Question from 'Understanding Exposure' by Peterson

[smackitsakic]

Hi folks!

This weekend I picked up the book 'Understanding Exposure' by Donald Peterson at the suggestion of some of the posters on here.

So far, GREAT book!

As I was reading it last night I was on the section about storytelling apertures. I think it's around page 35. It speaks to using an exposure where everything is sharply in focus by pre-setting your depth of field.

I read this about 5 times and can't seem to grasp the concept of what Peterson is trying to tell the readers. Can anybody please try to explain to me what Peterson is trying to explain to me? How is it possible to pre-set the depth of field to get sharply focused images?

Also, my camera is a Canon and has a depth of field preview button...how does this relate to pre-selecting a depth of field?

Any help to this new photographer would be great!

Thanks.

 

[Goontz]

I don't have the book handy, but it sounds to me like he's probably just talking about using a certain aperture to get the depth of field that you want for your shot, then adjusting the shutter speed accordingly for the correct exposure (or maybe just using Aperture Priority mode).

Remember: Aperture size will directly affect your depth of field. Thus, choosing the appropriate aperture would be pre-setting your [desired] depth of field. This would be opposed to if, for example, you were shooting sports and you knew that a fast shutter speed is most important to freeze the action, and didn't care as much about your aperture or depth of field.

If you want a shallow depth of field for what you're trying to achieve, you'd use a large aperture (think f/1.8 - maybe f/3.5 or f/5.6 in the case of your kit lens). If you're shooting a landscape (which sounds like the case for a "storytelling" aperture) with everything in focus, you'd choose something more like f/13 or smaller. He'll refer to f/8-f/10 as the "I don't care" apertures because they're a middle ground for when a specific depth of field isn't desired. With these, the DOF wouldn't be as nearly as shallow as when wide-open, but would also not be as deep as with an even smaller aperture.

As for the DOF Preview button: Your camera has the aperture as large as it will go anytime you're simply looking through the viewfinder. This is so that it can let as much light in as possible so you can see through it. Right before it actually takes the exposure, it stops the lens down to whatever aperture you'll actually be shooting at. Pressing the DOF Preview button simply makes it stop the lens down to whatever aperture you're set at so that you can get an idea of how deep your DOF will be. Set your aperture to something small (f/10 or smaller). Look through the viewfinder at something and push this button. You'll notice that even things in the background will be more in-focus than they were before. It will also appear darker because the aperture is now stopped-down and not letting as much light through for you to see.

 

[Dominantly]

I believe it is Bryan Peterson that you are referring to.

Story telling apertures are basically shot at f/22, with the focal point set about 5ft from your lens (18mm is a good place to start with your focal length).

The idea of the "Story" is to have something interesting throughout the whole picture. For example, a nice set of rolling hills with flowers or tall green grass, then a nice old oak tree standing along in this field as your middle ground, then maybe a nice snow capped mountain range in the background.

 

[smackitsakic]

Thanks for the comments.

DOMINANTLY, what do you mean by having the focal point 5 feet in front of your lens? That is the part that I don't get.

In one of Peterson's examples he talks about setting the focal point to be 2 feet in front of the lens, set the depth of field, then move the camera to take the picture. This is the part that confused me, and still kind of is confusing to me.

I have a fairly good understanding of DOF and that a higher f-stop will result in a shallower DOF. It seems like Peterson is trying to tell readers that there is something more to it than this, but maybe i'm just reading it wrong.

I'll try to play around with the DOF Preview button on my Rebel. He mentions on a side note something about Canon cameras beeping if the DOF isn't appropriate, or something like that. It's written in a confusing way in my opinion. Am still a bit confused!

 

[Goontz]

Focal point is basically just the main point of interest in the shot; the object that you're focusing on. With a large aperture, it may be the only thing in focus, while with a very small aperture, everything would be in focus.

 

[Vinny]

I've never read the book but by pre selecting an aperture and pre focusing the lens you are taking shots with all the same depth of field/focus. The aperture is the mechanism that gives you the depth of field. A f 1.4 has a much narrower DOF than a f 11 than a f 22. Some people prefer aperture priority so they can control the DOF.

Personally I always had a hard time seeing the DOF in my camera (maybe that's something I need to work on!) but with digital it should be a simple matter of pointing and clicking.

