Shallow DOF not so shallow?

[knightrider]

I follow Sam Javanrouh's daily photoblog because he takes some really nice photos, and because he always includes the camera settings used, which is really useful to learn from. Today's image confused me, however.
I've got the impression that f/4 is a pretty fast aperture, and should give a fairly shallow depth of field. But in this photo, shot at f/4, the depth of field is seemingly infinite. Both the rigging on the yacht in the foreground and the buildings in the background are in focus.

See Photo Here

Have I misunderstood the use of aperture in creating a depth of field, or is there something else in the way this photo has been taken that means it is so?

Thanks

[Skyman]

If you look at the EXIF data for that picture the answer is in the choice of lens: Sigma12-24@12.

A wider lens will generally have a greater depth of field at a given aperture than a longer lens and for the 5d (full frame sensor) 12mm is indeed very very wide, so it stands that the depth of field at F4.5 isn't going to be nearly as shallow as you might think. also by carefully controlling the focus point (probably using the lenses natural hyper focal distance) the maximum possible depth of field can be obtained.

[Greg McCary]

You can get sharp pictures from front to back with any F/stop. Before digital lenses a technique called hyperfocal focusing was used. With an older lens with manual settings you simply placed the infinity mark on the f/stop number you were shooting and then the distance scale would give you a minimum focus distance. But with modern lenses with no marking you simply focus 1/3 the way into the shot. Here for instance the focal point for me would have been the back of the large boat. But with all of that said most lenses sweet spot is around the mid range f/8 or so. But with these modern digital lenses they all seem to be super sharp to me.
As Skyman pointed out the wider the lens the better. Your minimum distance will be shorter and faster shutter speeds possible. Personally I try and stay around f/8 or f/10 if at all possible. Depending on what I am shooting. If I am shooting just a picture of an old wall or window and it doesn't require great depth I will some times shoot more wide open. Check the link if you want more nut and bolts on the subject.
http://en.wikipedia.org/wiki/Depth_of_field

[Ron Kruger]

Excellent info, explained well, Greg and Skyman.

[mjs1973]

Knightrider,

Please don't post other photographers photos. If you want us to look at someone else's photo, please post a link to it.

[knightrider]

So a combination of have a full-frame sensor, very wide focal length, and optimum focusing distance culminated in f/4 delivering a very deep depth of field?
I have alot to learn...start with that wiki article on DOF and keep going

@mjs1973: Sorry, didn't know.

[Greg McCary]

Here is an example of a wide lens. This is a Voigtlander 15mm lens I use on my M6. The lens doesn't couple to the rangefinder so I have to guess focus distance. But the lens has such a great DOF you almost never miss. Basically as you see here if I am going to shoot at F/8 I put the infinity mark on F/8. On the other side of the lens look on F/8 and you can see that .5 meters is the minimum focus distance to infinity. If I were to move the infinity mark to 5.6 or 4.5 the minimum distance would increase and at f/16 my minimum distance would be less than .3 meters. Large focal lengths have longer minimum distances.

[Photo-John]

knightrider-
I went ahead and replaced the photo with a link. Please forgive me for editing your post. It's not something I like to do. But one of the things we are pretty strict about is not posting other peoples' photos on the site. Since this is a serious photography site, we consider photo ownership sacred. It's fine to link to someone else's photo - in fact, I encourage it. The more we see, the better. But we never want to have any confusion over who actually took a picture.

Thanks for understanding and welcome to the site. Always happy to have an enthusiastic, open-minded new member

[knightrider]

Since this is a serious photography site, we consider photo ownership sacred. It's fine to link to someone else's photo - in fact, I encourage it. The more we see, the better. But we never want to have any confusion over who actually took a picture.

No worries, and I'll bear that in mind next time I want to show a photo. Sorry 'bout that.

Thanks Greg, that explains alot of it