Aperture And What It Does.

Nikon_Guy · Jun 6, 2007

Most likely, the most important thing for a new photographer to learn and understand is aperture and how it can change the look of a finished picture. The aperture is simply a series of blades within the lens that are able to constrict or expand in the pattern of a circle. This action controls the amount of light that is able to reach the film or image sensor within the camera and controls image sharpness and depth of field as well as minor corrections to lens aberrations. This function is similar to the iris in your eye. Think about what happens when you walk from a very dark room into one that is extremely bright. Your iris will go from a very large opening to one that is very small to limit the amount of light entering the eye. This same action when done with your camera lens is referred to as â€œstopping downâ€.

Because aperture settings are listed in fractions they are referred to as â€œf-stopsâ€. Each f-stop controls the light in a ratio of 2 to 1. Here is where it can get confusing to some people. The larger the f-stop number is, the smaller the diameter of the aperture opening will be. . For example, if you change the f-stop from 5.6 to 8 you have limited the amount of light reaching the image sensor (or film for us old guys) by half.

Hence, when you hear someone refer to â€œstopping downâ€, they are actually using a higher f-stop number which lessens the amount of light. Confused yet? I know I was.

As I continue this missive, I will explain how aperture affects depth of field, what depth of field is as well as image sharpness.

Chelsey · Jun 6, 2007

This thread is much appreciated

I am terrible when it comes to understanding aperture...I get majorly confused

surfn · Jun 6, 2007

can't wait to hear the explanation on depth of field and sharpness......

slightly off topic, but how you can test your camera (not the lens) to make sure the mirrors and sensors are alligned and functioning normally? (i only have one camera......do camera shops work on them? or do you have to send it to cannon for a tune up?)

rocko918 · Jun 6, 2007

awesome. thanks for the help and look forward to more!

Zoanuts · Jun 6, 2007

Great help to those who don't quite understard the are of taking pics. Including me!! Keep it coming

Nikon_Guy · Jun 6, 2007

I have learned long ago that when trying to fix or adjust the inner workings of a camera myself, I normally screw it up worse than it was.

I have a fantastic shop that does all my repairs, adjustments and cleaning for me. I'm sure if you look in the Yellow Pages under Camera Repair you will find factory auth repair places near you.

surfn said:
can't wait to hear the explanation on depth of field and sharpness......

slightly off topic, but how you can test your camera (not the lens) to make sure the mirrors and sensors are alligned and functioning normally? (i only have one camera......do camera shops work on them? or do you have to send it to cannon for a tune up?)

Nikon_Guy · Jun 6, 2007

Aperture and depth of field.

When you point your camera at an object and either manually focus or auto focus on that subject, everything that is on the same plane with that subject will be in sharp focus. As portions of the scene you are taking a picture of get farther away from the focus plane (the object you are focusing on) they will become less sharp. Fortunately, the human eye cannot perceive tiny differences and even though objects will start to loose their sharpness as soon as they leave the focus plane, the amount isnâ€™t immediately discernable to the human eye. The area in front of and behind the focus plane that appear sharp to the human eye is referred to as acceptable range of sharpness or the depth of field. A more detailed method of describing and showing what happens with depth of field and acceptable range of sharpness is referred to as the â€œCircle Of Confusionâ€ but at the risk of making this more confusing than it already is, I will not go into it at this time.

For our purposes the most important thing to keep in mind is that the smaller the aperture opening is, the greater the depth of field will be. Keep in mind that as the f-stop numbers on the lens or in some cases inside the camera get larger the smaller the aperture opening will be. For example f-8 is a smaller opening than f-4. Knowing this to be true, a person might be tempted to use the highest numbered f-stop (the smallest aperture) the camera has to offer to obtain the greatest depth of field. Unfortunately, this can and does backfire on you because at the smallest aperture opening the ratio of diffracted to non diffracted light becomes such that the overall image will suffer in quality, negating the increased depth of field. Most lenses do perform better at smaller aperture settings but when reaching a certain point the scales tip in the other direction because of light diffraction.

For most purposes I suggest most images be taken somewhere between f-5.6 and f-16. It is my experience that most lenses perform best somewhere between f-8 and f-11. If you are not getting a suitable depth of field at those settings, remember the farther the front of the lens is from the focal plane the greater the depth of field will be. For instance, if you are doing a shot of a group of people standing three deep and just cant get the folks in front and behind in focus try taking a few steps backward to increase the depth of field of that shot. The same can be done when taking pictures of items in your reef.

Next up I will explain how to broaden the depth of field in your pictures by finding the hyperfocal distance.

JGoslee · Jun 6, 2007

Awesome thread! Thanks Nikon Guy.

zoanthidman · Jun 6, 2007

http://www.ximinasphotography.com/lessons/

fishes2889 · Jun 6, 2007

Hey Jeremy- What camera do you have?

fishes2889 · Jun 6, 2007

Very nice pics BTW and great prices on it. (amazon.com)

Nikon_Guy · Jun 6, 2007

coralnutz said:
Great thread. Thanks for taking the time to help us out.

I've been trying to read up on stuff and been surfing around the POTN site a lot trying to learn some stuff. When someone refers to a greater depth of feild I'm not sure if they mean more of it is in focus or the subject is more in focus? Not sure if that make sense, but here's a photo as an example. Which one would have the greater depth of field? (sorry the pics aren't that great)

The top one was f8.0 and the bottom one was f3.5 (both had a focal length of 6.0 mm if that means anything)

As you can see the top one, more is in focus, but overall I think the polyp I was actually shooting for wasn't quite as in focus as the bottom one where the background is more blurry and in a shorter distance.

What an excellent example of how to use depth of field properly to create a desired look and feel to a picture.

Although the depth of field is greater on the first picture, (more of the picture falls into the acceptable range of sharpness) the second picture accomplishes what you set out to do as well as makes a much more pleasing picture to look at.

In the second picture the eyes are drawn to the purple play in the foreground as it is in sharp focus and the less sharp red palys in the background make a nice contrasting color to really set off the primary subject of the picture (the purple paly). After the viewer has a good look at the purple paly in the foreground they then let the eyes wander to the less sharp areas in the background. This is an instance where less is more if you will.

Indeed, when “more depth of field” is used as a term in normally means a greater distance from front to back that will be in the acceptable range of sharpness. Remember, depth of field or acceptable range of sharpness doesn’t end abruptly, it is gradual.