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Too dark...too bright....

Too dark or too bright.....this is due to poor exposure of the sensor to light. Is it a problem if my photo is too dark or too bright? May be yes and may be no, depends on what you want in your image. If the photo is too dark (underexposed), you will loss the detail of the shadow. If the photo is too bright (overexposed), you will loss the texture of the cloud and sky.

Exposure is a combination of two fundamental settings: the aperture opening and the shutter speed. Aperture opening is the function in your lens and the shutter speed is the function in your camera. Optimal exposure can be achieved with many combinations of aperture opening size and the shutter speed, BUT each combination will have differences in depth of focus, motion blur and etc. How this exposure can be controlled? The answer is by having a good understanding of the combination of aperture and shutter speed.

Shallow depth of focus, focus point was on the middle broccoli, focal length of 50 mm,
large aperture opening of f1.8,  shutter speed at 1/200s
The opening of aperture can be very wide (small f-number) or very narrow (large f-number). Each lens have specific range of f-numbers. Typical values are f1.8, 2, 2.8, 3.5, 4, 5.6, 8, 11, 16, 22 and 32. Each f-number increment (also known as f-stop) will reduce by halve the amount of light enters the camera. Let say your lens has a mark of 18 - 55mm 1 : 3.5 - 5.6, this means that at 18 mm of focal length the larger opening will be f3.5, , and at 55 mm of focal length the larger opening will be f5.6. Smaller f-number will have a shallow depth of focus which is very useful in portrait or food. Larger f-number will have a broad depth of focus which is very useful in landscape or architectural photography.

Shutter speed is the length of time at which the sensor is exposed to light. The shutter speeds can range from very FAST (1/1000 second) to very slow (several second). Faster shutter speed makes all moving objects look static. On the other hand, very slow shutter speed makes all moving objects look blurry. Capturing image with slow shutter speed usually requires tripod. Image stabilizer (IS) or Vibration reduction (VR) may allow hand-held photography with a shutter speed as low as 1/30 second.

Broad depth of field, focal length of 70mm, focus at infinity, shutter speed at 1 second, narrow aperture opening at f11
How you know that you have reach the optimal exposure? This is easy with DSLR, look at the exposure meter (which has a negative and positive extreme marks), the exposure mark should be in the middle of these extreme marks. This is only important when your camera was set at manual mode. If you set your camera at aperture (Av for Canon or A for Nikon) as priority, you just have to fix the f-number and the camera will look for the best shutter speed. If you set your camera at shutter speed (Tv for Canon or S for Nikon) as priority, you just have to fix the shutter speed and the camera will look for the best aperture opening. Basically, if the aperture opening is very narrow (big f-number), the shutter speed will become very slow, and vice versa. In both conditions, if the optimal exposure cannot be achieved, try to change your ISO value or set the ISO to auto. Larger ISO value makes the camera sensor much more sensitive however, the image will be much grainier. This makes the image less sharp. Try some experiments with difference combinations of f-numbers and shutter speeds on one particular object and landscape. See the results and you will understand better. Good luck.

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