Category:Photography Basics
From ReefPedia
Understanding exposure
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It’s all about the light.
The word photography, broken down to its basics, means the art of recording light. Whoever named it photography couldn’t have said it better. The first and most important concept for you to grasp is that in photography, everything is ruled by light. Specifically, how much or how little of it is present in the photo you want to take.
The amount of light available determines how you’ll be able to take your photograph. Outside in broad daylight, your options are nearly unlimited. Indoors and under low light, however, you have much less leeway and an understanding of exposure becomes incredibly important to successful photography.
Simply put, The more light, the better.
STOPS
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Shutter speed and aperture
Point your camera at your tank and press the shutter release halfway down. You should see a reading on the screen, such as “1/60 5.6”. These numbers are your shutter speed and aperture, respectively, and they are the building blocks of exposure.
Shutter Speed
Shutter speed is the amount of time the shutters are open exposing your photograph. So at 1/4 second, the shutters are taking in everything in front of the lens for a quarter of a second.
Let’s say you’re pointing the camera at a moving fish for that quarter of a second. Because the fish moves during that quarter of a second, it will come out on the photo as a blur. Taken at 1/200 of a second, unless the fish was being chased by a shark, it probably didn’t move quickly enough in 1/200 of a second to become blurred in the photo.
Now, let’s say your shutter speed again is 1/4. You hold the camera to the tank, frame a nice picture of a coral, push the shutter button, and 1/4 second later you’re graced with another blurry photo- this time of a non-moving coral. What happened? Your hands moved during that 1/4 second, that’s what. Not even a surgeon can take great handheld photos at 1/4 of a second. We all move a little, and at slow shutter speeds, that little is enough to ruin the picture.
Stops = increments
Now, again, let’s say our shutter speed is 1/200. Barring those mornings when five cups of coffee just isn’t enough, you should get a rather crisp, un-blurry handheld shot of your coral at 1/200.
You can see where this is going. When it comes to shutter speed, the faster the better.
Aperture
For every Yin there is a yang. And so, shutter speed’s opposite and companion, its partner in crime, is aperture.
Aperture is the opening in the lens through which the image is captured. Also called f-stop, aperture is usually expressed after shutter speed as a number, often with an “f” in front of it. So if your camera reads 1/60 f/5.6, your shutter speed is 1/60 and your aperture is f/5.6.
Changing your aperture changes your depth-of-field, the amount of the photo that will be in focus from front to back.
Let’s say you shoot a coral at F/2.8, again at f/8 and then again at f/16. At f/2.8, the part of the coral closest to you may be in focus but even the back of the coral is blurred. At f/8, the entire coral may be in sharp focus but the rockwork behind it is not. At f/16, the entire coral and rockwork are in focus.
So, the higher the f-stop, the better. Right? Not so fast.
Shutter speed and aperture together.
Here’s the rub. The higher your f-stop setting (and therefore the greater your depth-of-field), the slower your shutter speed. Matter of fact, for every notch you bump up the aperture, your shutter speed is cut in half.
So at f/2.8, let’s say you’ve got a shutter speed of 1/60. But you want that whole coral in view, so you bump up the aperture three notches to f/8. Your resulting shutter speed is 1/8 of a second. Hope you’ve got that tripod handy. Now let’s say you want that rockwork in focus too, so you go up two more notches to f/16. Your shutter speed is now 1/2 second. Better have that tripod handy and hope the coral isn’t moving.
Lost yet? Don’t be discouraged. Exposure is one of the most important aspects of photography but it’s also one of the most difficult to grasp. I had to read a chapter on exposure several times, then go play with the camera repeatedly, to finally understand the inverse relationship between shutter speed and aperture. Once I did, everything about photography got a whole lot easier. Get this down and the rest will be much easier. I promise.
The light meter
So what evil little critter living inside your camera decides that you can’t shoot at 1/200 and f/16? It’s called the light meter. Ahh, back to light. Remember that it’s the most important thing in photography? Now you know why. The more light that’s available, the faster your shutter speed can be at any given aperture.
In the aquarium environment, the most important thing to know is how completely and totally at the mercy of light levels we really are. And in the aquarium environment, there isn’t much to work with. Which is why so many people have so many problems photographing aquaria. Without an understanding of the importance of light and the acceptance that it’s a challenge to work through using certain techniques, we’re doomed to keep pressing the button until we get somewhat lucky.
ISO saves the day
Well, not necessarily. But it can be a big help. ISO, in terms of digital cameras, is the sensitivity of the camera’s digital sensor. The numeric system comes from the film world, where ISO speed is a measurement of the sensitivity of the film.
The higher the number, the more sensitive the sensor is – and therefore, the less time it needs for a proper exposure. So, just as raising the f-stop will cause the shutter speed to be cut in half, raising the ISO level from 100 to 200 will double the shutter speed.
But, again, there’s a rub. As we make the sensor work harder, we get more artifacts and graininess in our photos- in the digital world, called noise. So, ISO allows us to bump up the shutter speed at the expense of image quality.
Fortunately, great strides are being made in digital sensors and the noise issue is becoming less and less pronounced. At ISO 400, my first digicam’s output was, to me, unbearably noisy. At 400, my current camera produces excellent results under most circumstances. As manufacturers develop better sensors, I see noise handling ability surpassing the number of megapixels as the number one selling point. This is one area where the digital SLR is leading the pack by a wide margin.
