Now the outside detail can be seen but the inside has become totally black with no detail. Once again capturing detail inside and outside at the same time is beyond the dynamic range of the sensor – you have to choose what you want to have correctly exposed because what you can capture, all in one exposure, is limited by the dynamic range of the sensor.
Try this: Set your camera to spot metering and find a scene like this – bright window and dark room. Turn off auto ISO, use ‘A’ mode or ‘Aperture priority’ and take a photo with the window in the centre of the frame – spot metering is only seeing the light outside. Now take another picture with the window to the side and the centre focus point of your camera on the wall inside. You will see a vast difference in the exposure – in one image the light outside the window will look right while the wall inside is close to being black, and in the other image the wall will look right while the window is white.
Now when we compare these images how much difference is there between the shutter speeds chosen by the camera? Well compare 1/5th sec to 1/250th sec. 250 divided by 5 = 50. The light outside is 50 times brighter than inside! Of course depending on conditions where you are there will be variations in this experiment so don’t think there is something wrong if you don’t see a difference of 50 X .
The initial image in this chapter is the result of combining the two images in Photoshop – it’s not nice to have to resort to editing images to get what you want but sometimes it is unavoidable. This combining of the two images results in a rather crude ‘High Dynamic Range’ or ‘HDR’ image.
Another solution would be to use flash to light up the inside of the house while exposing correctly for the outside light.
So what about an image where the light is even enough not to have to do this and what does the camera’s metering system aim to achieve to obtain ‘correct’ exposure?
Try this: put your camera in ‘P’ mode. Use centre weighted or matrix/pattern metering mode and take a picture of something in an even lighting arrangement – perhaps a dull color or simply a patch of grass or blue sky with nothing else in the image. Now check your histogram.
Side note: If anyone asks why you are using Program mode tell them ‘P’ stands for ‘Professional’ but if you reach the stage where you don’t need to use it then you tell them ‘P’ stands for ‘Panic’ because it tries to do everything for you besides turn on the flash. (That’s why it’s best to stay away from the fully automatic modes because you never know when it will pop the flash up when you don’t want it to.)
With an even patch of dark blue sky the histogram should look something like this: Very low contrast, because there is very little difference in the tones of the scene.