Aperture, Shutter Speed, Exposure, DoF

[kjmdrumz3]

This is intended for the novices among us.

I have been poking my head around the internet lately reading different explainations on aperture and shutter speed and how they relate to exposure and depth of field. It seems the "how do I control the blurriness of the background" question comes up from time to time. Most of what I read was accurate, but some of it was just plain confusing (through a novices eyes, anyway.) This is not intended to be scientific, just a down and dirty with some images as examples. I'm going to leave ISO out of it.

Aperture controls the amount of light entering the camera by the size of the opening in the lens. Shutter speed determines the amount of light entering the camera by how quickly (or slowly) the shutter releases. These two are DIRECTLY related.

Aperture + shutter speed= Exposure and DoF (depth of field, or how blurry the foreground and background of the image is.)
That being said, you may have also heard the terms stop(s) or f-stop(s). Stop(s) can refer to either the aperture or shutter speed setting, whereas f-stop(s) refers to only the aperature setting.

1 stop is doubling (or halving) the amount of light entering the camera. 2 stops would be doubling (or halving) once more and so on.

When talking shutter speed, it is exactly that. If you double your shutter speed, you have 1 more stop of light. It works the exact opposite when halving shutter speed.

In relation to aperture, it is a little trickier. Doubling or halving the aperture number is actually 2 stops of light. You may see where this could get a little confusing. But, alas, there is an easy way to get exactly 1 stop. Many DSLR's let you control aperture by 1/3 of a stop at a time. Meaning moving either direction 3 settings will either be 1 stop or -1 stop of light. Check your camera's manual- if it let's you adjust by, say, 1/4 of a stop just move in either direction 4 times and you will have your 1 stop or -1 stop.

Remember me mentioning that aperture and shutter speed are DIRECTLY related? Here's how. We will use my first 2 images as an example:

Image 1 was shot at f/1.4 @ 1/10th of a second. To get the same exposure, Image 3 was shot at f/2.8 (two stops less light) @ 1/2.5 of a second (halved and halved again to compensate for the 2 stops of light lost by adjusting the aperture. Just remember to use the same ISO setting in your camera for both images.) The longer shutter speed compensates for the smaller (larger number) aperture and allows the right amount of light in for the same exposure.

Did you notice anything different about the two images? Of course you did. The socks and box of image 1 are more blurry than those of image 3. This is Depth of Field at work. Here is the simple explaination: The larger the aperture (smaller f-number) the shallower the depth of field (the more the foreground and background are out of focus). The smaller the aperture (larger f-number) the deeper the depth of field (the more in focus foreground and background look). Bottom line- Aperture controls Exposure and Depth of Field. Shutter Speed controls Exposure only.

Again, this was a fairly simple (as simple as I could make it, anyway) explaination of how these all relate to each other. Below I have 8 pictures in a series. In addition to reading the relationship, I wanted to show you the relationship. I know I learn better from seeing. Feel free to try something similar yourself. It would only help you to remember what was just discussed!

Camera settings: ISO 400. Distance from socks was 36-inches, from giraffe was 100 inches, and from box was 160 inches.


Image 1- f/1.4 @ 1/10th of a second:
http://farm3.static.flickr.com/2440/3677033759_af6ddc81ff.jpg

Image 2- f/2 @ 1/5th of a second:
http://farm3.static.flickr.com/2662/3677033941_03e305d9a5.jpg

Image 3- f/2.8 @ 1/2.5th of a second:
http://farm3.static.flickr.com/2467/3677034131_eaf08de490.jpg

Image 4- f/4 @ 1/1.3 of a second:
http://farm4.static.flickr.com/3644/3677034301_cdd162546a.jpg

Image 5- f/5.6 @ 1.6 seconds:
http://farm3.static.flickr.com/2475/3677034469_381dda8c41.jpg

Image 6- f/8 @ 3 seconds:
http://farm4.static.flickr.com/3650/3677850168_f1474d4661.jpg

Image 7- f/11 @ 6 seconds:
http://farm3.static.flickr.com/2631/3677034809_8cf9f26e8a.jpg

Image 8- f/16 @ 13 seconds:
http://farm4.static.flickr.com/3590/3677034979_b028c59060.jpg

[cdifoto]

Bottom line- Aperture controls Exposure and Depth of Field. Shutter Speed controls Exposure only.
Shutter speed also controls the blurriness or sharpness of moving objects. Fast shutter speed = frozen football player. Slow shutter speed = blurred football player. It also depends whether you'll get a shaky photo or a crisp photo. Slow the shutter down too much and you won't be able to stay still enough. Speed it up and your coffee induced vibrations aren't visible in the image. If you're using flash it gets even more complex (kinda). Too fast and you get a black bar unless you use High Speed Sync (if available) because the camera can only sync at or below certain shutter speeds. Use High Speed Sync and you cut down the range of your flash.

[kjmdrumz3]

Shutter speed also controls the blurriness or sharpness of moving objects. Fast shutter speed = frozen football player. Slow shutter speed = blurred football player. It also depends whether you'll get a shaky photo or a crisp photo. Slow the shutter down too much and you won't be able to stay still enough. Speed it up and your coffee induced vibrations aren't visible in the image. If you're using flash it gets even more complex (kinda). Too fast and you get a black bar unless you use High Speed Sync (if available) because the camera can only sync at or below certain shutter speeds. Use High Speed Sync and you cut down the range of your flash.

You are exactly right but I'm trying to stick with the very basics here. What you posted is another animal completely!

[cdifoto]

There's no point in posting just the basics because someone will read it, think it's that simple, then get frustrated and confused because it's not.

