Focusing issues with Nikkor 24-70mm

[Redgum]

Keep in mind that the DOF is affected by the level of light and the distance between camera and subject and subject and background. Rule of thumb in well lit areas is that the subject matter should be one third the distance from the camera and two thirds from the background. Of course flash will add another element and change the light values again so if possible (external flash) the output should be lowered to act as a filler, not a primary source.
If you don't have total control of light in these situations you may always have problems.

[kiwi]

I'm a bit confused red, dof isn't affected by light is it if all things re settings remain the same ?

[N*A*M]

assign the AE-L/AF-L button to AF-ON, use continuous focus drive, center single AF point

then to use this technique: half press shutter to meter, obtain focus lock holding the AE-L button, let go of AE-L button when you've got focus correct, recompose your shot, fully depress shutter to take the shot

[kiwi]

I don't uses focus recompose for party snaps as youth almost guaranteed that either you or they move enough to change focus between the time taken to compose and shoot

At the need of the day you need tsp practice and find a method that works for you

[Redgum]

I'm a bit confused red, dof isn't affected by light is it if all things re settings remain the same ?

Sure is! Kiwi, just think about the aperture you're using, usually wide open. Set up a shot then simply drop more light onto the background and watch the effect. In film work the DOP (Director of Photography) often sets up DoF for dramatic effect and that mostly centres around adjusting light. Same with digital stills. Also one of the reasons we use filters externally to achieve good DoF.

[kiwi]

I don't get that really, technically dof I thought was simply to do with focal length and distance to object...are you talking about bokeh ?

[Redgum]

I don't get that really, technically dof I thought was simply to do with focal length and distance to object...are you talking about bokeh ?

The other element to DoF is aperture. The Wikipedia description may help you a little...

In photography, bokeh (pronounced /boʊ'kɛ/) is the blur,[1][2] or the aesthetic quality of the blur,[3][4][5] in out-of-focus areas of an image, or "the way the lens renders out-of-focus points of light."[6] Differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing to the eye, while others produce blurring that is unpleasant or distracting—"good" and "bad" bokeh, respectively.[1] Bokeh occurs for parts of the scene that lie outside the depth of field. Photographers sometimes deliberately use a shallow focus technique to create images with prominent out-of-focus regions. Bokeh is often most visible around small background highlights, such as specular reflections and light sources, which is why it is often associated with such areas.[1] However, bokeh is not limited to highlights, as blur occurs in all out-of-focus regions of the image.

[MarkChap]

I don't follow this, I think there is a conflict in terms.
DoF is controlled by the focal length, aperture and distance to subject, is it not ??
Yes, light, or more so the amount of available light, will partially determine what aperture you use, but it doesn't effect the DoF if shutter speed is used to control the light ??

Bokeh, or the aesthetic appearance of the out of focus area, would be affected by how much light is hanging around, but not how much out of focus it is, in the first place

[kiwi]

Yes, I should have added aperture

What I dint get I'd that dof would change based on the background light if aperture, distance to object and focal length remains constant....I do understand bokeh would change

[kiwi]

Oh yeah, oops, what mark said