aperture guidelines for number of people

[cindynemm]

I dont know if I drempt this or not - but somewhere i think I read about some "general" guidelines to setting your f stop according to the number of people in the picture. This is what i think I remember.

As a general rule - you should double the f stop for the number of people in the pictures. Example: If 4 people are in the shot - f stop = 8
If 2 people are in the shot - f stop = 4
1 person - fstop = 2.0

did I dream this or is there any validty to this theory?

Please help - my daughter wants me to take some family pics (family of 4) and I'm a nervous wreck about my settings.

[Rentham]

I've never heard that. I think there are too many variables at play. Focal length, sensor size, distance to subjects, configuration of subjects, etc. A group of 4 shouldn't be a problem under almost any circumstance I can think of. If in doubt, shoot wider angle and stop down your aperture - both of which will give you more DOF.

[ceremus]

You can always plug your aperture, focal length, and distance to subject values into a DoF calculator and see if your DoF is deep enough. If you have a smartphone there's probably a DoF calculator app you can run. I know they're out there for iPhone/iPad and Android devices.

[wulf]

Forget about the number of people - it is a confounder (I've been sitting in a stats class all day so my head is swimming with technical vocabulary ... it just means that aperture <---> people is a false relationship and confuses things).

The important value is depth of field and that is based on focal length, distance of the subjects from the camera and aperture. As suggested, use an online calculator (do you need a link?) to find out how those things work together to give you a range in which your can expect your photos to be sharp.

Also, the camera doesn't care whether you photograph people, chairs or trees. One thing that will help (especially if just playing with numbers seems too daunting on its own) is to practise with inanimate objects and get a feel for what depth of field means in practise. For example, if I wander round my garden with my 50mm lens, I know I can take shots of plants 15' away with a fairly wide aperture but if I am only 3-4' away I will need to stop down to a narrower aperture (and compensate with slower shutter speed and / or higher ISO) unless I want a very narrow depth of field to just bring out one feature.

Wulf