D90 focusing question

[Derrel]

Here's an article about a group portrait focusing and composing technique that probably nobody under the age of 40 has ever heard about, but which has been around for over 100 years.

Group Portraits by Don MacGregor, Tamron USA

 

[Tbini87]

Here's an article about a group portrait focusing and composing technique that probably nobody under the age of 40 has ever heard about, but which has been around for over 100 years.

Group Portraits by Don MacGregor, Tamron USA

Thanks Derrel. Quick and easy read while very helpful. I think we will certainly be using an fstop around 4 instead of 2.8 with groups from now on. The string idea is also great if we are really set on using a very shallow DOF with a group.

The article didn't really mention the difference in DOF when using different focal lengths. Isn't an 85mm prime going to give a lot shallower DOF compared to a 35mm prime when at the same aperture? So shooting an 85mm lens at 2.8 is going to be a lot shallower DOF than a 35mm lens at 2.8 right? I had never really thought about that until we started shooting with 2 different bodies with two different focal lengths on each one.

 

[Derrel]

In ordinary (non-macro) photography, depth of field depends upon distance from the camera to the subject to a very large extent. The size or image magification also plays a role in the amount of depth of field; an 85mm lens shot at f/2.8 at 10 feet will give a shallower depth of field than a 35mm lens shot at f/2.8 at 10 feet--BUT, the telephoto will produce a fairly large image of a person's head and shoulders with a narrow angle of view behind them, while the 35mm lens will give a smaller image of the person, with more of an angle of view behind them.

In the way that most people commonly use lenses, with wide-angles being used to include wide angles of view and SMALLISH renderings of things, yes, a wide-angle, 35mm lens at f/2.8 will show more depth of field than an 85mm used to take a tight, magnified "telephoto" type of shot. However...if one decides to get really CLOSE with the 35mm lens, to create the same,identical sized head and shoulder portrait shot with the 85 from farther away...then the 35mm lens at f/2.8 will have basically the same depth of field as an 85mm lens shot from farther away...

This is an attempt to simplify things, for brevity. There is also background blur, which is different with telephoto lenses than with shorter lenses. On tightly-framed groups of people, even f/4 might be too wide of a lens opening to ensure that everybody is acceptably in-focus in a larger print; I'd start thinking about f/4.8 to f/5.6 as being the territory where there's a little bit more safety, rather than f/4. Again, DOF "depends", mostly, on how far the camera is away from the subjects.

 

[Tbini87]

Thanks Derrel. Didn't really add in distance subjects are from camera in the DOF equation. Very helpful. 4.8+ it is for now until we really start nailing this whole focus thing down!

 

[classcams]

There are quite a few calcs for DOF on line. A quick peruse will soon bring you up to speed.

 

[KmH]

Lens focal length and subject to backgound distance are factors that also contribute to DOF.

Here are 2 online DOF calculators:

Online Depth of Field Calculator
http://www.tawbaware.com/maxlyons/calc.htm

I prefer the graphic in the 2nd calculator, because it shows the rate focus falls off better.