Exposure can be both a simple and complex subject. I’ll cover two topics in this post - a more detailed discussion about Correct exposure and the Give and Take of Photography.
In all the automatic modes, the camera’s firmware turns on the light meter, reads the light hitting the sensor, activates an algorithm, which sets the Shutter Speed, Aperture and ISO values and captures the image as you press the Shutter Release button. All this happens within milliseconds. What you see is an exposed image on your LCD screen that looks pretty good. Maybe.
In Manual Mode, you set the ISO value, adjust the Shutter Speed and Aperture, press the Shutter Release and view the image on the camera’s LCD screen.
If you’re happy with the result, then the exposure’s “correct”.
If you’re not happy with the image, you re-adjust either the Shutter Speed or Aperture value and capture another image. You repeat this procedure until you’re happy with the resulting image. it could take you 3 or 4 attempts. This is a trial and error approach.
As you can see, “correct” exposure is a creative, personal choice. “Correct” all depends on your personal choice. There is no set Shutter Speed or Aperture combination that gives you a “correct” image exposure for every image.
Shutter Speed and Aperture control exposure. But what about ISO you ask?
Briefly, ISO does not affect exposure. It also does not make the sensor more sensitive to light!! In a later post, I’ll discuss ISO in more detail.
In digital photography, exposure is the amount of light (Aperture) and the amount of time (Shutter Speed) it’s allowed to enter through the lens and reach the camera’s sensor.
The key take away here is there is no such thing as a “correct” exposure.
The Give and Take of Photography
What do I mean by Give-and-Take??
As discussed above, photographic exposure involves two camera settings: Shutter Speed and Aperture.
Shutter Speed’s give-and-take impacts the subject matter’s blurring. If your selected Shutter Speed is too slow, the resulting subject may be blurred where you wanted it crisp and sharp. On the other hand, if you want to blur the subject’s motion and the applicable Shutter Speed is too fast, the resultant image is crisp and sharp.
If you have to use a slow Shutter Speed due to a low light level and you’re shooting hand held, you may get a blurred image due to camera shake. (You forgot your tripod at home or you haven’t purchased one yet.)
If you’re using a very long telephoto lens, e.g., around 70mm or more, and shooting handheld, again you might end up with a blurred image due to camera shake if the Shutter Speed is too slow.
As you can see, there is no perfect Shutter Speed for every image. To obtain a sharp or blurred image all depends on a number of factors.
Aperture’s give-and-take impacts an image’s Depth-of-Field (DoF). A wide open Aperture renders a shallow DoF, while a small Aperture produces an image with great DoF.
The image on the left was shot at f 2.8, while the image on the right was shot at f 22.
A wide open Aperture, e.g., f 1.4, lets a lot of light in. A very small Aperture, e.g., f 22, reduces the amount of light a great deal. However, a small Aperture setting also introduces diffraction. Diffraction means the edges of your photograph grows progressively less sharp at smaller and smaller aperture values – f/16, f/22, and so on.
The following image shows two Aperture examples - the one on the left represents a wide Aperture setting, where as the one on the right represents a small Aperture setting. Notice the increased curve to the light as it enters the smaller Aperture setting. This is because light bends as it passes an edge. This can cause the edges of an image to be less sharp than the centre.
That completes this brief overview of exposure and the Give and Take of Photography.
If you have any specific questions, please email me at email@example.com. I’ll be happy to answer any questions and may include your question and answer in a future post.