Tag Archives: Depth of Field

Maybe we need to RETHINK how we think about Depth of Field

Maybe we need to RETHINK how we think about Depth of Field

It’s really about Magnification

We know some truths about Depth of Field (DOF). We know there are 3 things (actually 4 but the forth is controversial and not all agree and it would only apply if you switch cameras in between shots)

Anyway, there are 3 things that affect Depth of Field

  • Aperture
  • Distance to Subject
  • Focal Length

We know:

  • The Larger the aperture (lower f/ number),the shallower the Depth of Field
  • The closer we are to our subject, the shallower the Depth of Field
  • The longer the Focal Length, the shallower the Depth of Field

and of course the inverse of all would be true

All of these are facts, all are true. Except sometimes absolutes don’t fit into how we actually do things.

There is no doubt that aperture affects DOF. We really don’t have to worry about that. But the other two, we do. An interesting thing happens and for most of us it is a unconscious thing we are used to doing: When we change focal lengths…we move.

Think about it, You, have a 40mm lens on and you are taking a headshot of someone (The Subject) we use our knowledge and say to ourselves, Oh wait I want a shallower DOF, I’m going to put my 200mm Lens on. OK It’s on, let me just step back so I frame that person the same way…. and I GOT THE SHOT!

But look at what just happened there. We didn’t do one thing, we did two. We changed focal length and we also MOVED. So, we didn’t do one thing that affects DOF we did TWO!

And the funny thing is, they directly counteracted each other so the actual effect was NIL. The DOF did not change.

OK, I know. Prove it

This image was shot with a 40mm lens at f/4, 1/1600, ISO 100 on Camera Flash. The subject (Frosty) was 1’10” from the Film Plane


Using my Simple DOF phone App here is the DOF for the Image























This next Image was shot with a 200mm lens at f/4 1/1600 ISO 100 On-Camera Flash Shot 9’ 2” from the Film Plane


This is the DOF from the DOF App























As you can see, the framing of the Subject is exactly the same, the DOF is the same (sometimes there are slight variations but within a reasonably close amount) Both are 1.71” (Something that can change, depending on the combination of length and distance, is the distribution of DOF behind and in front of the plane of focus)

Now, I also know what you are saying, “Besides Frosty’s size, those two images don’t look anything alike!! ”

Well true, while the DOF is the same we have two wildly different Fields of View between the two lenses. Ah, you say. But Even the DOF does not look the same. Well that is simply an illusion. Since all you are seeing is the background magnified in the second image shot with the 200mm. The so called “Telephoto compression” But if we zoomed in on the 40mm we see the amount of Blur is essentially the same (remembering that each lens has different Bokeh)

This is zoomed in to the background on the 40mm shot

So this shows us a few things. That the DOF is the same but we can use different lenses for different effect. If we were doing an Environmental Portrait we may want to use a 24-40mm lens. Still have the shallow DOF but have a better idea of the environment. The image taken zoomed in to 200mm would be better if you really had a distracting background you wanted to get rid of you could see less of it zoomed in and still maintain a shallow DOF for isolation.

But one trick you can use by going to a longer focal length since it has an “apparent” if not actually, shallower DOF is you can use a Higher f/ stop on your lens for more DOF on your subject (getting their eyes AND nose within the field of focus). But still look isolated from the background

This one was shot at 200mm f/8.0. 1/400 ISO 100 On-Camera Flash from 9’2”

This is the DOF app






















If you look close, we doubled the DOF and put more of Frosty in Focus but still had him isolated in a shallow DOF

Frosty is about the size of a Human Head. So you can see how shallow the DOF would be if you were shooting that tight on someone’s head. If you moved back in both examples (less Magnification)to a full body length the DOF would be a lot deeper. If you increased the aperture you would get more in focus, decreasing the aperture would yield less DOF (shallower)

So, what is the take away here?

The more an object fills the frame, the shallower the Depth of Field will be

When we frame a subject equally regardless of focal length or distance, it is said they have equal Magnification and that is how we should look at DOF. The higher the magnification of our subject, the shallower the DOF. It’s as simple as that instead of thinking about two things, (Focal Length and Distance to Subject) we just think about one.

When we know that, we also know that the only true way to change the DOF (keeping the same magnification) is by changing our Aperture. The wider the aperture (lower number) the shallower the DOF. The tighter the aperture (higher number) the deeper the DOF.

All things being equal, a Headshot will have a shallower DOF than 1/2 Body than a full body. Use THAT to determine your aperture for the effect you want. i.e shoot wider open on a Full Body shot than a Headshot because a Full body shot is less magnified thus has a deeper DOF to begin with

Hope that helps


Depth of Field – In Depth

Depth of Field – In Depth

Everything you wanted to know about Depth of Field and some things you didn’t but you will be glad you did

So you may think you understand Depth of Field (DOF) but do you? Let’s try to confirm what you do know and maybe show you a couple things you didn’t.

What is Depth of Field?

Let’s start with a definition: Depth of field is the total distance that is in “acceptable focus” from our actual point of focus. Let’s clarify that definition further because we artistic minded hate reading definitions.

When you focus on an object, you have a “point of focus” that is the only part that is 100% sharp and in focus, then you have a “field of acceptable focus” in front of and behind that point. That area is the total Depth of Field Continue reading »

Help! I’ve broken my Bokeh and I can’t get up!

Bokeh is a term used for the Quality of the  OOFF (Out Of Focus Field) in an image. NO IT IS NOT the term for an image with a shallow depth of field. That would be: An image with a shallow depth of field. LOL

But a great bokah in an image is a very desirable things. Most times when we shoot HDRs we really don’t worry about this because we are shooting for a very deep DOF. Bokeh would be irrelevant for most of our shoots.

But suppose we want to be different, we want to use our artistic side and we want to shoot a subject and then have a very shallow DOF. No problem shoot away BUT as nice as HDR will make the subject of your image it will have a totally detrimental effect to the OOFF area and destroy any great bokeh your lens may have.

Let me show you, For this image I used my Canon 70-200L 4.0 lens which is known for it’s excellent bokeh. I shot a day lillie in front of my home with 3 exposures and at 200mm f/7.1. Now you may say f/71. That’s not going to give you a very shallow DOF, actually it’s probably still not enough since my Focal Length was 200mm and my distance to subject was 5 feet, that still gives me just a few inches of DOF. Shooting wide open would have given me less than an inch of DOF.

I processed the images in Photomatix Pro 4.1 and used the Painterly preset, Just taking the strength down a notch and adding a bit to the black levels.

Here is that image



















Now some may say,” That looks great”. And to an untrained eye it may. Because HDR brings out detail and perceived sharpness it is applying that to the background to the same degree that it does out subject where we do want the fine detail visible. The same thing can occur when someone oversharpens a standard photograph and applies that sharpening equally to the background. You are sharpening something that is not meant to be sharp and it destroys the look of the image.

But now look at the OOFF of a standard image with the true Bokeh of that area.


















Look at the softness and smooth transition of tone in the background. But we loose the extra tone and detail we may want in the our subject; the flower itself.

So is all lost? Not at all. Through the magic of Photoshop and our friend the layer mask, I took the HDR image and dragged it on top of my standard image and then just masked off the background to reveal the standard image background. Problem solved.

QUICK HINT: If you are dragging an image on top of another image and want to make sure that the two images are aligned. First start by dragging the image with the shift key held down. Then to fine tune the alignment, change the Layer mode on the top layer to “Difference” and the image should turn black, The better you align the images the more black the entire image will look especially on edges. Once you have the images aligned, return to Layer mode to normal.

This is the final image, HDR Subject, standard background with that creamy Bokeh