One of the major benefits of mirrorless cameras is improved autofocus. 100% coverage and 5000 autofocus points. So, are all images you make will the 100% sharp 100% of the time? I’m afraid not. No matter how good autofocus gets, there will always be times when you take a portrait and can’t get both eyes to be sharp. Is the autofocus at fault? No, the photographer is.Advertisements I shoot with a DSLR, and I will be doing so for years to come. Sure, if autofocus sucked on my current equipment, I would upgrade. I don’t see improved autofocus as a valid reason to upgrade in most cases. That includes portraiture. The argument for autofocus goes something along the lines of sharp eyes and faces. What that argument doesn’t consider is how f/1.2 portraits become mainstream. There is a visual appeal to them as the background vanishes, but at the same time, the face does too. The fetish for sharp eyes in portraiture is becoming a major selling point for expensive cameras. It doesn’t even stay with just humans. Animal eye-tracking is another major benefit of mirrorless cameras. Here is my question, though: What about the rest of the body? The problem isn’t even in Eye-AF becoming a staple of photographers working with mirrorless as it is the limiting effect of it. A photographer who only worked with Eye-AF will probably not bother with issues like depth of field limits, hyperfocal settings, and so on. This results in a poor understanding of what sharpness is, and it leads to portraits where the only sharp thing is the eye.
Why Does It Matter?
I will use me as a first example. I never had to bother with understanding how field cameras work or working with silver plates. However, both interest me immensely because I see the creative possibilities they can open up to my fashion photography. But I digress… Now, for a real-world example: let’s say a client came to you and said that they need a macro portrait where everything from the tip of the nose to the neck is sharp—a common practice in commercial beauty photography. They hand you a 200mm f/2.8 and a 24-70 f/2.8. What do you do? Which subject-photographer distance do you take? Do you refuse the job? Is it even possible? The answer to the last question is yes: if you know precisely how focus works and what it is.
What Is Focus?
The question sounds as simple as the answer. Focusing is essentially adjusting your lens to resolve the maximum amount of detail with the highest contrast and sharpness. An out-of-focus image is not sharp and lacks clarity and contrast. They are considered to be unacceptably sharp. If an object is out of focus, it is beyond the depth of field. If an object is in focus, it is within the depth of field. Here are some key definitions I will be using:
Depth of field is the gap in which the subject will appear to be acceptably sharp. A shallow depth of field means that only a short gap exists. Since the depth of field is a gap, it has limits.Near limit(DoF) is known as the closest distance to the camera in which the object is sharp whileFar limit(DoF) is defined as the furthest distance from the camera and the acceptably sharp limit.Hyperfocal distance: if you want to keep everything at infinity tack sharp, the hyperfocal distance is the closest distance you can focus a lens at.Near limit is simply the distance from your camera to the first object that is sharp if you’re focusing on the hyperlocal distance. It is always half the hyperlocal distance.
Factors Affecting Depth of Field and Hyperfocal Distance
Focal length
Did you ever notice that at 14mm, objects are sharp even at f/2.8 while at 200mm, you need to stop down? That’s because at short focal lengths, the hyperfocal distance is very short, and the depth of field is quite large. With long lenses, the hyperfocal distance increases, but the depth of field decreases.
Sensor Dimensions
From day one, we’re told: a full-frame sensor makes better bokeh. That is because a larger sensor captures more of the scene at the same focal length. If you were to crop a full-frame image to 1.6 of its size, you would get what an APS-C camera would see. However, that is a relative change. On a medium format camera (large sensor), an 80mm lens sees the same as a 50mm on a full-frame camera. However, the medium format lens is still a longer focal length, meaning that the depth of field will be smaller.
Aperture Setting
As you close down the aperture, you increase your depth of field. f/2.8 is known to produce creamy bokeh, while f/8 makes less. However, at f/8, you are guaranteed that more of your subject will be acceptably sharp.
Subject dimensions
A subject bigger than the depth of field will appear out of focus.
Subject to Camera Distance
Remember hyperfocal distance? If your subject is beyond that distance, you can be sure that it will be acceptably sharp.
Case Studies
I don’t believe in learning without practice. The definitions above are useless if you don’t understand them. Here are real-life scenarios:
Beauty Photography
One of the most common mistakes I see with beauty photography is when the face loses focus somewhere around the ears. To combat this, we will need a depth of field that is larger than the dimensions of the face. For that, a shorter focal length closed down the aperture, and a bigger subject-to-camera distance will be helpful. When I am photographing beauty, I am either with a 70-200 f/2.8 at f/13-f/22 very far from the model, or if the situation doesn’t allow it, I use a 24-70 at 60-70mm at f/13-f/22 and crop in.
Fashion Photography
When in the studio, the whole subject must be sharp, while assignments on location vary. In any case, a focal length between 40-60mm and f/13 will do the job. Keeping the subject further than 3 meters(10 feet) helps too. I would suggest having a large depth of field since it allows the model to move freely around the set and try poses.
Closing Thoughts
Mirrorless autofocus is useless unless you know how to use it. Knowing how to use focus is crucial to being a more proficient photographer. As much as photography is an art, it is also a science in which proficiency is paramount. Relying on autofocus is sometimes not good enough if a client asks for a specific look. Deepening your knowledge in photography is much more of a long-term game than praising mirrorless for its Eye-AF. I’ll leave off with a thought: there are blurry eyes in In Annie Leibovitz Portraits 2004-2016 so as in Mark Seliger’s Photographs.
