histogram and exposure

Yougeshnee

I am presently doing an assignment that requires me to correctly expose and photograph a landscape referring to my cameras histogram, and then to underexpose by 2 stops and overexpose by two stops. Please advise on how to find my cameras histogram an how do I go about changing the stops. Very new to photography.

szlaszlo07

To enable histogram go to menu (by pressing the menu button), playback menu, playback display options, overview, then hit OK, then move up to done and hit ok. After that in playback mode, you have to push the up arrow when you preview an image. This will show you the histogram.
For a landscape picture select A mode (aperture priority), select f/8 or f/11 for aperture value by rotating the command dial. You can change the exposure by pressing and holding the exposure compensation button just behind the shutter button at the top of your camera. At the same time rotate the command dial until it shows -2/+2, and take the pictures.
Another way to take two pictures with different exposures is to use exposure bracketing. Press the I button, then move down to the lower right corner of your LCD screen to BKT OFF. Hit OK, and select AE2.0. Shoot at three times. This way the camera takes three pictures, one with the right exposure, one with 2 stops underexposed and one with 2 stops overexposed.
Hope this will help!

Geegee

How do I view the histogram for a picture that I am about to take?

bruto

You can only view the histogram for a picture that is completed.

To do this exercise correctly you must make sure that your camera is not set for "auto ISO" or the auto exposure will compensate for your change of stops. Go to the menu and disable Auto ISO. You can then choose a manual ISO speed. Stick to relatively low ISO, 100 to 400 for now.

Your best bet here is to set the camera to manual mode. The internal meter will be operating still. To get a correct exposure according to the meter, look at the bar graph in the rear display or the similar bar graph in the viewfinder, and adjust until no bars are showing to either side of the zero. You adjust shutter speed with the control wheel, and aperture with the control wheel and "+/-" exposure compensation button.

Proper exposure is achieved by combining shutter speed, aperture, and ISO speed correctly. The camera's sensor does not care whether you put a lot of light in slowly, or a little light in fast, (correction, I put it backwards, a lot of light fast or a little light slowly!) so you can get a proper exposure from a variety of different combinations of speed and aperture.

Each "stop" of exposure represents a doubling or a halving of the light hitting the sensor (approximately). Thus, changing shutter speed from 1/60 to 1/125 will reduce exposure by one stop. Changing the ISO from 100 to 200 will increase exposure by one stop. Changing the aperture from f/8 to f/11 will decrease exposure by one stop. Aperture numbers are not as easy to understand, being based on a complex formula in which the smallest number is largest, but the progression of traditional full stops is 1.4 - 2 - 2.8 - 4 -5.6 - 8 -11 -16 -22 - 32, with 1.4 the largest (most wide open).

You can change stops by several methods here. The camera's shutter and aperture controls operate by 1/3 stops per click. To overexpose by two stops, you can slow down the shutter speed by 6 clicks, or enlarge the aperture (go to a smaller f-stop) by six clicks. Reverse that process to underexpose. You can do this in any combination. You could change the aperture by one stop and the shutter speed by one stop, for a total of two. Alternatively, you can keep the settings the same, and change the ISO by two full speeds. On the D3200 each aperture (sorry, sloppy typing again, I meant each ISO speed!) speed is a full stop, and I imagine this is the same for the D5100.

Your camera's display will show two sets of histograms; one is divided into colors, and the other (the one you will want) is a white one which combines all color information into a single graph.

The histogram is a graph of what light has hit the sensor, with the darkest at the left, the brightest at the right and gray in the middle. A histogram of a properly exposed picture will show all its content between the right and left ends. Depending on various issues of what colors and proportions are in the picture, the graph may be very uneven in that space with peaks and valleys, but it is a good histogram if at least some content shows all the way across without touching either end. If it is overexposed, you will see that it crowds the right side of the graph and leaves empty space at the left. If it pushes at the right end, it will clip the highlights and blow out whites. If areas that should be at the black end are in the middle, they will look gray. If it is underexposed, it will crowd the left end, dark areas will be black, with loss of detail in the shadows and whites will be gray.

To get an idea of what is normal, you can set your camera to Aperture priority and make some pictures that look good. Check the histograms of pictures that look good, and you will get an initial idea of what you are aiming for; it will then be much easier to understand the histogram of a picture that is not good. Note how when all is working right, the meter will almost always spread the information over nearly the whole length of the histogram, stopping just short of the right end where highlights are blown and information lost.