Speed Does Matter

What is speed? not what Ecstasy is cut with, No... Speed which refers to Cameras, or lenses to be specific. The speed of a lens refers to the highest aperture or lowest f-stop number which your lens can achieve, the lower the f-stop #, the faster the lens. So fixed 50mm f/1.2 (one of the fastest affordable lenses on the market today) would be faster than a Fixed 50mm f/1.4 or f/1.8..

Why is this referred to as speed...? Well lets start off by defining Aperture. without getting too technical and talking about the collumnation of light rays...

Aperture also refereed to as "f-stop" is referring to the diaphragm inside your lens which controls the amount of light that your lens will let in. The lower the Aperture, the less light that will be admitted through your lens and onto your CCD OR CMOS sensor where magical, and very technical things happen and your digital image is created. a Higher aperture, say f/1.4 will allow much more light through your lens, by opening up the diaphragm mechanism inside your lens.  here are some pictures i took to show this diaphragm on a 50mm f/1.4 Nikkor film lens (since aperture can only be adjusted through the camera on digital lenses).

F/1.4 

F/5.6

F/11

As you can see at f/11 only a tiny hole is open allowing much less light in, that at f/1.4


So... the Advantages of A faster lens - or lower f-stop - would be.... Since more light is let in at higher apertures, faster shutter speeds can be used. This is especially important in low light situations where you are trying to capture motion or have greater Depth of field - which I will cover in another post.  Say your indoors at night with only lamps and other lighting fixtures to light the rooms, and your shooting with a 18-200 f/3.5. Chances are that you will be shooting with a relatively slow shutter speed of 1/30th or 1/60th max, this will not be enough to capture motion other than a slight turning of a head or so. then say you all of a sudden get a 17-70mm f/2.8 lens. Under those same lighting conditions you would most likely be able to shoot at 1/120th to 1/200th of a second which will indeed freeze motion.
 Here's a simple example to kinda show this.. could be better but gets the job done...

 50mm focal length 1/80th sec and f/5.6

 Now.. 1/800th sec at f/1.4  what a huge difference in shutter speeds and although not perfectly focused (my bad) there is no motion blur

Allowing More light in and being able to use faster shutter speeds in lower lighting is only one of the benefits of fast lenses Depth of field is another which I will Write about in one of my next posts.

thanks to all who read hope this taught you a thing or two...