sort of camera shake. With shake comes vibration. With vibration comes movement which is the bane of all super-sharp photographs. Unless you’re trying something special, typically most photographers try to minimize camera shake as much as possible. What does this mean? It can mean using a tripod.
With a tripod, you can setup your gear, not touch anything, shoot the picture, and minimize camera shake due to you. This works great if you’re a landscape photographer and not moving around very much. This technique isn’t very useful if you’re a photojournalist that’s moving around a lot. In this active situation, you need to hold your gear as steady as possible. I’m not going to get into the basic of proper hand-holding technique. But, I will say there is a rule-of-thumb for the minimum shutter speed you should allow if you’re exercising good hand holding technique. The rule of thumb is 1/the focal length of your lens is your lowest hand holding shutter speed. This means the longer your lens is the higher your min-shutter speed should be. The min speed for a 50mm lens should be 1/50sec. For a 200mm lens... It should be 1/200sec. For a 21mm lens, the min speed is 1/20sec. As it said, it’s a rule-of-thumb and it’s useful when you’re already exercising good hand holding technique.
The way you apply this technique is just before pressing the shutter is check the shutter speed. If it’s higher than the focal length of the lens, you should be pretty confident you won’t have blurries due to “shakes”. If it’s less, then you need to do something. You either need to raise the shutter speed by adjusting one of the two other parameters--i.e aperture or image quality--or you need to steady yourself somehow. It completely depends on the situation on which thing you’re going to change, shutter speed or steady yourself.
What if you’re using a long lens and you’re using a tripod? Aren’t there camera shake issues there? Yes there are. They aren’t as obvious but they’re there. The first thing you need to do is read my article on long lens technique. From that article you can get a flavor for how things change when you’re using a really long lens.
By-the-way, there’s technology out there to help us out. It’s called Image Stabilization or Vibration Reduction. The idea here is your lens or camera will sense the camera’s shake and move the lens or sensor around to compensate for the vibration. Essentially, it’s compensating for your weaknesses and helping you out. How well does this stuff work? It’s fantastic. A few years ago, lots and lots of Nikon faithful jumped ship because Nikon was slow in introducing long lenses with this technology. Canon had it for years before Nikon had it in any meaningful numbers. They claim, the 1/the focal length rule of thumb hand holding could be improved by two or even three stops. Where previously you needed to hold your camera at 1/200sec, you could get by with 1/50sec with a two-stop improvement. For a three-stop improvment, the number drops to 1/25sec. Comparing 1/25sec to 1/200sec... That’s incredible. Tell me there aren’t people out there interested in that kind of technology. I certainly was.
The moral of this story is if you’re moving around, you need to consider what shutter speed you’re setting to make sure you aren’t accidentally introducing blurriness to your images.
What if your subject is moving?
What about if your subject is moving? No amount of handholding technique will make your subject sharp. No amount of Image Stabilization or Vibration Reduction technology will help. Assuming you have all your other problems taken care of, what do you do to compensate for your subject? That’s a really subjective statement. Obviously, the less your subject is moving the slower shutter speed you’ll be allowed. A completely stationary subject will only be limited by your minimum speed as noted above. What if the subject is moving fast--i.e running--and you want him to be tack sharp? You need a really fast shutter speed. How fast... it completely depends.
I use as a rule of thumb for large mammals if I set 1/200sec for a trotting or slower subject, he’ll be pretty sharp. At least everything except for the tips of his hooves. How do I improve my chances? I pan to keep my camera motion as consistent with my subject as possible. This means I pan, I shoot, and keep panning. That way, if any of the subject’s toes or hooves are moving too fast, I can make sure his eye is sharp. That’s the most important. Being smooth and consistent is important. Being jerky isn’t.
Eventually, I get to a point where I can’t keep the subject sharp no matter what I do because it’s too dark or the subject is moving too fast. Then I change my mindset and move to making pan shots. I wrote a whole article on this subject here? The point here is many photographers have it in their minds the only way to make worthwhile imagery is it has to be tack-sharp from end to end. I disagree. When the world doesn’t allow you enough light to keep image quality high and the aperture the way you want it, you need to concede something. That means you have to go with a slower shutter speed. Instead of trying to fake a sharp image, try to embrace your circumstances and shooting something different like a pan-blur as I note above. In these cases you can set your shutter speed much slower than needed to keep the subject sharp and only have to depend on your panning technique and a little bit of lady luck to get good images. There’s lot of potential here. Instead of packing up because the sun is setting, try pan shots with slower shutter speeds to make entirely different types of imagery.
What about if your subject is a bird? What do you do to keep him sharp? It depends on what you’re going for. If you’re only looking for the head or even the body to be sharp, you can easily get by with 1/500sec. If you’re hoping for sharp wings? You need a lot more. You need 1/800sec for large birds such as Sandhill Cranes, or even 1/1500sec for smaller sparrow type of birds. For freezing humming bird wings? That’s an entirely different subject I won’t discuss here.
In The End
There you have it. These are the basic considerations about shutter speed and exposure. Of course, I didn’t cover everything which is part of the appeal of photography. There’s so much self-discovery in photography. This is a good start and I hope you learned something.
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