Small Aperture and Auto Focus?

[stephenoachs]

So here's a question that comes to mind as I do more landscape photography -- Im using a small aperture, in the range of f16-f22, to capture detail across an entire scene. I frame my shot, choose a shutter speed that will capture enough light, then focus. Rather, the camera's auto focus kicks in. My question is:

- Am I better to use manual focus?
- Am I skewing my frame focus, even at f-16+, by allowing auto focus to choose an area (or areas)?

I'm shooting with a Canon 30D & 10-22mm, with 9 AF points and am not aware of a setting that forces all AF points to select. Am I missing something?

[alexphotos]

At f16 or f22 you could be off focus a bit and you would not see it due to the big deep of feild.

[agroni]

I agree with Alex that it does not matter that much where focus. I believe that from f8 everything is quite clear and the DOF is almost infinite.
My only advice is for shooting at this F-stop, to use a tripod or a monopod, since sometimes you have to use a slow shutter which might introduce some blurred effect which is not wanted of course. It happened to me before!

[halesr]

An off-camera shutter release can also be helpful to avoid shaking the camera. I read somewhere recently that with digital cameras f11 is about as high as you would need to go. Will try to find the reference.--Rene

[stephenoachs]

Thanks for the input -- yes, I always use a tripod and a shutter release cord -- in some cases I use the mirror lockup feature.

So are you all saying you use auto focus and where the focal plain ends up really doesnt matter, as long as I'm f11ish +?

[dougj]

The 30D will begin to experience diffraction at f/11, this will reduce the image acutance, or sharpness. The smaller the aperture from this point onwards, the lower the image quality. I suggest you use f/11 as your smallest aperture for landscape work, f/8 is probably a better choice IMO.
http://www.cambridgeincolour.com/tutori ... graphy.htm

The Depth of Field for the 10-22mm lens on the 30D at f/8 is quite deep/wide. At 10mm with a focus point 20ft from the camera, the DOF is 2ft to infinity. Here is a website that you can use to calculate DOF with various focal lengths, apertures, etc.
http://www.dofmaster.com/dofjs.html

Lastly, you’ll see “hyperfocal distanceâ€

[stephenoachs]

Doug, this is exactly the type of information I was looking for. I had not found these links in my searching -- many thanks!

[dougj]

I'm glad this is useful.

I'm somewhat lazy and generally shoot landscapes handheld in daylight, using the hyperfocal distances if I want some of the foreground in focus. If not, I simply focus on any part of the far image.

Keep an eye on the shutter speed as smaller apertures require longer exposure times and camera shake is a consideration. As others mentioned a tripod will help a lot if the shutter speed is long.

This works for me, others may have better suggestions.