Portrait DoF rule of thumb

[surfg1mp]

I am struggling to work out what Apertures to use for various outdoor portrait shots. By this I mean, is there a rule of thumb for setting apertures for different numbers of subject. Say one subject, then two, then three and so on. Id obviously like to have say both subjects in focus but blur the back ground nicely.

I have heard of the sunny 11 rule where on a sunny day you set the aperture to f/11 then on a cloudy day set it to f/9. Does this apply to outdoor portraits.

Your help with this will be much appriciated.

[Gidders]

I don't see that the number of subjects affect the dof ... assuming they are all in the same plane. If they are in a line away from you then your dof needs to cover the spread from the front to the back. You dof is dependant on four things:-

1. your camera sensor size
2. the focal length of your lens
3. the aperture
4. the camera to subject distance

Have a look at http://www.dofmaster.com/dofjs.html Also the amount of blur of the background depends on how far behind your subject(s) it is - the further behind, the more blurred.

The rule you are referring to is nothing to do with portraits per se but its a way of estimating exposures out of doors without a light meter and of course ISO setting & shutter speed come into play here - have a look at http://en.wikipedia.org/wiki/Sunny_16_rule With the inbuilt meter in your camera & using one of the metering programs (spot, centre weighted, pattern etc) in conjunction with exposure compensation if necessary should give you far more accurate results

[Alex1994]

Hi there

There is no rule of thumb, but if you're lucky you'll have a depth of field preview button on your camera which shows you what dof the chosen aperture will give you.

There is no general rule for the reason that dof also depends on focal length - longer lengths give you less dof. What I would do is stick to the largest 2 or 3 aperture stops on the lens.

The best way is to go to dof master (the site that Gidders linked) to work it out.

The sunny f/16 rule is something completely different - it's a rule of thumb for calculating exposure when you don't have a light meter. Your DSLR doubtlessly has a light meter so you can leave that well alone. With outdoor portraits in bright light requiring a shallow DoF and hence wide aperture you'll have to reduce the shutter speed or use an ND filter which will reduce the amount of light entering the camera.

[surfg1mp]

Thank you for the advice guys. I have had a look at the dof guide before and it went straight over my head, maybe i need to study it some more.

[Craftysnapper]

There is no rule of thumb, it tends to come naturally after a while.

Saying that for formal portraits they used to use polaroid proofs in the film days to check exposure and dof.

In the digital age you already have a built in proofer in your LCD screen, take the shot magnify it to check if the subject/s are in focus and background out of focus and adjust your aperture if and when as needed to get the result you want.