As far as a camera knowing what depth of field is correct ... how does it know what effect you're looking for? I would ignore that section or turn that off in the camera.

 

[Goontz]

I've never read the book but by pre selecting an aperture and pre focusing the lens you are taking shots with all the same depth of field/focus. The aperture is the mechanism that gives you the depth of field. A f 1.4 has a much narrower DOF than a f 11 than a f 22. Some people prefer aperture priority so they can control the DOF.

Personally I always had a hard time seeing the DOF in my camera (maybe that's something I need to work on!) but with digital it should be a simple matter of pointing and clicking.

As far as a camera knowing what depth of field is correct ... how does it know what effect you're looking for? I would ignore that section or turn that off in the camera.

:scratch:

 

[Vinny]

What don't you understand Goontz?

I was explainig why you might set aperture and pre focus - did I explain something wrong?

The fact that I could never see depth of field through my camera is something I never worked on. I usually knew what look I was going for and took the picture with different apertures around what I wanted.

Camera not agreeing to the depth of field - you are in control of your photos.

Please explain.

 

[Dominantly]

Thanks for the comments.

DOMINANTLY, what do you mean by having the focal point 5 feet in front of your lens? That is the part that I don't get.

In one of Peterson's examples he talks about setting the focal point to be 2 feet in front of the lens, set the depth of field, then move the camera to take the picture. This is the part that confused me, and still kind of is confusing to me.

I have a fairly good understanding of DOF and that a higher f-stop will result in a shallower DOF. It seems like Peterson is trying to tell readers that there is something more to it than this, but maybe i'm just reading it wrong.

I'll try to play around with the DOF Preview button on my Rebel. He mentions on a side note something about Canon cameras beeping if the DOF isn't appropriate, or something like that. It's written in a confusing way in my opinion. Am still a bit confused!

What that means is you can point your camera to something 5ft in front of you, lock focus on it, then recompose and shoot.
I do not like to lock and recompose, so I would just move a focal point using the thumb pad, down to that point 5ft in front of me and do it that way.
This is suppose to ensure you have clarity throughout the whole scene, vice focusing on something further away and having a soft foreground.

 

[pbelarge]

I, like the OP am confused about how all this focusing and refocusing actually works. I think this thread has some good info and a couple of intelligent people here.

Could one or both of you try to explain it to us a little differently, maybe more detail? or maybe send a link that has this information available in a format that I (very inexperienced) can understand.

Thanks in advance of your response!!!

 

[smackitsakic]

This is the part that still confuses me:

What that means is you can point your camera to something 5ft in front of you, lock focus on it, then recompose and shoot.

I now understand what it means to have a focal point, but how do you lock focus on it? And what do you mean by recompose? That's the part that i'm not comprehending

Thanks for the patience with us newbies! Glad there are some photographers willing to share their vast knowledge!

 

[Dominantly]

So imagine that your camera has a cone shaped field of view attached to the lens cap (and it's rigid). If you aim the camera higher, the bottom of that cone points to a ground point further away. If you point it at a sharper angle down towards the ground, you gain more detail area closer to you, but loose some way off in the distance.
The bottom of that "cone" area where it is seeing the ground in front of you is your Hyper Focal Distance.
What does this mean? Well, the sharp portion of your photograph at an aperture of f/22 and a hyperfocal distance of 10ft, would be 5' to infinity. The closet point of clarity/sharpness is 1/2 of your focal distance. So if you were going for that lanscape shot, but focused on a set of trees 150ft in front of you, you would have robbed yourself of the maximum clarity and sharpness in the first large portion of your photograph.

Here is another example.

You have a Nikon D60, with the 18-55mm lens, your subject is 10,000ft away from you, and you want everything in the frame as sharp as possible.
Your Hyperfocal distance would be 2.41ft, AND your depth of field would extend from 1.205ft to infinity (1/2 of your Hyperfocal distance).


Check this website out
Online Depth of Field Calculator

 

[Dominantly]

This is the part that still confuses me:

What that means is you can point your camera to something 5ft in front of you, lock focus on it, then recompose and shoot.

I now understand what it means to have a focal point, but how do you lock focus on it? And what do you mean by recompose? That's the part that i'm not comprehending

Thanks for the patience with us newbies! Glad there are some photographers willing to share their vast knowledge!

So lock and recompose goes like this.

