Don’t be shallow, check your depth of field for sharp shots

by Adam Pawlak January. 29, 2018 512 views
Check your depth of field - no not with a ruler

Check your depth of field - no not with a ruler

In my recent blog post, I was so focused on nailing that shot and writing about it that I was guilty of not following my own advice!

I did not nail the shot in camera. I totally missed checking for the depth of field.

Now if you are new to this and you do not know what this is, it is basically the minimum and maximum distance out in front of the camera that is in focus. You can google search this and get a far deeper explanation but I will explain more below.

In the shot in that post, I simply set my camera up on my tripod and I set focus for a spot in the center of the scene, shown below:

Focus point as captured in Nikon ViewNX2.  Image was shot in live view.

Focus point as captured in Nikon ViewNX2. Image was shot in live view.

Now this choice of a focus point made it so that the wording on the wine bottle was nice and clear, but the grapes and the front of the fruit bowl were really not in focus.

This is because I forgot to properly account for the depth of field in this photo.

This was an easy mistake for me to make because I am usually shooting sports, action and landscapes where the subjects are quite far away from me. In general, the further away the subject is from you, the greater the depth of field.

But when shooting things up close, depth of field is critical.

It is a totally valid technique for setting up your camera so that only part of your still life scene is in focus. In one possible scenario, you could have 3 chocolates on a plate in front of you. The chocolates could be 24, 26 and 28 inches away from the sensor in your camera. You could use a zoom lens or a prime lens and a wide aperture and set your focus so that the chocolate that is 26 inches away is in perfect focus and the ones 24 and 28 inches away are blurred nicely.

But that is not what I was trying to do here. In this shot, I wanted the whole scene in focus.

So how badly did I screw up?

Well, to tell for sure, you really need to use a depth of field calculator to check for this. I no longer have this scene set up, but checking the EXIF data on this shot reveals that the focus distance was 1.68 meters, or about 66 inches away. The EXIF data also indicates that I shot with an aperture of f11 and at a focal length of 100.8mm (I rounded this to 100mm below).

So now you need to go on-line and use a depth of field calculator or download an app so that you can check this right on your smartphone.

If we plug in my camera and the rest of the numbers in at http://www.dofmaster.com, you will get the results shown below:

Settings for my shot

Settings for my shot

From these results, you can see that from the focus point that I selected the plane of focus starts 2.27 inches in front of this spot and extends 2.44 inches behind it. The total depth of field is only 4.71 inches.

At the top of this post you can see a recreation of the shot, with a ruler. The grapes are not shown but were delicious. Same goes for one of the bananas. Hey, I was hungry :-)

Keep in mind that the focus does not drastically fade right at 2.27 inches in front of the focus point, but it deteriorates gradually the further you get away from it. So this explains why the near edge of the fruit bowl and the grapes are somewhat blurry but the orange and most of the lemon looked acceptably sharp.

So how could I have avoided this?

I could have chosen a focus point closer to the front of the fruit bowl, perhaps right on the orange. That would have gotten the whole fruit bowl in sharp focus, and the face of the wine bottle too and most of the plant.

Another thing I could have done is moved the camera back about 3 feet from the scene. This would have increased the depth of field. I probably would have had to zoom in a bit more though to say 120mm. If you plug those numbers in the on-line calculator (shown below) you get a depth of field of 7.93 inches:

An alternative scenario

An alternative scenario

Even without all of this, closer examination would have revealed to the naked eye that the front tip of the bowl and the grapes were not in focus. This is yet further proof that you really need to check your shots right after shooting but before you leave the scene.

But if you are not sure or when you are just planning a shot, a few quick entries on a website or on a smartphone app can give you a very good idea of what your region of sharpest focus will be.

So if you plan to start shooting some still life or anything up close, pay attention to your depth of field and do not make the same mistake that I did.

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