What’s the Best F-Stop?

“What’s the best f-stop?” This is the second most commonly asked question that arrives in my inbox. It’s no surprise—depth of field (DOF) is a mystery, since you really can’t see it in the viewfinder of your DSLR. No matter if you’re just beginning or a seasoned pro, this is a question you should always ask yourself when you put that camera to your eye. (In fact, you should be asking that before then.) It’s not a question you should be asking Moose. Not that I don’t know the answer, but I only know the answer for my own photography. Since it’s your storytelling, you need be the judge of what the best f-stop is.

But how do you get to that point, come to learn, and to own the right lens with the best f-stop for your photography?

Editor's Note: This is a guest blog post by Moose Peterson.

To save you some time, the following discussion will not include what is so often included in a discussion on depth of field. There will be no charts, no scales, no measuring tapes, no lens analyses, no hyperfocal, no theories—only realities. That’s because photography is a visual way of communicating, a means of telling a story, and all great stories have a central character. In photography, we call that the 'subject.' Like all great storytelling, in photography we must set the stage for that subject, while at the same time making the subject stand out for our audience to connect with. That’s how I look at DOF, so if that intrigues you, read on!

The Thought Process

Before the camera goes up to my eye, the question that runs through my mind when I’m getting ready to go 'click' is, “What’s the subject?”

That has to be known from the get go, and with that knowledge a couple of things happen. When we know what the subject is, the rest of the storytelling and the elements we want to include and exclude become clear. With that knowledge we can determine the exposure, which directly affects DOF. With that knowledge, we also know what lens we want to use (or at least try at first). And with that knowledge we realize we are not in charge, but rather the subject is. We just dance around it to tell its story.

Putting this into practical working terms, let's take a look at this photograph of a Grizzly Bear, going after jumping salmon (Brooks Falls, AK).

So what’s the subject: the bear, the salmon, the act or the scene our subject? 

If we say the bear or the salmon, then freezing the action is essential, because our subject needs to be sharp for the viewer to connect with it. As soon as you make that commitment to the subject, then your DOF has been predetermined for you. Since the bear is out in the water, you have to use a longer lens to get a decent image size—in this case a 400mm. The fastest aperture available is an f/2.8, and at this working distance that’s plenty of DOF, since you're focusing so far out. If you want to gain two or three inches more DOF, which is all you’re going to gain, you can go to f/5.6 (I wouldn’t though because of the subject). But the best f-stop in this scenario was out of our control.

Make the subject the scene, then what happens to the best f-stop options? The scene then is the act of fishing, the bear waiting for the salmon to jump. Want to talk about time passing? Nothing is as effective as blurred water. If you want to blur the water, then you need to shoot at a slow shutter speed. The slow shutter speed means your lens's aperture is closed down all the way to f/22 or f/32. Again, the best f-stop has been decided for you.

How Then Do You Gain Some Control?

How much is and isn’t in focus in your photograph is one of THE most important ways we have of visually communicating. This means we need to take some control over the photographic process. Here lies the challenge! In my own style of photography I do this by two main means: lens selection and background.

If we look at the two images of the Catbird, the image size is pretty close, so the physical distance of the subject from the lens is similar. Yet one background is busy and annoying and the other is clean like a water painting.

Since both were shot with a 600mm VR with TC-17e attached and shot at f/8, where is there such a big difference in the background? It has to do with how far away from the background the subject is! This is how I came up with my mantra long ago, “Get close physically to the subject and use optics to isolate.”

Then to gain some control over how much is in focus, you move the subject either closer or farther from the background. A perfect example is the photos of the T-50 “Bamboo Bomber,” which is shot at the exact same f-stop and shutter speed, but the physical distance from the background is radically different: 100 feet compared to 1000 feet!

Okay—you’re saying in theory you can move a subject like a plane or person to gain some control, but you can’t ask a bear to move left or right or pick up a boulder and move it. What then?

If you asked those questions, I have no doubt you’ll master the best f-stop question. That’s because you are asking questions and when you ask questions, you find answers (just be forewarned for every answer you find, five more questions will pop up). Let’s start with a rock or to put it more romantically, a landscape photo (the story of rocks). We still have to deal with the two main characters in our storytelling, the subject and the background. With landscapes, we should probably ask “What do we want to say?” more than “What’s the subject?” in the beginning. But what the finished photograph must say is, “You need to be here” and not “I was here.”

At the same time, we need to use physical elements in our landscape photograph to give it visual depth. In my book, you must have a foreground, middle ground and background in your photograph—especially landscapes. These three planes are physical ones and have to be present, but just how much of each is in focus is up to you, the storytelling you’re doing and the f-stop you select to make it all happen!

Looking at two landscape images (big rock at Alabama Hills, CA), both photos were taken with the same lens with the same f-stop. The one image though has only two planes, a foreground and a middle ground. Some might argue the sky is the background, but those wisps of clouds don’t count for much. When you compare this one to the other image where you can see the Sierras in the background, there is a greater feeling of spatial depth without changing the f-stop. In this case, the lens is a 16Fish and the f-stop is f/2.8.

Now critters are a challenge, there is no doubt about that when it comes to the best f-stop. My own personal rule of thumb is:

- Birds are always f/8

- Small mammals are f/8

- Big game, whatever I can get away with.