[FLiPMaRC]

There's no point in posting just the basics because someone will read it, think it's that simple, then get frustrated and confused because it's not.

I agree. And leaving out ISO doesn't help either. How do you explain exposure without ISO?

[kjmdrumz3]

This was supposed to answer the question of how to control depth of field.

[TheWengler]

This was supposed to answer the question of how to control depth of field.

I think you're leaving out some important things. It's possible to keep it simple, but still give people all the pieces.

[cdifoto]

It's not simple to most newbies but if you're gonna dumb it down you may as well just tell them to stick with Program or full Auto. If you only tell them how to adjust the aperture and why, but don't tell them about the other caveats, you do them a disservice and potentially make things worse. "I closed my aperture down to get my entire group in focus but now my pics are all dark or blurry!" "Wait what? I need to adjust my ISO and make sure my shutter speed isn't too slow? You didn't tell me that before! What's ISO anyway?"

IMHO.

[kjmdrumz3]

Well, post the missing info and we will incorporate it into the original post. I didn't claim to know everything, or explain everything. Just trying to give a basic understanding of how it all works together. I want this thread to be beneficial to any novice reading, so write it out and we'll do it!

[cdifoto]

I'm not gonna type that all out when it's already available in a whole myriad of books and tutorials. Beyond the basics, you can't possibly include everything there is to know about photography in a thread post anyway.

[Mark_48]

Maybe if the thread title had been "Depth of Field-What It Is and How to Control It". I wasn't quite sure of what the core subject was about as I started to read through.

As the comments are indicating, your lesson in DOF sort of needed a prerequisite lesson titled, "Exposure -The 3 Things in Life I Need to Know". :)

And then as a preface to your explanation of DOF....
"Presuming the reader has an understanding of the fundamental concepts of exposure and how aperature, shutter speed, and ISO determine said exposure, this is will be a brief discussion of how those elements affect and control depth of field, otherwise simply known as DOF."

It's sometimes not easy to put collective thoughts to words. You did well in your effort and I can only commend you for it, particularly with the intention of helping others with similiar interests. I have no doubt that in composing this you've become an "expert" on the subject of DOF.

Is bokeh the same thing as DOF? :D

[cdifoto]

Bokeh is a jokeh.

[kjmdrumz3]

Maybe if the thread title had been "Depth of Field-What It Is and How to Control It". I wasn't quite sure of what the core subject was about as I started to read through.

As the comments are indicating, your lesson in DOF sort of needed a prerequisite lesson titled, "Exposure -The 3 Things in Life I Need to Know". :)

And then as a preface to your explanation of DOF....
"Presuming the reader has an understanding of the fundamental concepts of exposure and how aperature, shutter speed, and ISO determine said exposure, this is will be a brief discussion of how those elements affect and control depth of field, otherwise simply known as DOF."

It's sometimes not easy to put collective thoughts to words. You did well in your effort and I can only commend you for it, particularly with the intention of helping others with similiar interests. I have no doubt that in composing this you've become an "expert" on the subject of DOF.

Is bokeh the same thing as DOF? :D

Thank you for this post! This is exactly the type of contributory information I was looking for. Not "you left this out or you left that out, but I don't feel like typing it out". My goal here is not to bicker, but to help someone who is just getting into this understand it. We all know that at first it seems overwhelming. I will update my original post sometime this evening. Again, +1 to you for contributing!

[amistill]

Thanks!! kjmdrumz3

Your post was extremely useful. I've been taking photgraphs a while, but this is a neat little explanation.

Other experienced members may have a point, and so does Mark, as to what the title implies.

But it's a great post. Learning 'complex' subjects must be done by learning each individual 'concept' at a time, and often requires us to deliberately exclude the 'neighbouring concept' so that one idea becomes clear, until we move to the next.

Now I know why I would want to use a larger aperture + Faster Shutterspeed = > DoF

Neat!

[Karisu]

Regarding depth of field, I noticed some aperture priority cameras are limited in how wide they can open up their apertures. If I were looking to take shallow depth of field portraits, what F-stop minimum (maximum?) should I be looking for?

Are wide angle lenses or super-zoom lenses more suitable for depth of field control?

[TheWengler]

Regarding depth of field, I noticed some aperture priority cameras are limited in how wide they can open up their apertures. If I were looking to take shallow depth of field portraits, what F-stop minimum (maximum?) should I be looking for?

Are wide angle lenses or super-zoom lenses more suitable for depth of field control?

There's are no set numbers. You do need a DSLR though. This tool will help give you an idea...

http://www.tamroneurope.com/dof.htm

[AlexMonro]

Regarding depth of field, I noticed some aperture priority cameras are limited in how wide they can open up their apertures. If I were looking to take shallow depth of field portraits, what F-stop minimum (maximum?) should I be looking for?

Are wide angle lenses or super-zoom lenses more suitable for depth of field control?

To get shallow Depth of Field, you need a combination of the following factors:

Wide Aperture (low f number)

Long Focal Length (actual focal length, not "35mm equivalent")

Short distance to subject.

In practice, this means that it's easier to get shallow depth of field effects with the larger sensor of a DSLR, preferable full frame, than it is with the tiny sensor of most compacts.

For shallow DoF portraits, most people seem to find the best results are achieved with a DSLR and a lens of 50-100mm focal length and an aperture of f/1.4-f2. Full frame sensors might use slightly longer focal lengths for full face close up portraits, say 70-150mm.

For a detailed article on Depth of Field, with an on-line calculator you can try plugging some numbers into, click here (http://www.cambridgeincolour.com/tutorials/depth-of-field.htm).

[Karisu]

Thanks! The article and calculator were very helpful.