Understanding Exposure ?

[dbiggs]

I have read 2 books now by Bryan Paterson "Learning to see Creativatally" and "Understanding Exposure" Revised adidtion and I have a couple Questions. From most of the examples in these books he rarly shoots at anything below F11 and usually like F16,f22 or f32 if this book is updated for digital how do you do this without defraction starting to crep in. The second question is aabout infinity and DOF on page 57 he is shooting a landscape at a "how cares DOF at f 8 because everything is beyond the infinity. I have always been unclear about this situation if everythig in the fram is beyond infinity focus point does the Av have no affect on what is passed the infinity point and just affect what is in front of infinity.

[Jman13]

If you are shooting a landscape, and everything in the frame is at or beyond the infinity focus point, there will be enough depth of field at any aperture to have the entire frame be within the focus plane.

There are three things that affect the DOF in any given shot.
1) Lens Focal length. At the same subject distance, the longer the focal length, the less the depth of field.
2) Aperture. At the same distance and focal length, the larger the aperture, the less depth of field.
3) Distance to subject (where you focus). At the same focal length and aperture, the closer you focus, the less depth of field.

So, the minimum depth of field for any lens is at maximum aperture and minimum focus distance. The maximum for any lens is at the hyperfocal point and minimum aperture. (The hyperfocal point is focusing at a distance, that when combined with your aperture and focal length, makes the far limit of focus infinity...).

As far as him choosing small apertures a lot...yes, there are diffraction effects at small apertures, even on film. However, often times in landscape photography (and other times), the effects of diffraction are minimal compared to the need to get your scene in focus from foreground to background. That's up to the photographer. HOwever, if you're focusing on a large rock right in front of you, and the trees in the distance need to be sharp too, sometimes your only choice is to deal with diffraction and choose f/22.

DId I help or confuse you more?

[dbiggs]

I still am not clear I guess I'm slow or something. Lets use this examplw when I uae my 12-24 lens I find that even with the Av wide open F4 everyuthing is always in focus it seems to have a large DOF but infinity is at like 10 feet or 3M. So is everything past 10 feet in focus always in focus at infinity and as I stop it down the things between 10 feet and closer going to be in focus as well am getting it?

[Jman13]

yes, you're getting it to some extent. Wide angle lenses have a LOT of depth of field unless you're focusing extremely closely, which is why you're seeing what you're seeing. Stopping down at infinity focus will give wider DOF, and bring your sharpness closer. However, if you want more in front of you to be in focus, the better way to do that is, focus on the close object, then stop down from there to get the background more in focus. If you're focusing on something 12 inches from the lens, and you want everything from front to back in focus, you'd probably have to focus behind the object a bit, and stop down a lot. I'm pretty sure the Understanding Exposure book has something on hyperfocal distance...this is the point you would focus on if you want the absolute maximum depth of field from front to infinity.

[Jman13]

Oh - and here's a neat tool to play around with to understand what your depth of field will be for any lens, any aperture, and any focusing distance. It should help you get a handle on what's happening. Below the calculator is a good explanation of depth of field and hyperfocal distance:

http://www.dofmaster.com/dofjs.html

Using this calculator, you can see that on your camera, at 12mm, the hyperfocal distance is 6.26 feet when the lens is at f/4. That means if you focus on something 6.26 feet away, everything from 3.1 feet to infinity will be in focus. Pretty cool, eh?

[Lester Wareham]

I have read 2 books now by Bryan Paterson "Learning to see Creativatally" and "Understanding Exposure" Revised adidtion and I have a couple Questions. From most of the examples in these books he rarly shoots at anything below F11 and usually like F16,f22 or f32 if this book is updated for digital how do you do this without defraction starting to crep in. The second question is aabout infinity and DOF on page 57 he is shooting a landscape at a "how cares DOF at f 8 because everything is beyond the infinity. I have always been unclear about this situation if everythig in the fram is beyond infinity focus point does the Av have no affect on what is passed the infinity point and just affect what is in front of infinity.

For a 1.6 crop camera difraction starts to soften the shot at f16 although you might accept this to get a bit more DOF if your are desperate. If you do macro work the diffraction limit comes earlier for the set fstop (rather than effective) depending on the amount of magnification.