The Key to Tack-Sharp Photography

The Key to Tack-Sharp Photography

Fact: Depth of field will remain constant across all formats and focal lengths as long as the aperture and the image size remain the same. There are several factors that determine how sharp, or not sharp, an image may be. One of those is depth of field, and another is the movement of the subject matter that occurs while the shutter is open. Here, I will discuss depth of field.

One of the most frustrating things that has happened to me in the creation of photographs is making a photograph I think will be stunning, sending the film out for processing (color film only for me), or processing a black-and-white negative, looking at the film on the light table where it has great tonality and a very pleasing and dramatic composition—everything I wanted—and then, on closer inspection, seeing that I didn't have enough acceptable depth of field to render a sharp photograph throughout the scene. To gain a clear understanding of acceptable depth of field, let's first define it.

Acceptable depth of field is the amount of space in front of and behind the plane of critical focus that appears to be acceptably sharp. The plane of critical focus is the place where the lens is focused, and nothing in that image can be sharper than the object(s) at the plane of critical focus. As the distance of material from the plane of critical focus increases—either toward the camera or toward infinity—objects will be less and less sharp until they are so unsharp that their lack of sharpness can be seen by the viewer of the photograph. What is acceptably sharp in one photograph may not be acceptable for another.

Depth of Field

As an object diverges from the plane of critical focus, either in front of or behind it, it will become more and more blurry, or out of focus, until it is unacceptably sharp.

If the camera and lens are focused at exactly 8 ft, as in the drawing, an object included at 7 ft or 9 ft will be more out of focus than what is at 8 ft. These objects may appear to be sharp and may be acceptably sharp, but they aren't critically sharp. That is a critical thing to understand.

"An old Aspen, Routt National Forest." I was in this Aspen Forest and came on this very old Aspen. I used a slight mist that had formed and limited depth of field to isolate the main tree and rendered it very light, high key.

We were staying in Northern Colorado, almost in Wyoming. I lost myself in the wonder of this aspen forest. An aspen grove, by the way, is one of the largest living organisms in the world since all the trees in a grove can originate from a sucker put out by one tree. They may all be the same tree... that is a marvel. In my wandering, I came to this tree and was struck by how old it must be. There was a slight mist forming, as often happens in colder weather at altitude, which helped to separate the main subject of this image from the background trees. I call that "atmospheric depth of field." Then, using a large aperture, I employed "photographic depth of field" to throw the trees in the background slightly out of focus. The point of this discussion is that you can and should use depth of field as a compositional element.

"Sunstruck Cottonwood, Cerillos, New Mexico." I used a Toyo 45A camera, 90mm Sinaron lens, no filter and Kodak T-Max 100 film set at ASA 50.  Obviously, in this photograph, everything had to be as sharp as it could be made to be.
This photograph, "Sunstruck Cottonwoods, Cerrillos, New Mexico," obviously had to be done at the other end of the depth-of-field discussion. I wanted all the sharpness I could get—from the grass nearest the camera to the trees in the distance. So, I wanted all the depth of field I could achieve. However, with the obvious issue that arises in photographs of this kind, I also had to take the occasional breeze into account. It presented numerous problems that had to be solved, and sometimes, like a riverboat gambler, you just have to take the photograph and hope there is no breeze while the shutter is open.

Managing Depth of Field

Depth of field is managed using two factors: image size on the viewing screen and aperture size. As the aperture number increases, from f/5.6 to f/32, depth of field also increases. Conversely, as the aperture number gets smaller, depth of field also gets smaller. Said another way, as the size of the aperture gets larger—going from f/32 to f/5.6—depth of field decreases, and vice versa. We can control what is acceptably sharp to a great degree by the size of the opening in the lens that allows light to pass through the lens, through the shutter, and to the media, whether the media is electronic or film. The laws of physics governing this phenomenon do not change between film and electronic means. (This should be obvious, but I have had people argue vociferously that the optics governing film and electronic media are different. I want to lay that one to rest: the laws of optics remain the same across media types and media sizes.)

The size of the image at the focal plane is another factor in controlling depth of field. Some people will say that three things control depth of field: the f-stop being used, the camera-to-subject distance, and the focal length of the lens being used. That statement is true, but only partly so. First, the f-stop being used is always a factor in determining your working depth of field—always. The second factor is the image size at the focal plane. Because of perspective, objects become smaller as they recede from the focal plane and larger as they approach the camera. Next, the focal length of the lens being used causes the object to become larger or smaller, depending on the focal length. A wide angle lens, like a 17 mm or 15 mm lens, will reproduce a certain image size at a given distance, while a 300 mm lens from the same spot will produce a larger image at the focal plane. The reason this is important is that the depth of field with a certain lens, at a certain distance, and at a common f-stop will remain the same whether you are using a crop frame or full frame digital camera, a medium format camera, or, as I do, a large format camera. The commonality is that depth of field will remain constant across all formats and focal lengths as long as the aperture and the image size remain the same.

