A Primer on Depth-of-Field

petercox · 08-11-2009 10:15pm #1

Hi folks -
Thought you might find this interesting. It's an article I wrote for my October newsletter, and just now putting on the main site.

If you've ever had difficulty understanding depth-of-field and how to control it, or even why the aperture has an effect on it, my primer on the subject will be of use to you.

I'd love to hear comments on it. For those of you who are already familiar with the subject, this is a somewhat simplified view of it. The idea is to give the total novice a basic grounding in the subject without running for the hills.

Cheers,
Peter

Borderfox · 08-11-2009 11:15pm

Seems pretty good at explaining the subject Peter.

CabanSail · 08-11-2009 11:49pm

Very well explained. Thanks for that.

Micilin Muc · 15-12-2009 9:16pm

I couldn't help but notice the incredible depth of field in the profile photos of the X-Factor finalists. I'm starting to believe that they don't contain real depth of field, but rather are photoshopped images.

What do you think?

Fajitas! · 15-12-2009 9:21pm

Nope, it's quite realistic.

Check out the 85mm 1.2's and 1.4's - Or even the 50mm 1.0's

Micilin Muc · 15-12-2009 9:26pm

Fajitas! wrote: »

Nope, it's quite realistic.

Realistic as in the fact there is such a large aperture, or that the images are realistic? I think the images are quite disorientating to be honest!

Fajitas! · 15-12-2009 9:33pm

Well... Both!

Realistic as in, an aperture as large as 1.2 or 1.0 will provide DOF like that, and realistic as in the images look quite untouched - Usually, images coming from that kind of background would have rather a lot of retouching.

petercox · 15-12-2009 9:33pm

Regardless of how you feel about the technique, the shallow depth of field in those images is the natural product of a very wide aperture.

Peter

AnCatDubh · 15-12-2009 9:36pm

extreme bokeh (opposite side of the depth of field coin) is very doable even with poor lenses (albeit quality will suffer) if you adjust the aperture downwards in value (open the aperture), the focal length upwards (lengthen the zoom) and the reduce the distance to subject (get in there closer). This is the first major difference you will notice in moving into the SLR world.

The above images are most likely photoshopped to some extent i.e. false like everything else on that bloody show but that's a rant for another day

But its not inconceivable that a very shallow depth of field was used at least in part. Particularly with Lucy's image where the right eye (left of the image) is to my eye sharper than the opposite eye. A very narrow depth of field with head ever so slightly tilted could achieve this aesthetic in camera. Check out dofmaster for examples and play with the settings to see how much depth of field you get (in focus v out of focus).

Still - like the xfactor itself I think the whole show is photoshopped

Fajitas! · 15-12-2009 9:50pm

Naw, they've left too many other blemishes in tbh. You wouldn't go to the lenghts they'd have gone to getting those looking that natural and leave out the basics.

ThOnda · 15-12-2009 11:03pm

They look optical, not photoshopped. Look at her eyes and then her shoulder - they are in the same focal plane and therefore focused.
Sell a kit lense and get 50/1.8 -> new world will appear in your viewfinder ;-)

stcstc · 15-12-2009 11:16pm

peter

in the article, which is very well put together by the way

you say that focal length affects depth of field, this isnt quite accurate is it. its magnification that affects it.

ie if say a 100mm lens and a 400mm lens have the subject at exactly the same size within the image, the depth of field is the same. the perceived change in depth of field from a long lens is generally to do with how much magnification is going on, or am i misunderstanding you

Rb · 16-12-2009 12:49am

AnCatDubh wrote: »

extreme bokeh (opposite side of the depth of field coin) is very doable even with poor lenses (albeit quality will suffer) if you adjust the aperture downwards in value (open the aperture), the focal length upwards (lengthen the zoom) and the reduce the distance to subject (get in there closer). This is the first major difference you will notice in moving into the SLR world.

The above images are most likely photoshopped to some extent i.e. false like everything else on that bloody show but that's a rant for another day But its not inconceivable that a very shallow depth of field was used at least in part. Particularly with Lucy's image where the right eye (left of the image) is to my eye sharper than the opposite eye. A very narrow depth of field with head ever so slightly tilted could achieve this aesthetic in camera. Check out dofmaster for examples and play with the settings to see how much depth of field you get (in focus v out of focus).

Still - like the xfactor itself I think the whole show is photoshopped

Obviously not enough to stop you watching considering you know their names

Thanks Peter.

A Primer on Depth-of-Field

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