Blown highlights

Have you ever been annoyed with this in one of your pictures?

Blown highlights in the cloudy sky.

This is a common problem in digital photography where either the selected exposure or the camera sensor itself will push whole regions of the picture into complete white. This is why it is called blown highlights, as the highlights, i.e. the light parts of the picture, become totally white, hence "blown".

The question is, why does this happen and how can you prevent it?

Photography basics – ISO

The ISO rating was originally a measure of film sensitivity.
 
Films are rated for a certain ISO, this defines the sensitivity of the film to light. A film with a lower ISO number needs more light to make the same image than a film with a higher ISO number.
 
What does ISO mean in the digital world?
 

Photography basics – Shutter Speed

The shutter speed is the duration during which the shutter of the camera stays open to let light shine on the sensor or film.
 

Photography basics – Aperture

The aperture controls how much light is let in by the lens.
 
Lenses have variable aperture, making it possible to let in a lot of light for low light conditions or let in only a fraction of the light for those sunny days. This is one of the ways to adjust the exposure of a photograph, or in other words to control the amount of light that falls on the sensor or film.
 

How Many Megapixels Do You Need?

The answer to this question depends mostly on what you want to do with your pictures.
 
If you want to just view your pictures on your computer screen, you do not need many megapixels at all. The typical laptop sold today comes with a screen with around 1 megapixels. Most high end screens do not have more than 2 megapixels.
 

Crop Factor

The crop factor specifies the relative size of a sensor. The reference size is almost always taken as 35mm film, where each frame has a size of 36×24mm. This is also known as “full frame”. The crop factor then is the diagonal of this divided by the diagonal of the specific sensor in question. Since the smaller sensor “crops” the picture, this ratio is called the crop factor.
 
There are some interesting things that result from the use of a cropped sensor (a sensor smaller than full frame).
 

High ISO Noise = Grainy Photos

One of the situations where compact cameras really struggle is low light situations. The following are some examples of what happens when you shoot at high ISOs in (usually) in low light. You usually end up with grainy photos. (Click on the picture to see it larger.) That is noise caused by pushing a small sensor too far. The higher the ISO value, the less light the sensor has to work with. Have a look at the ISO article for a more detailed explanation.

Deciphering Lens Acronyms – Nikon Edition

 
 
New lenses all have bunch of acronyms attached to them.
 
Here is a simple guide to the more recent Nikon lenses to understand what these all mean, and to understand if any of this is important: