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<blockquote data-quote="Horoscope Fish" data-source="post: 580755" data-attributes="member: 13090">Because the 18-55mm is a variable aperture lens. Look at the gold print on the lens barrel. You see where it says &quot;1:3.5-5.6&quot;, right? That's the aperture range of that lens: f/3.5 to f/5.6 and that lens can only open up to f/3.5 at its widest focal length of 18mm, or very close to that. As soon as you begin to zoom in, the maximum aperture it can achieve will get smaller until it reaches f/5.6 where it will stop decreasing based on focal length. This is common for zoom lenses; as focal length INcreases, maximum aperture DEcreases. At it's maximum focal length of 55mm that lens will have a maximum aperture of f/5.6 no matter what.Constant aperture glass does not do this but it's also more expensive typically speaking. For example my Tamron 70-200mm f/2.8 is constant aperture, it has a maximum aperture of f/2.8 across the entire focal length. But believe me... I paid dearly for that.</blockquote>

[QUOTE="Horoscope Fish, post: 580755, member: 13090"] Because the 18-55mm is a [I]variable aperture[/I] lens. Look at the gold print on the lens barrel. You see where it says "1:3.5-5.6", right? That's the aperture range of that lens: f/3.5 to f/5.6 and that lens can only open up to f/3.5 at its widest focal length of 18mm, or very close to that. As soon as you begin to zoom in, the maximum aperture it can achieve will get smaller until it reaches f/5.6 where it will stop decreasing based on focal length. This is common for zoom lenses; as focal length INcreases, maximum aperture DEcreases. At it's maximum focal length of 55mm that lens will have a maximum aperture of f/5.6 no matter what. Constant aperture glass does not do this but it's also more expensive typically speaking. For example my Tamron 70-200mm f/2.8 is constant aperture, it has a maximum aperture of f/2.8 across the entire focal length. But believe me... I paid dearly for that. [/QUOTE]

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