Question from 'Understanding Exposure' by Peterson

Vinny · Apr 7, 2010

Thanks for explaining!

I haven't read that book but have read "Joy of Photography" years ago and am reading "Fundimental of Photography" now to bone up on what I have forgotten over the years and see what's new in digital. Maybe in trying to explain aperture I stuck my nose in where it didn't belong!

Both my cameras have the DOF preview, but for me I never found it useful since I mentally think about what I want want and in film I would tweak the photos with bracketing. This is a technical area area that I probably should develop ... with digital it is quicker to see the results.

When smackitsakic posted about the camera beeping made me think that it may stop you from taking the photo, that's why I commented on it. I think the D90 will prevent you from taking photos in some modes if it doesn't think something is correct.

Boomn4x4 · Apr 7, 2010

smackitsakic said:
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.

I just read that page two nights ago... and know exactly what you are talking about.

Everyone is giving you correct information, but they havn't answered your specific question.

When the author says "by presetting your depth of field" he is speaking of your "depth of field preview button".

Typically, when you set your aperture for a depth of field, you are doing so blindly. The image you are seeing through your view finder is displayed as if you were shooting with a wide open aperture. If you were to adjust your aperture, the image you see in your viewfinder will not change. If you set your aperture at f/8 or f/22, it will look exactly the same to you so you really only have a "best guess" as to how the depth of field will be when actully exposed.

The depth of field preview button will close the aperture to your preset aperture, so that the image you see through the view finder looks exactly as it will be exposed. You set your aperture to f/8, and hit the depth of field preview button, and the camera will close the aperture to f/8 and you will see in your viewfinder what that will look like once you take the picture.

Dominantly · Apr 7, 2010

With a stroytelling aperture ( your smallest aperture), there is no real need to use the dof preview, as you are setting everything for max.

I use the dof preview in a flower field for
example, to see what aperture I find gives me the dof for the image I have in my head if how I want it to look, and it's usually around the f/8-f/11 range

smackitsakic · Apr 7, 2010

Sweet, I think this is making sense. I have done the 'focus and recompose' a few times without knowing that I was focusing and recomposing. Nice to know that it's that simple

I think I was reading into the book a little too much, trying to understand every word of it. But, that being said, it is really sweet coming on here with any questions I have to clarify.

Also, I took out my camera at lunch and played around with the DOF preview button. I had played around with it before, but I didn't have a high enough aperture (f4) to notice a difference.

Awesome!

While we're on the focal point topic...in manual mode on my canon rebel I only get the centre dot as the focal point. Am I able to move this with the shutter button pressed halfway down by adjusting the focal point with the arrows on my camera? Or is the focal point always the centre dot in manual mode, making you focus and recompose?

Thanks everyone in this thread!!

Goontz · Apr 7, 2010

smackitsakic said:
While we're on the focal point topic...in manual mode on my canon rebel I only get the centre dot as the focal point. Am I able to move this with the shutter button pressed halfway down by adjusting the focal point with the arrows on my camera? Or is the focal point always the centre dot in manual mode, making you focus and recompose?

Thanks everyone in this thread!!

That part of your question may be Canon-specific (I shoot Nikon). I'm sure a Canon user will chime in on that.

I know that on Nikon, if you have the AF mode to where you select which point it's using, you can move it around with the arrows on the back of the body. Even in Manual mode, I can use different AF modes (be it 3d, me selecting which single point, camera choosing whichever points to use, etc). Once you have the shutter button half-pressed, that "locks" the focus -- after half-pressed, you won't be able to change whichever focus point it has focused on.

As an example, lets say you have something in the bottom right 1/3rd that you want as the focal point. You should be able to use the arrows (push down once and right once maybe for example's sake) to select the focus point closest to that. Then you would use the shutter button to focus and shoot away.

smackitsakic · Apr 17, 2010

Dominantly said:
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

I still have a question with this. I was out last night trying some landscape/storytelling pictures and was trying to use the knowledge learned in this post to maximize my focus range.

My wife and I were on a bridge, which was casting a shadow of us onto some flat prairie land. Beyond that was a creek, some trees, some housing, and finally the sky/clouds.

So, all I did was (using AF) adjust my focal point to be our shadow, which was about 20 feet away. I then depressed the shutter halfway down to let the AF kick on, and snapped away. Is this simple technique allowing me to capture the maximum amount of focus? Or would I need to do something else to have from 10' to infinity in focus? I was fairly confused about what to do when i was taking the shot.

Thanks!