Depth of field and Obliqueness

DEPTH OF FIELD

and Obliqueness

As I’ve discussed before, depth of field is a moving target. By that I mean the amount of DOF you get depends on a combination of factors that are constantly changing. These factors are:

1. Lens aperture 2. Distance from the camera to the subject 3. Distance from the subject to the background 4. Focal length of the lens

There is actually a fifth factor, although it is related to the ‘Distance from the camera to the subject,’ and that is the obliqueness of the digital sensor plane to the subject. We used to call this the film plane.

Look at the diagram on the previous page. The green line represents the plane of the digital sensor. The black line at the bottom represents the subject -- such as the butterfly in the photo. When the camera is angled to compose and shoot, the distances from various parts of the sensor to the subject plane aren’t equal. The top of the sensor is farther than the bottom portion of the sensor as shown by the red lines. Since focus is a function of camera-tosubject distance, the fact that the camera, and therefore the plane of the sensor, is oblique to the subject directly impacts depth of field.

This is very noticeable with macro subjects. With the photo of the butterfly on page 12, I had to use f/16 in order to have enough depth of field to make sure both the head and the trailing edge of the hind wings were sharp. If you look closely, though, it turns out f/16 wasn’t enough because I used a 100-400mm telephoto lens to take the picture.

The cameleon, above, also shows focus fall-off.

PANTANAL PHOTO TOUR

October 30 to Nov. 7, 2021

Jaguars in the wild Exotic birds in flight Caiman Giant river otters

The camera and macro lens were again oblique to the reptile.

On page 13, the ancient atrium of a home in Herculaneum, Italy (one of the towns destroyed in 79 A.D. with the eruption of Mt. Vesuvius that also razed Pompeii) shows the camera was oblique to the plane of the tiled floor. Everything here is sharp even though my lens aperture was f/4.5. Why? Because the focal length of the lens that captured this image was 24mm.

When the camera is oblique to the subject and you believe there will be a compromise in depth of field, here are the solutions for recovering lost depth of field.

1. Angle the camera so the back of it is as parallel as possible to the subject. This may require leaning over the subject, like an insect, so you are shooting down on it as opposed to photographing from a severely oblique angle.

2. Close the aperture down if possible.

3. Use a wider angle lens, if possible, because this increases depth of field.

4. Move further away from the subject. Even a few inches will make a difference if you are doing macro photography.

When photographing landscapes and the camera is directed downward so it’s oblique to the ground, oliqueness is still relevant. This is especially true if the foreground is positioned very close to the camera as in the shot above of a formal garden in Etretat, France. Even though I used a 24mm wide angle lens, I had to use f/16 to insure the leaves in the immediate foreground were as sharp as the distant ocean cliffs. Since I was handholding the camera this necessitated raising the ISO to 1250.

Had I moved back, say 10 feet, and refocused on the garden, I could have used a larger lens aperture and therefore a lower ISO. But that would have changed the composition, and this is the shot I wanted.

Pay attention to the oblique angle of your camera and you’ll be able to control DOF more. §

UPCOMING PHOTO WORKSHOPS

Carnival in Venice workshop

Photograph outrageous costumes in a medieval environment! Incredible colors, design, and creativity in one of the most beautiful cities in the world. Learn how to use off-camera flash, photograph models in sumptuous interiors, produce great images at night, and all the while enjoying Italian cuisine. This is a workshop not to be missed.

February 18-25, 2022

Frogs & Reptiles Workshop

This is a macro workshop to photograph beautiful, colorful, and intriguing frogs and exotic reptiles. Learn how to use flash with closeup work, how to use extension tubes, and how to take perfect exposures. Held indoors in a hotel conference room in St. Louis.

June 12 - 13, 2021

Winter Wildlife Workshop

Stunning pictures of North American animals including wolves, red foxes, arctic foxes, mountain lion, Canada lynx, and more. The animals will be in their winter coats and very beautiful. This is based in Kalispell, Montana.

February 2 - 5, 2022

W i n t e r W i l d l i f e Workshop

February 2 - 5, 2022

Based in Kalispell, Montana