You have your center focus point, you point it at someones face, press the shutter halfway down to focus on them, then WITHOUT letting pressure off the shutter, you move the camera to frame your subject differently (IE move it so they are on the right of the frame vice the center). Then you press the shutter the rest of the way down.
What I do is I frame the photo how I want it, then I used the thumb pad to move the focal point to the subject, then I shoot.

Now imagine this, you are shooting with a 50mm at f/1.4 which has a very narrow depth of field, .03 feet in this case, you would have little room for error (IE if you were shooting at something 1' away, your acceptable sharpness would be 1.99' to 2.01'). Now Imagine you have a piece of string attached to the front of your lens and you have it stretched out to your subject 1ft away (lets say a coke bottle). Now if you set your focal point on the label and the string is the perfect length away from the label at that point, could you foresee the string distances changing if you were to move the camera and that lens position to recompose your shot? If you moved your camera 3" to the right to put the coke bottle on the left side of your screen, you would create a tiny bit more distance between it and the bottle. Now with .03ft to work with, can you see how you may have just caused your image to come out soft?

Hope my rambling makes sense.

 

[Goontz]

Dominantly said it pretty good. Locking focus and recomposing is really only a factor if you're using only 1 (and really only the center) focus point in your camera. If you're using an AF mode in which the camera selects 1 or more of its focus points to its liking, it's irrelevant to focus and recompose.

Like Dominantly said he does, some people will just select their own focus point based on where they want the focal point and not need to focus and recompose. Others will only use the center point, put the main subject in that focus point, then move the camera to get the composition that they want (maybe to follow the rule of thirds or get the subject off-center), while still holding the shutter release button down half way so as not to re-focus. This is a preference thing. Also stated above, in the case that you're using a very large aperture (f/1.4 to stick with the same example), the DOF is VERY thin so when you recompose you can potentially change the distance between the subject and lens, which could make the subject that you focused on become out of focus. Again, (because at 50mm f/1.4, the DOF is only .03' deep) moving your camera to recompose, the coke bottle is no longer within that .03' field that would leave it still in sharp focus.

 

[Goontz]

What don't you understand Goontz?

I was explainig why you might set aperture and pre focus - did I explain something wrong?

The fact that I could never see depth of field through my camera is something I never worked on. I usually knew what look I was going for and took the picture with different apertures around what I wanted.

Camera not agreeing to the depth of field - you are in control of your photos.

Please explain.

Sorry, I guess it was just sort of confusing to me. I was tired. I should have either explained better or not responded

"Pre-selecting" the depth of field, in the context of this book, is really just explaining not only the role of the aperture in DOF, but also how the photographer decides to use a certain aperture over another for any given shot. That is, it's not saying you should choose one aperture setting and one focal distance and shoot away. More like, if you know you want a shallow DOF, you will select a large aperture. If you want a very deep DOF, you'll select a small one. If it doesn't matter a whole lot, or you want something in between, you'd probably go f/8-f/10. The book is basic-level and laying down the fundamentals and thought process. Similarly, another part in the book explains that if you're shooting a moving subject, you will want to make sure your main priority is a fast enough shutter speed to freeze the action; you're not as concerned with what aperture is used.

As far as seeing DOF through the camera, remember that the lens is left wide open until right before the exposure is taken. Now, you won't really see just how shallow the depth of field really is through the viewfinder when it's wide open. But if you're selecting f/13 or f/22, you also won't see everything as deep/clear as the DOF would be in the actual shot (because the aperture is left wide-open until the shot is taken). This is where the DOF Preview button can come in handy.

The camera never knows what DOF is correct and it's not a section to be ignored or a setting to turn off. It's purely mechanical. All the button does is stop the aperture down without taking an actual shot, so you can view what the DOF will look like without having to take a shot.

I think I saw somewhere you shoot with a D90 (which is the lowest Nikon model to have a DOF Preview button, I believe). The button that's on the bottom right of the lens (as if holding camera normally and looking through viewfinder), probably in perfect reach of your right ring or middle finger, is your DOF Preview button. Set your aperture small, focus on something nearby, and look through the viewfinder. Now play with that button. There's no difference if you have aperture set wide open (because it's already left wide open), but it can be pretty useful when you start stopping down to get an idea what the end result will look like without having to snap a bunch of shots, look through them, etc. :thumbup: Hope that all helps.