What the F? Understanding what the F means in photography.

February 19, 2015  •  Leave a Comment

What the F?  Just exactly what that f letter means in photography.

Have you ever looked at your camera lens and seen the letter "f" and seen a number with it and wondered exactly what that means? 

Wonder no more intrepid reader!!! (Oh, to our pro-photographer friends...You might want to head on over to Amazon and do a new "Camera Gear" search...This is geared more for our advocational photography friends out there!)  

We are going to tell you all the "F" you ever wanted to know.Way back when, it stood for "Focal Ratio".  Now it is expressed as a number that you will see on almost every camera lens (even point and shoots have them) to let you know just how much light the lens is capable of "seeing" in at it's maximum value.  

For example: 

It will help if you think of a camera lens as a large mechanical eyeball.  It works pretty much the same as one.  Think of the film (if you're old enough) or the sensor (if you're younger than 16 :) ) as the back part of your eyeball.  Think of the front part of your eyeball as the outside "lens" of the camera.  Inside the barrel (tube) of each lens is a contraption made of little "leaves" that open and close mechanically that are called an "aperture".  This works just like the pupil of your eye. 

Think of an undilated as a value of f22 (very tiny opening) and a dilated pupil as having a value of f2.8 (fairly large opening).  The f22 literally needs very little light to make an image.  It is used when there is a lot of light around  i.e. sunny days, very bright in doors lights.  The f2.8 literally needs a LOT of light to make an image, therefore the pupil or aperture is opened up very widely allowing the most light possible to come in.  

When you see a lens and it has f2.8 or f3.5 or f4 written on the front of the lens ring, that is a "code" to let you know how much the "maximum" amount of light can be let into that lens at its widest aperture.

If this isn't confusing enough to learn...The numbers are counter-intuitive or counter-indicative.  I.e. The higher a number is (f22) the less light it actually allows into the camera to the film/sensor.  The lower the number, the more light it allows in.  

When you hear photographers talk about "fast glass" that means a lens that allows the most light possible in at it's maximum (lowest f#) aperture.  Most professional photographers won't even bother with a lens that isn't capable of an f2.8 or lower because of a number of reasons.

Another note...The lower that number, the higher amount of $ you can expect to pay for the lens.  It takes quality and a lot of technology to get that number down...That means $$$ in the end for you the picture taker person.

Here's one of my favorite lenses in the world.  It is a 20mm f2.8 Nikkor (Nikon Optics Corporation) It's a pretty wide angle (allowing a LOT of image in a frame) and it's fairly "fast" (low f-stop).  

As you can see, the numbers towards the bottom of the image that are 22,16,11,8,5.6,4.2.8.  Those are all f-stops.  If you're good at math, you'll notice that going from one direction or another, that these numbers double or half each other in sequence.  That's because the f-stop ratio represents an effective doubling or halving of the amount of light each time the number is raised or lowered.

Those numbers can also help you do some other amazing things with your camera...That we'll talk about next Theoretical Thursday when we get "IN DEPTH with DEPTH OF FIELD". (Cue dramatic music!!!) 


To keep up with all the goings on with Ikon and our gang of rowdies, be sure to "Like" us on Facebook at http://www.facebook.com/ikonphotographs

Each Thursday we attempt to de-mystify something about the science of the art of photography and each Friday, we give away a free Ikon Photographs original art print with our quiz contest "FREE ART FRIDAY".  Don't miss it!!! 



No comments posted.