With that said, these are starting points. I’ve already shown two examples where this didn’t hold true, the Grizzly Bear. While I could change up the storytelling (which wasn’t done by predetermining the best f-stop) I still had no control over the subject. If there is a trick or magic to the best f-stop and storytelling with critters, then it’s this.

Time! This means that you must wait for the right moment to go click. The bison photos are a good example of this. Both images were taken with a 400mm (400 f/2.8 & 200-400mm VR2) and both required waiting for the critter to move. The bison cow & calf shot taken in Custer State Park, SD is one example. It was shot minutes before they were amongst the herd, so any click and the pair would have blended right in. That’s because the herd was so physically close to the background. Given a few minutes and they wandered off and only had the sweep of a spring green carpet for a background. This rightfully implies that being situationally aware is very important in any genre of photography. The cow on the ridge in Yellowstone is another prime example of being aware of your surroundings. Moments beforehand, it was in a forest, a world of busy branches and yuck. Looking at the direction it was heading though, it was obvious it would be on that ridge line and with the ridge in the background being a mile away, while a pretty monochromatic photo, she pops right out! And this photo was taken at f/16!

If that photo was taken at f/16, why are the mountains a mile away in focus? Because they are a mile away! If available, I could close the lens down to f/64 and they wouldn’t be in more focus. The bison might be sharper (trade off with slower shutter speed associated with small aperture) but the physics of lenses dictates that those mountains will be out of focus. You must have all of this in your head and heart as a photographer telling stories. There is no chart that is going to teach you this.

Folks and Light

I’m not about to tell you I’m an expert here; because I’m not. But I do photograph people; I have done so for a long time and I think through the process the same way for a rock, rabbit or aircraft.

“What’s the subject?” and “What’s the story?” is what I always ask myself. With most portraits we again have some control of subject and background, which makes the best f-stop a more realistic question with a real answer. Of course that one thing I haven’t really talked about, which is the cornerstone of great photography really comes into play now, light. Let’s start with just ambient light.

Here is one of my favorite images of Donald in the NM Pen. You’re working in a jail, the only way someone will know that is by including the bars. But those vertical lines can grab a viewer’s mind’s eye and never let go. 

Want to go wide to include the entire scene, but want a narrow DOF? The answer is the 24mm f1.4 shot at f/1.4. This is a very narrow band of focus, so narrow that while Donald’s right eye is tack sharp, the left one is just sharp. Why don’t you pick that up? I’m underexposing, which not only brings a real mood to the photo, but also makes the shadows blacker—therefore tricking the eye to seeing things sharper. The light is all natural coming through an exterior window with a simple TriGrip, bouncing it back into his left cheek. The best f-stop again was decided for me by the subject, light and situation, but it was critical to have that 24mm f1.4 to make it all come together.

Move on to Stu working on the B-17G “Sentimental Journey” in Mesa, AZ. To tell the story, all I had to include were two elements, Stu and the aircraft in the background. If I went wide, we would have seen more of Stu and the B-17G.

But do we need to see more of both to tell the story? It’s Stu’s facial expression and hands that are the subject, the rest of Stu’s body and the B-17G are simply the background for those two elements. To accomplish this photo, I had to move back physically, grab a longer lens, in this case a 70-200mm VR2 and shoot wide open at f/2.8. And if I hadn’t had gorgeous diffused light, the whole photo would never have come together.

As soon as you bring flash into the equation, your f-stop again can become predetermined for you. In the photo of Tre looking out the truck window, I had to put both her and the reflection on the same film plane to shoot at f/4. I needed that f-stop because I was shooting with just one SB-900 through a TriGrip and needed to balance that with the fading sunset. As soon as you start trying to blend flash with ambient light and that ambient light is the setting sun, you are scrambling! Your f-stop determines the flash exposure, shutter speed as to be used with that f-stop that is carved in stone because of flash to expose for the sunset and then there is the DOF.

What is the best f-stop? A lot of times it’s whatever the storytelling process has selected for you.

Remove shooting into the sunset and then you gain a little control back for your f-stop setting. Here, we’ve put Morgan into a junk yard truck in MT and lit her with an SB-900, firing through an EzyBox. The flash is gelled with an 81a to match the quality of light from the fading sun. In this case, we could select whatever f-stop we wanted (f/8) and then change the shutter speed to make the sky stormier and the colors more vibrant (so underexposed by two stops).

Okay, What’s the Best F-Stop?

There is no “best” or “magical” f-stop, just the one that tells your story your way.

In the beginning, there is no way you can know this, so don’t beat yourself up that you don’t. You start to learn what’s best for you by asking the question, “What if?” “What if I used this f-stop or that f-stop, what happens to my photo?” Take a photo of your hand (our portable clacker), then shoot from wide open to all the way closed down and then take a photo of your hand again. When you get back to your images, you’ll see this series of “What ifs” and you’ll have the meta data telling you the f-stop for each image. Look at the images and in this exercise, what was the best f-stop FOR YOUR photography in THIS INSTANCE? Copy those images to a folder called, “What If” and go back and look from time to time. That’s how you learn for YOUR storytelling what the best f-stop is for YOUR photography!

Photography is such a grand and romantic pursuit as we tell the story of the great fortune we witness with our camera in our hands. When you free yourself from worrying about some of the rules some suggest you should worry about, you’d be surprised how much your photography grows and becomes an extension of who you are. Give yourself time, give yourself permission to fail and to grow and I guarantee you will quickly have the answer to the #2 question coming to my inbox. You will know for your photography, what’s the best f-stop!