One of the reasons I have found photographs come out different from how they appear through the viewfinder, is due to the way DSLRs operate.
When we adjust various settings on the DSLR to setup a shot, the lens DOES NOT adjust the aperture. The aperture is adjusted only when we finally fully press the shooting button.
And this is what creates a small problem. While looking through the viewfinder, we see a bright image. Then we click and preview it, only to find an image that is much darker than the one we saw through the viewfinder. This happens because the aperture gets adjusted later.
The common practice to overcome this issue it to press the ‘DoF’ button near the lens, while keeping the shooting button half-pressed. On doing this, the camera adjusts the aperture to the value set in the camera and the one that will be used for the photograph.
Now, my most logical question is this. Why is it not possible to change the aperture as per the setting in the camera? By doing so, the photographer will be able to see light the way it is going to appear in the final photograph.
If the aperture can be adjusted later for the shot, why not adjust it while composing the shot? By active adjustment, the photographer can see the amount of light coming through the lens and get a more accurate estimation of the final image. Having written about it, I am calling this method ‘Active DoF’, in contrast to the present method, which can be termed as ‘delayed or deferred DoF’.
If such a method gets implemented in cameras of the future, you know where it came from 😉
PS: I know that such behaviour is not possible for shutter speed.
PS2: Please note the use of an oxymoron – ‘accurate estimation’ 🙂