The basic exposure thread

[Marko]

Hi Members,

I wanted to put out a thread to explain basic exposure and have people give their own input as well. Basic exposure is a stumbling block for newbies; one that they must understand in order to progress.

I'm copying and pasting some stuff from previous threads and members should feel free to do the same. When it comes to basic exposure DO NOT USE FLASH WHEN YOU ARE LEARNING. Flash is a level 2 element turn it off. YOU MUST fully understand basic exposure before adding a new variable.

Here are some notes on basic exposure.

All a camera is, is hole with a flap over it. When the flap is lifted light hits film or a sensor. On modern cameras, depending on the setting you use, the camera's meter suggests an exposure. This suggestion is good one in the following condition;

- When there is a good representation of light and dark tones. This is called a normal scene

AT THIS POINT WE MUST SAY THAT THE CAMERA IS BLIND. IT DOES NOT KNOW WHAT IT IS LOOKING AT BECAUSE IT HAS NO BRAIN. ALL IT DOES IS AVERAGE OUT THE TONES IT SEES AND SPITS OUT AN EXPOSURE. ALTHOUGH THIS IS NOT INTUITIVE (FOR COLOUR PHOTOGRAPHY) THE COLOUR MID-GREY IS THAT MIDDLE TONE THAT THE CAMERA USES AS THE AVERAGE.

This example below is perfect.

This is an image of snow by casil403 (thx in advance:))
Snow is white but this shot is grey - BECAUSE THE CAMERA IS BLIND. It has no idea what it is looking at so it averages out the white snow and turns it grey.
There is only white in the scene, so it is NOT normal.
Therefore if you use the meter's reading in this case you will NEVER EVER get white snow. You have to make adjustments to the meter's reading.

That's the end of the first note - More to come.
Thx - marko

[Gem]

http://www.freesmileys.org/smileys/smiley-forum/nicethread.gif (http://www.freesmileys.org)

[casil403]

Boy do Ineed this thread...YaY! :highfive:

[Mad Aussie]

The way I look at it is this ...

What the Camera Sees ...
Instead of thinking about how I see the scene ... I imagine what the camera sees.

A camera doesn't have an iris and brain that can adjust to different brightness and darkness in a scene many many times a second.
It looks at a scene ... sees a certain level of brightness (or lack of) entering the sensor via the lens, and makes a call on what settings it needs to record the average that Marko spoke about above.
Therefore, in every case where a camera is left to make the decisions, only the elements in the scene with the average brightness level the camera saw will be properly exposed.

So, when a camera looks at a scene that's predominantly snow, as in the images above, it's sees a very bright, overall level and exposes for that by darkening the image via aperture or shutter speeds etc depending on your mode you are using.

What to do?
If you look at the scene and are sure the camera is going to think it's too bright and ignore the darker elements then you have to anticipate that and counter act.
If you are using a mode like Shutter Priority or Aperture Priority then you can adjust the Exposure Compensation.
The trick is remembering which way to go.
By remembering how the camera sees the scene AND what it will do about it (in this case it will darken the snow) it becomes easy. For the snow you would ADD Exposure Compensation to counter act the darkening the camera will do.
If the scene was a black dog on tarmac you know the camera will see a dark scene and try to lighten the image therefore making the blacks look washed out. You would go the opposite way and decrease the Exposure Compensation.

However, using Manual Mode you can take a few photos and experiment with the various light controlling options you have (shutter speed, aperture and ISO) until you get the best image.

In all these modes you can also use Exposure Bracketing to force the camera to take two other shots at different exposures after it chooses the one it thought was best.

Confused by HDR?
When the levels of brightness and darkness are too much we call this a High Dynamic Range (HDR).

One of the most effective ways to take a scene with a high dynamic range is to take several photos and blend them together in post processing. This allows you to adjust the dark areas separate from the light areas.
Using layers and layer masking is an effective to get the image to look more natural to what your smart iris and brain saw for you rather than what the poor camera came up with.
These days we tend to refer to this process as 'making a composite' but it IS a technique of HDR.
Recently though, the term 'HDR' when applied to an image is referring to software such as Photomatix that has the ability to not only make the scene look more natural but also over exaggerate it in a way that is becoming more and more acceptable as people find amazing ways to use this technique.
And example is z09_jim's efforts here http://www.photography.ca/Forums/showthread.php?t=2435
And for more HDR's of a more natural look again we'll use z09_jim's work here http://www.photography.ca/Forums/showthread.php?t=2556

Hope that helps a little http://www.mtbdirt.com.au/home/smf/Smileys/classic/searchme.gif

[Mad Aussie]

I thought I might add that some people see HDR techniques as cheating but HDR has been around for the long time.
I read somewhere that it actually started in the film industry but I've heard Ansell Adams being credited with using the technique for his b&W images.
It was difficult process back then of course, multiple shots on negative and having to splice out the overexposed sections of one negative and lay it over another that had better exposure in the bright bits etc.
Even things like dodging and burning were done chemically many years ago before digital photography was thought of I believe.

I was never into processing my own negatives so I'm quite naive on this really.