DOF with Wide Angle Lens question

My widest angle lens is 17mm using a FF camera. The hyperfocal chart shows that at f/8 at 17mm I only need to focus 5 ft in front to get focus from 2 feet to infinity. At f/11 I need to focus 3 feet in front to get everything from 1.5 feet to infinity. My question is this: is there ever a reason to go above f/11 with wide angles in order to get max. DOF? Since they say the "sweet" spot of a lens is at f/8-f/11, what would be the point of going above this since you can get such great DOF at this aperture?

I'm curious as to everyone's thoughts on this.

Well any time you focus, there's really only one plane parallel to the sensor/film that's actually in perfect focus. Everything else slowly gets blurrier as you move away from this plane. The DOF is calculated assuming that the amount of blur at other distances isn't noticeable in prints of a particular size. It's a measure of what is acceptable by some standard definition. It doesn't really mean that everything is in perfect focus.

So you still might not have focus as good as it can be for the parts of a particular image that are important - hence needing a higher f-stop. Also, the larger the print you want to make, the more important the actual location of the perfectly focused plane becomes. If you are hyperfocal focusing and something in the near FG is important, it won't be maximally focused despite falling inside the stated DOF. Whether this matters in prints or screen images depends on the subject and image size.

The other reason to go higher in f-stop is to lengthen the shutter speed, if that's needed. In those cases, though, you may also run into a slight overall softening of the image due to diffraction. Again, the output image size will determine whether or not that's actually a problem.

All that being said, depending on your particular images, it's likely that you can shoot in that aperture range almost all the time.

I generally avoid anything much over f11 anyway, due to problems with diffraction.


Kent in SD

It depends a lot on how you shoot. I do a lot of belly flop shooting with wide angle lenses, actually laying down on the ground with the foreground mere inches in front of the lens and the FOV extending all the way back to the horizon. I try f/11 but will go to f/16 or even f/22 at the risk of diffraction, but on behalf of the extreme stretch of the DOF.

I've attached a quick laptop edit of a mediocre photo to illustrate the style. The extreme foreground is probably no more than two inches from the lens.

Nikon D2X, Nikkor 12-24mm

Thanks. Good question followed by good info. Thanks for the "mediocre" photo to illustrate the point, Hank. I still really need to work on hyperfocal distance in my shooting.

For those looking to get REALLY close focus (a few inches) out to infinity, there is another alternative - blending several photos together that have different focal planes. The newer editions of Photoshop have a version of this that is OK. Here's a link to a discussion of how to do this:

http://davidsaffir.wordpress.com/2009/12/27/blending-images-in-photoshop-for-increased-depth-of-field/

I'm told by one of the editors of this site that Helicon Focus works much better. It's used by some that shoot macro as well as landscape to get better DOF. There seems to be a 30 day free trial version available at: http://www.heliconsoft.com/heliconfocus.html I plan on trying it in the near future to see if it helps.

That's good to know Wick. I'm disinclined to get too dependent on post processing (for the time commitment), but fallback would be great for circumstances when comparable results are impossible in-camera.