Lesson 1: Aperture Settings. a.k.a. f stops

Disclaimer: I know nothing, and I claim to know nothing.  The reason I’m doing things this way is because I believe that you don’t truly understand something, until you are able to teach it to someone else (It’s even better if you can teach a 4th grader something, that’s the real challenge).  Also, I might teach something that is totally wrong, and that’s okay we’re all learning.  Simply comment, correct me and I’ll appreciate the help.

 

Definitions (photographytips.com)

APERTURE - A circle-shaped opening in a lens (a hole, really) through which light passes to strike the film/sensor. The aperture is usually created by an iris diaphragm that is adjustable, enabling the aperture to be made wider or narrower, thereby letting in more or less light. The size of the aperture is expressed as an f-number, like f/8 or f/11.

f-NUMBER - (ƒ-number) A number that expresses a lens’ light-transmitting ability – i.e. the size of the lens opening. Usually found on the barrel of a lens, f-numbers indicate the size of the aperture in relation to the focal length of the lens. A smaller number indicates a larger lens diameter. ƒ/1.4 signifies that the focal length of the lens is 1.4 times as great as the diameter. All lenses set at the same f-number transmit the same amount of light.

ƒ-stop - (f-stop) A lens aperture setting calibrated to an f-number.

 

 

So, what I’ve learned so far about aperture is that it functions like the pupils in your eyeballs, expanding and contracting as needed depending on the amount of light in the room or place where you are.   Ok.  That makes sense.  When the doctor sticks a shiny flash light in my eye, my pupils get tiny.  So l just went to the bathroom (a dark room) and turned off the light for 30 seconds and then turned the lights back on…  Guess what?  I could see my pupils shrink real quick in the mirror.  I know this is a trick we did as a 4 year old, but it really helps me understand why aperture is important in photography.  My pupils in a dark room expand in an attempt to capture as much of the light that’s in the room.  And when I turn the lights back on, my eyes don’t need as much light to see, so my pupils shrink back down.  The same concept works with the diaphragm of the camera.

 

So what do the f numbers mean?  Where do they come from?  The f/numbers relate the diameter of the diaphragm to the focal length of the lens.  Let’s say that your lens has a focal length of 50mm.  Then an f/number that reads as f/2 would mean that your diameter (size of the hole passing light into your camera sensor) is 25mm.  So for all you algebra nerds (I’m on of them) :

Focal Length / Diaphragm Diameter = f number

 

If you also notice, f/numbers should be seen as fractions.  It would be easier to assume that the bigger f/number, the more light comes in, but that is not the case.  Just like 1/2 a pizza is more food goodness to intake in my belly than 1/4 of a pizza, the larger the f/number the less goodness (light) is brought to the sensor inside the camera.

 

So far I feel like I’m an idiot for breaking it down to pizza and my eyeballs, but at least I get it!  And now that I know the basics, I can build upon that.

 

While researching the f/numbers, I also figured out that the aperture affects the depth of field and not just the amount of light needed for a good exposure.  Depth of field is the amount of stuff around/behind/in front of your focus point that is in focus as well.  So, let’s say you are in a bowling alley and the entire cast of The Office is bowling 2 lanes away from you.  That would be the best picture for my blog – me bowling side by side with Jim!  Well if I want to take this picture without having to ask the celebrities for a posed shot, I have to make sure that I have the proper depth of field set up to capture both me and Jim 2 lanes down bowling.  I mean, if it’s all blurry in the background, who would believe me?  

 

Then again, less depth of field can be a very interesting composition tool.  For example, let’s say I’m at a Mets game with my wife and she just looks amazing in her Atlanta Braves shirt – I’ve got to get a picture of this!  But what’s the worst part about being a Braves fan at a Mets game???  Mets fans.  By setting the small depth of field, I can focus on her and ignore all the Mets fans in the background!

 

The way I learn is by doing, so with each lesson I’m going to be creating a fun photography exercise to put into play the concept that I just learned, and then I’ll do a quick debriefing afterwards.

 

***To eliminate as many factors as I can, I will be shooting in Aperture Mode (A) on a tripod, with no zoom, and no flash.  This way I know that the difference in each picture relates directly to what I’m adjusting.***

 

Items you’ll need :

* Camera (I’ll be using a Nikon D70s)

* 3 sheets of paper with the word FOCUS written or typed on the bottom half of the page.  As big as it’ll fit.

* A large room.

* Tripod (or the ability to stay still and take multiple pictures from the exact same spot…which I’m not blessed with!)

 

1)  Okay, once you’ve printed out the 3 FOCUS sheets of paper fold them in half.

 

2)  Now set them up around your room at these intervals.  1st one at about 4 feet in front of your camera, the second one at 8-10 feet, and the third one at 20-25 feet.  Make sure that all the sheets can have the word “FOCUS” read at the same time through the viewfinder of your camera.

 

3)  Now try to get only the first “FOCUS” in focus.  Note the f number.  (f/1.8)

 

4)  How about getting the first two in focus?  Note the change you are making? (You might need to peek down at your LCD screen to notice the difference. (f/8)

 

5)  Can you get all three in focus?  Note the f number. (f/22)

 

 6)  Now try some extra aperture settings.

 

See, that was fun right?  Study your results and you’ll see how your aperture settings affect Depth of Field.

 

Please feel free to post your pictures and results on this page.  I found the higher the aperture number (which means the smaller the diaphragm), the more I got in focus.  So:

higher f/number = more depth  

 

That’s easy.  The lower the aperture number (the larger the hole is for light to travel through), more isolated the main focal point was.  So:

 lower f/number = less depth

 

Thanks for your time, and go teach a 4th grader about aperture!

 

Chris.