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Member since: Tue Aug 7, 2012, 07:37 AM
Number of posts: 1,411

About Me

Photographer, chef, gardener, lover of the bizarre, liberal socialist democrat, humorist. Did I mention lover of the bizarre??

Journal Archives

Photography 101 ... Exposure and Metering Quirks

As the newbie as registered DUer, (long, long time lurker) I thought that since the photography group is my favorite place to post and read and visit after I scan the latest and greatest threads, I will periodically post little lessons for those interested in learning more about photography.

Most of the info I will post can most likely be found in that little manual that came with your camera ... but who reads that stuff, eh!? It can also be found all over the interwebs. But these little lessons will be coming at 'cha straight from a DUer. How great is that!?

I start with exposure and metering quirks ... one of my favorite subjects. The reason I am beginning with this is because cameras are stupid. Armed with a bit of knowledge, one can compensate for the camera's lack of reasoning and command it to do your bidding.

Let me begin. Ahem (clearing throat)

A camera on automatic setting wants to make every picture you take a perfect exposure. And this is great if what you are taking a picture of is of "average" exposure values. It's meter measures the light reflecting off your subject and adjusts itself so it is perfectly exposed .. not too light and not too dark. But problems will arise if the reflected light is really bright, an example being a sandy beach, a polar bear in a blizzard or your favorite bride, all dressed in white while standing in front of the white marble altar. It will also try to correct for really dark scenes or subjects, the classic example being the black cat in the coal bin.

Let's examine a very light subject.

I used these lovely white sea shells for this example. The camera see bunches of light coming in and says to itself, "Oh, I'm going to adjust my settings to take a perfect average picture". And this is what happens

The photo is under exposed. To the camera it is perfectly exposed. It measured the light coming in and made adjustments for an average amount of light. What the camera operator needs to do is say, "Bad camera!! It needs more light!" This is where you take over. If you have manual override you merely let more light enter the camera ... a slower shutter speed or a larger aperture (fstop). If your camera has picture modes search for the one that is for snow, or beach, or backlit, or something ... you may actually have to consult your manual for this info.

By changing my settings to allow more light into the camera a better approximation of actual scene is captured ...

The little graph in each picture is representative of how many pixels in the picture are in each tonal range ... darker pixels to the left side and lighter pixels to the left. As you can see in the top graph, everything is pushed to the dark side, Luke. In the second shot they are more evenly distributed with many more pixels in the lighter range. This is good.

The camera does the exact opposite with dark scenes and subjects. It thinks to itself, "Gee, there's not much light coming in so I better increase the exposure." The end results are an over exposed picture. We, the photographic geniuses, know that this is wrong. So we make the camera submit to our wishes and command it to cut back the exposure. A faster shutter speed, smaller aperture or some combo of both.

The overexposed dark subject

And the compensated, correct exposure

So keep in mind:
If the subject/scene is light, white, bright; don't let the camera underexpose the shot ... compensate by going manual and decrease shutter speed or use a larger aperture or a combination of both. No manual available ... check your camera's scene modes for beach, snow or backlit.

If the subject/scene is dark, black, spooky; the camera is going to overexpose. Compensate by going manual and increasing shutter speed, using a smaller aperture or a combo of both. No manual override check your scene modes for night scene, fireworks or black cat in a coal bin setting.

Remember, the camera is trying it's best but it has no idea what is correct for every subject unless you tell it. Left to it's own devices, it can and will disappoint at times.

The end.

(There will be a short quiz next week but it won't be graded)

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