If you photograph an object at a distance of exactly 11 ft using a full frame digital or film camera or an 11x14 large format camera with a 300 mm lens set at f/22, the image size and depth of field for both cameras will be exactly the same. While the focal length of the lens and the distance from the camera to the subject influence depth of field, acceptable depth of field only changes as the two are used in combination. The primary method of controlling depth of field is by changing the size of the aperture in the lens.

"Bisti Overlook, New Mexico." A time when having very great depth of field is essential. It was absolutely essential to hold depth of field throughout the photograph. Toyo 45A camera, 90mm Sinaron lens with a #61 Dark Green filter, Kodak T-Max 100 film.

There is actually another factor in determining depth of field that is not often discussed but is a primary benefit of using large format cameras or a tilt-and-shift lens on a 35 mm-based camera. That is the "Scheimpflug Principle," and I will address that in a future article. Briefly, the Scheimpflug Principle allows the photographer to shift the plane of critical focus from running horizontally to vertically. That makes depth of field run in a vertical direction, making it possible to have everything in front of the camera in critical focus, from just in front of the camera to infinity.

Nathan McCreery's picture

Nathan McCreery is a commercial & fine art photographer living in New Mexico. He works easily in the studio and on location, usually using large format film cameras and processing and printing his own film in a traditional wet darkroom. He creates exquisite photographs of the American West, and a few other places.

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25 Comments

I appreciate your description. With film photography planning is an important part of the process. You can't just play with a variety of settings, shoot multiple images, and look at the monitor of the camera to see what you like best. Choosing to use film separates the photographer from the image taker, it is a much more difficult process in every way. I started my photographic journey in the 1980's using film. My successes were very limited and when digital came along, I adopted it right away. It is so much easier. I respect and admire your choice to stay with a much more difficult process and your obvious success is illustrated through your images.

Thank you. If I were designing an art school or university photography program every student would be required to take at least two semesters of photography using either a large or medium format camera. They teach not only the fundamentals but also economy of movement and effort. Having worked in film for so many years, in the event that digital is called for I revert to my film training and work habits more from habit and instinct. At some point in the not too distant future I intend to address the issue of composition, and building a composition. I try to do everything with a purpose in the field, as well as the studio. While it's true that it costs me nothing to make 500 images of the same thing - an exaggeration I think - it does cost time at the computer to edit those images. So while the dollar cost is much less, the economy of time is very different.

I did take a photography class, not a program, in my university training (1975). It was 10 weeks long and maybe 2 days a week. I still have the Rolleicord camera I used for the class although I haven't used it since. The class focused mostly on the mechanics of photography, how to use the camera and then the darkroom processes. I can't recall any emphasis on the artistic aspect of photography, the closest thing to it was focus. Depth of field was discussed briefly simply as a component of controlling focus. I do remember how difficult it was to get one good photograph from a 24 exposure roll of film. So much easier these days to get a good one. The ability to recognize "good" is still up for debate and should get more attention than it does. I'll be looking for your next article, thanks!

Jon Reed, the reason I would insist on each person taking at least two semesters using film cameras only, and using them in manual mode only, is that it would force people to learn fundamentals. My concern with modern photographers is that the fundamental skills needed aren't being taught, and they will be lost.

I don’t follow what you mean about the scheimpflug principle shifting the plane of critical focus from horizontal to vertical. Is that a typo? Your diagram shows that plane running vertically up and down.
I assume the trick there is cocking the lens in relation to the film plane, but you ended the article kind of abruptly.

Yes, it is incomplete. I try to limit writings here to about 1500 words, so the Scheimpflug Principle will have to take another posing. But yes, using that principle we do shift the plane of critical focus to a vertical rather than horizontal plane. The diagram only shows depth of field when using a camera without tilt capabilities, like almost any camera based on a 35mm type, or medium format type of camera chassis.

wonderful article thank you. I am looking forward to the next article on the Scheimpflug Principle.

Diffraction causes a loss of acuity and this is more noticeable with a digital sensor than for film. So for my full-frame sensor - if I shoot over about f/8 it can become noticeable. This means I pretty much never use f/22... and probably f/11 is about as small an aperture as I would risk.

Diffraction is a problem, less now than it used to be. Remember though that I am using large cameras with apertures that run to at least f-45, most to f-64 and one goes to f-90. All of these lenses have what I call a sweet spot where the lenses resolution is maximized, and when possible I try to use that aperture. Most of the lenses I use will have a "sweet spot" at around f-22 or 32, and beyond that image sharpness begins to decline, although the decline is more theoretical than practical.

