A lot of pictures of my kids lately. But with Christmas around the corner… let’s just say family life comes to the forefront in a big way. Truth is I’ve been winding down from work this past week and will be taking a bit of a break for the holidays.
While doing some editing yesterday, I had a chance to listen to the replay of Zack Arias’ Foundations of a Working Photographer on CreativeLIVE. Good stuff. He approached a subject that we often take for granted once assimilated, but that is often veiled in mystery when first starting out: the relationship between focal length, distance to subject and depth of field. When looking to control depth of field, common wisdom usually focuses on aperture: a wide aperture will give you shallow DOF while a closed aperture will get you deeper DOF. So to create that bokehlicious portrait where the entire background goes blurry while the subject stays in focus, just open up that aperture as much as you can and be happy. Which is true. But it’s not the entire picture.
Focal length and distance play a huge role as well. Basically: the longer the focal length, the shallower the DOF and vice versa. Also: the closer you are to the subject, the shallower the DOF. This is important and should guide your choice of lenses in a given situation — f2.8 on a 24mm 20 feet from your subject won’t look much different than f8. Get in closer and that changes drastically. Switch to 200mm at that same f2.8 and it’s a whole other story.
I took the following pictures after dinner last night, just to calm the kids down (!)
They’re sitting on the wooden stairs that lead to my studio. Lighting setup is one SB-900 (B&H) in a small Photoflex Litedome softbox (B&H) placed a little over their head, camera right about three and a half feet in front of them and aiming to the left. The light is obviously picking up some of the wood’s warmth. I shot all of them with the Nikkor 70-200mm f2.8 (B&H) but notice the difference of DOF between the first and second picture: picture 1 is at 200mm f.2.8 while picture 2 is also f2.8 but at 82mm. Not only can you no longer make out the stairs on picture 1, but the zone of focus is pretty much confined to his right (camera left) eyelashes. That’s a major difference in depth of field, all due solely to focal length.
So next time you pick out a lens don’t just think about the zoom factor. Think of focus and the look you’re aiming for.
And image compression…
Darn — that’s another subject.