posted by flosse_r on Explained!

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Well on a mechanical side, Aperture is a series of interlocking blades that form a circular opening and can be contracted and expanded as one. The best example is your eye (iris). In low light it becomes a big opening and in the sunlight it becomes a small(er) black opening, just like a lens in low light and bright light.:)

In order to improve  bokeh (background blur in a lens), manufacturers have changed and improved on the Aperture mechanism over the years from a 7 straight blade to a 9 striaght blade to 7 rounded and 9 rounded and even, rarely, up to 15 blades. With the amount of blades and rounding or straightness the circle and out of focus blur changes.

Examples of Aperture blades: 7 straight, 7 rounded, 9 straight and 9 rounded

Now you might wonder where The numbers associated with Aperture come from. Well, the Aperture number is actually just a ratio. It is very simply the focal length divided by the diameter of the aperture opening. For example a 50mm f2 will have an opening (diameter) of 25mm or reversed, a 50mm lens with an aperture opening of 25mm is f2. A 50mm lens at f1.4 will have an aperture opening of about 36mm. So you see it actually comes all down to mechanical things

The difficult part comes when we talk about f-stops or full stops, 1/3rd of a stop or 2/3rds of a stop.

Ok, so the actual definition of a full stop is basically every time the light halves or doubles is a full stop. There is a neat line which might not make sense but these are the full stops from f 1.4 to f22

1.4 -> 2.0 -> 2.8 -> 4 -> 5.6 -> 8 ->11 ->16 -> 22

So from f 1.4 to f2.0 the light that is being let through halves, that is one stop. Yes you have many lenses with numbers in between the full stops but as long as you are aware that these are the full stop numbers and anything else is in between you have a pretty good idea of what is going on. To know exactly what is calculated and how for the stops in between, see this site.

As you can see, the faster lens the better in terms of shutter speed and aperture ratio (explained  HERE) BUT, the longer a lens and faster, the bigger it will be. For example, my 80-200mm F2.8 nikon means that it has an front element of 72mm, that makes the lens big and heavy, especially since it needs to maintain the 2.8 all across the zoom range. But then you have crazy lenses like the 600mm f4 which has a front element of 150mm or 15cm!! So these lenses become large and crazy to carry around but they get you an amazing focal length with a very fast (for the length) Aperture to take pictures at a large distance.

So, now that you know a little bit more about Aperture, go get lenses that are fast There are plenty of cheap lenses around but they are mostly primes and they will not break the bank.

Tags: aperture, blades, f-stop, fstop, lens, lenses, light, opening, stop