Aperture, DOF, And, Decisions

Way, way, way back prior to the onset of this winter, during the last gasps of the kind of weather you will find me outdoors, I spent an afternoon making images I typically wouldn't make on purpose. I put aside a lot of the things that have been built-in reactions for a long time. For the most part I reconfirmed why those built-in reactions are built-in at this point. I did make discoveries of the good kind. The kind that cause one to rethink biases. Today I wanted to share a bit of the latter regarding choice of lens aperture and context.

The shot at the top represents something I never ever never ever do. Well, I never do it unless I have some sort of exceptional reason to do it. What is it that I never do but did anyway here? I shot wide open at f/1.4 on a 50mm lens with a relatively flat subject plane. I did a bunch of other stuff here that I never do either but let's focus on that decision regarding lens aperture.

For my own preferred subject matter and how I shoot it the choice of lens aperture typically is more important than some of the other exposure variables like shutter speed. In ample light I can choose any aperture I want. Here I was shooting at ISO 100 and the choice of f/1.4 resulted in a shutter speed of 1/2500 second. I could have easily shot at f/4 or f/5.6 or f/8 or whatever. My reaction here would normally be to choose f/4 or f/5.6 if I were on cruise control. That choice would have the same overall effect but what was in focus would have been at optimal sharpness and detail. I would have reduced the risk of slightly out of focus important elements. I would have no lens exposure falloff, etc, etc.

The choice of f/1.4 bought me nothing of consequence here only risk and lens faults that don't really contribute to this setup. The scene is relatively flat and the limited DOF is hard to discern. Notice the dress looks like it's blowing in the wind a bit. It's not, the air was dead still. I wanted a bit of a breezy feeling so Katya simulated some with movement while I grabbed a shot where it felt a bit breezy. Hence the f/1.4 risk with no upside. Yea, the background is slightly softer at f/1.4 than it would be at f/4 but not in overall effect. Are there reasons to go for f/1.4 in a flat scene like this? Sure there are – like no light and no choice but to introduce that compromise. Another would be someone that needed a bit less detail and sharpness in their skin. An aperture of f/1.4 on a 50mm this close will certainly soften the skin a bunch compared to f/4 with all of the other things that go with that decision but for me they are exceptions.

Let's contrast that shot at the top to a more typical scene where f/1.4 makes far more sense if I want some sort of limited and blatant depth of field effect.

Now we're cooking with gas… At least I'm getting something with that f/1.4 decision. Some blurry background stuff that's quite apparent. I also confirmed here that my general reaction to strongly patterned backgrounds with a lot of contrast like this fits my aesthetic – I hate them. I kinda liked the sun that was popping in and out in the out mode here. I love the couple of red flowers on the left in the deep greens skewed towards blue too. I wish there was a wall full of them… there's not.

Back on point, see how f/1.4 is way different in a scene where there is separation between near and far? I know that all of you already know this in your head but you would be surprised how that intellectual knowing just seems to disappear when a lot of people are in real shooting situations. I wanted to bring this up for that reason as well as a few others that could be considered philosophical or even psychological considerations. Before I get into those I did want to make one point clear regarding aperture, depth of field, and all that; it's not just the aperture choice, it's aperture choice in combination with scene context and especially relative scene depth. I use the word relative because the depth of a scene and how aperture choice renders is absolutely going to be relative scene depth. That the first shot is relatively flat. From my camera position all the stuff is about the same distance away. If I get in really really really close to Katya then her eyelash will be relatively much different in depth than say her nose or her lips, especially if I am shooting down. That's what I mean by relative.

Let's move on to the philosophical and/or psychological factors here. I tend to shoot using manual exposure control and absolutely no exposure automation. I know myself. I need to force the issue to make those choices scene by scene. If I don't force the issue of evaluating things and making conscious decisions then I won't. I know I could make those decisions in programmed auto with auto ISO. I just know that I won't. More accurately I will not make them consistently. I tend to use exposure automation and things like that where they are appropriate… When things are changing really fast. For me automation isn't about "forgetting" to set something and making some sort of horrid error. For me it's a compromise when I don't have the choice. If I am going to make more than one shot of the same scene under the same conditions I much rather force myself to make choices about it every single time.

Food for thought.

RB

blog comments powered by Disqus