Flash
You may ask yourself, “If light is so important, and we desperately need it, why don’t I just use the handy-dandy little flash they built into my camera?”
Because that flash, more than likely, sucks. A good flash is a great solution to the light problem. But a bad flash is a terrible solution. And in 99% of cases, including those expensive Digital SLR cameras, the built-in flash comes nowhere near acceptable for aquarium photography. They’re too weak, they’re too close to the lens so you’ll get glare on the glass, and often they’ll make everything look just plain awful with harsh and poorly-colored lighting.
Fortunately, most digicams these days are compatible with off-camera flash units, many of which are excellent. If your camera is one of them, a good flash would be a wise investment indeed. If your camera isn’t one of them, skip to the next section. The rest of this one will just make you jealous.
Exposure compensation
Exposure Compensation is your way of wrestling a little control back from the light meter.
Your camera’s meter isn’t perfect. And it can be fooled. If your pictures are coming out darker than you’d like, consult your manual and apply a bit of positive exposure compensation. If there are bright areas in the photo with no detail, apply some negative exposure compensation. Dynamic range and the digital processor Metering modes The light meter normally takes a reading and calculates how much light is available when you point your camera at the subject. Most cameras will have a few different metering options- typically matrix, center-weighted and spot metering. The metering mode will determine how much of the image in the viewfinder is taken into consideration when metering. Most of the time, you’re better off in matrix mode, where the camera usually does some fancy calculations and generally gets pretty close to right-on.
Center-weighted metering will put more emphasis on the area in the middle of the viewfinder when calculating exposure.
Spot metering will place all the emphasis right there, in the middle.
If you thin k a light source is skewing your exposure, or you want to really bring out your subject at the cost of over-or-underexposing your background, give one of these modes a try. I find I’m normally better off keeping it in matrix mode. AE lock and focus lock
Bracketing
Here’s some of the best advice and one of the most useful techniques I can give you. And frankly, I think it’s an underused technique in aquarium photography.
Bracketing means taking a series of photos, slightly changing one setting in each while the others remain constant.
For example, let’s say your shot is coming out a little too bright. You know by now that the way to correct this is by using some exposure compensation. But how much? Bracketing will allow you to simultaneously find out and cover your hiney that you got the shot. Take one shot without exposure compensation. Then another at, say, -1/3. Another at –2/3, and then another at –1. You have now bracketed four shots, one of which is most likely dead on. Figure out which one you like best, trash the other three, and make a mental note of the amount of negative exposure compensation that worked. With experience, you won’t need to bracket in that situation anymore. You’ll just know by looking at the photo that it needs, for example, -2/3 exposure compensation.
The same can be done with shutter speed, aperture is especially handy, white balance settings, zoom range, manual focus, and just about any other variable you can think of.
Remember, it’s digital. Go ahead and waste several shots to get one good one. Drag the bad ones to the trash can- they did their job.
Shooting modes
That dial on the camera can be a scary thing. All those letters representing modes you don’t understand. Well, the good news is, once you understand the basics of exposure those modes will come in quite handy.
In “Auto” mode, your camera picks a shutter speed and aperture. That’s what you get, let’s press the button and go. No control for you.
That’s where the other modes come in. Namely, shutter priority, aperture priority, and manual modes.
When you choose one of the elements of exposure, you decide where the perfect compromise lies between shutter speed and aperture. This is accomplished with shutter priority and aperture priority modes.
Let’s start with aperture priority, because that’s what I prefer to shoot in and, well, it’s my book. Switch from that comfy auto mode into aperture-priority and you gain a whole new level of control over your photographs. Sadly, the light meter still determines what’s possible. But within those boundaries, you choose the aperture and the camera will change the shutter speed to match it. If you want more depth-of-field, dial up a higher f-stop and you’ll watch the shutter speed get slower along with it. If you decide you can deal with a little less depth-of-field in return for more speed, dial in a lower f-stop setting and the shutter speed will get faster.
Now switch to shutter priority mode. It works just like aperture priority, except you pick the shutter speed and the camera will pick the aperture.
It’s tough to go wrong in either of these modes. When you begin consciously deciding how much depth of field and shutter speed to use, you instantly move past the person taking snapshots and become a photographer.
Try out both modes. See which one feels right to you. It doesn’t matter which one you choose, so pick the one you like best and forget that silly auto mode ever existed.
Manual mode is not for the faint of heart. In manual mode, you choose both the shutter speed and aperture. This means you can instantly take that light meter that’s been ruining all the fun and turn it from the savage dictator into a nagging mother-in-law. Instead of stopping you from taking a low-light picture at 1/500 @ f/16, it’ll just make the display blink or flash, or an icon pop up in your display (depending on your camera) telling you it’s not a good idea. Go ahead, defy that nagging old light meter. You know you want to, and now you can. What do you get when you push the button? Something that resembles the inside of your eyelids. Blackness. You’ve grossly underexposed the photo, and that light meter just sat there and let you do it. It’ll let you overexpose the photo too. It’s great for experimenting, but in general, you’re better off shooting in either aperture priority or shutter-priority modes and using exposure compensation where needed.