My favorite technique for choosing depth of field is just experience with specific camera/lens/aperture combinations, alongside experimentation with other techniques if time and opportunity allows: focus stacking, post processing. I used to just use a magnifier on the ground glass while stopping down, but I wonder if my eyes could do that now! Electronic viewfinders allow some of the same function, but experience is much faster in the heat of the moment.

In the past George Douvos had several essays on depth of field that were the best I've ever seen. His apps are still on the App Store as of this writing: Optimum CS-Pro, Focus Stacker, TrueDOF-Pro, but his website domain is gone. I guess I should have downloaded the essays and left good reviews when I could! (PS I did, I found one of his essays in my archives. I hope I can find a working url to share.) His calculators allow you to choose the amount of blur you consider acceptable for any combination of sensor, lens, aperture, even film resolution. PhotoPills website has an advanced DOF calculator, but is limited to equipment listed in drop-down menus.

There are several hyperfocus calculators on the internet. I have one in my pack, however the most effective thing I have found is to find what I think is about 1/3 the total distance in the photograph, front to back and focus there. Then using a loupe stop the aperture down until the object the furthest away comes into apparent focus, then stop down one more stop. Usually that comes out to about f-45 on my large cameras. Fixed focal length lenses have depth of field scales on them, which are very useful.

Yep. It just takes time to find out how that translates to other formats. So much depends on how the image is output, how big a print, how big and how much resolution the screen, and the viewing distance. Once you get to the limit of what is visible in the viewing conditions, there just is no more needed. I grew up learning photography through photo book, mostly half-tone reproductions, so I imagined more than the reality of the photograph. When I finally got to see real prints by my photographic gods, I was sometimes relieved to find they were just photographs. Sometime, though the print was transcendent. Often, but not always, they were contact prints. My favorite comment on the topic recently was attributed to Henri Cartier-Bresson, "Sharpness is a bourgeois concept!", but I don't think he cared much for the print quality anyway.

"In the past George Douvos had several essays on depth of field that were the best I've ever seen. His apps are still on the App Store as of this writing: Optimum CS-Pro, Focus Stacker, TrueDOF-Pro, but his website domain is gone."

You may be able to find most of this on archive.org

Yes, and I was able to download the essays. The website seems to have been taken down during COVID, so I hope he survived.

I'm so happy to see an article that states the fact that DOF is based on focal length, focus distance, and aperture. Format/negative size does not affect DOF. A 50mm lens is a 50mm lens. DOF with that lens does not matter if it is on Micro 4/3 or 11x14 film. With all things the same, the DOF is the same. The image on the film/sensor will look different because of angle of view. But, the perceived DOF and out of focus area will be the same.

I have argued with people about this before, including a well known half of a famous YouTube duo about this. They kept saying that 'equivalent' focal length between formats and lenses meant the DOF was the same. The worst part is that they are giving poor info to millions of viewers.

Worst source of info period is on YouTube.

Thank-you.

By image size do you mean "field of view"? FOV

No, Field of view is how much real estate the lens covers left to right and in a vertical direction, and as you know that can vary with the focal length of the lens being used, and with the format of the media behind the lens, at the focal plane. For instance, I can use a 47mmXL lens on my 4x5 camera. It will have a field of view approximately the same as a 15mm lens on a full frame digital camera - super wide angle. So field of view will vary for a focal length of lens depending on what size the media is at the focal plane. It is more complicated than that if we talk in strictly technical terms, but that should be sufficient for this answer. On the other hand, if the focal length of the lens and the distance of the subject to the camera are constant, then the image size of the subject will also be constant and, as a consequence, the depth of field will also be the same, provided that the aperture size is also constant.

In other words, if I am using a 100mm lens at f-16 at a distance of 10 ft. with a 4/3 digital camera, a full frame digital camera, a full frame 35mm camera, a medium format film camera like a Hasselblad, or a 4x5, 5x7 or 8x10 view camera, the image size of a 6ft human figure will remain constant and so the depth of field will also remain constant. If something is changed in that equation, such as aperture size or camera to subject distance, then the depth of field will also change. As long as the focal length of the lens being used, image size at the focal plane - due to perspective -, and aperture being used remain the same, depth of field will also remain the same.

Great discussion thanks.

Great article! Depth of field is such a powerful tool for shaping an image, and your explanation makes it so approachable. The examples of isolating the aspen tree versus achieving full sharpness in the cottonwoods are fantastic demonstrations of how creative and technical choices work together. I’m excited to read more about the Scheimpflug Principle in your future article—tilt-shift techniques are fascinating! Thanks for sharing these insights!

Paul Tocatlian
Kisau Photography
www.kisau.com

Thank. Scheimpflug is difficult to explain in an article, very easy to demonstrate live. I am working on the article now.

Looking forward to it!

I submitted the writing to F-Stoppers yesterday. Scheduled for Feb 19 after 5:00PM EST.

Looking forward to it!