Reverse Depth of Field
SetMyCamera’s recent update includes Reverse Depth of Field calculations. What is Reverse Depth of Field (RDoF) and why do I need it?
Traditional depth of field calculations are good for most cases but let’s explore special use cases. Here are some examples for which reverse depth of field can be easier.
What if we have a group of persons to photograph and we know the nearest person is 10 feet from the camera lens, and the farthest person is 20 feet away. If we have a 50mm lens attached to our Nikon Z6 camera, what is the best aperture (F/Stop) setting to just get everyone in focus? And at what distance should we focus to achieve the best result?
This example is a great application for SetMyCamera’s RDoF. From the figure RDoF1, we can see how to configure SetMyCamera to answer our question. We selected the Calculate F/Stop button option, entered our information, and the answer is F/6.96. But we don’t have an F/6.96 option on our camera.
Remember we are looking for the optimal setting? The F/6.96 value is between F/6.3 and F/7.1 that the camera can accommodate which are also displayed. Similarly, we have the optimal distance from the camera lens to the focus point to be 13 ft 4 inches.
Capturing the group of people successfully with the depth of field including the persons in focus requires we focus at a distance of 13 ft 4 inches from the camera lens. Most likely we don’t know of an object at 13 ft 4 inches. This suggests we have to find something at the preferred distance to focus on to be successful. Fortunately, we have choices. One is to expand the depth of field and focus at a point close to the optimal setting. Or we can find a subject at the 13 ft 4 inches marker and focus on it.
The previous example relies on a fixed lens. What if we have a zoom lens or other lenses available, and we desire a fixed aperture? SetMyCamera RDoF can find the best lens focal length too!
Modifying the previous example, let us consider a low light or simply a desire for a faster F/Stop value. If we have a zoom lens, what lens focal length is best?
In this example we refer to figure RDoF2 which highlights that we have selected the Calculate Lens button option. If we select an F/Stop of F/4.0, with the same 10 foot near focus and 20 foot far focus options, we find an optimal lens value of about 38mm. If this falls within our zoom lens’ capability, we have a solution. Notice that the optimal focal distance is now 13 feet 3 inches which is slightly different than the first example.
From the examples above, we learn that reverse depth of field can be an easier path to finding the optimal camera settings. The RDoF information can be transferred to the depth of field page for experimenting with alternatives if desired. The two methods are very compatible. One method or the other may show us alternatives that we may not have seen otherwise for our perfect photo.
More importantly, reverse depth of field offers a solution based upon the lens and F/Stop preferred solutions rather than the traditional approach of basing the solution upon entirely upon the distance, lens and F/Stop approach. Both are valid but sometimes we desire to find alternatives base upon our artistic intent which may require flexibility in alternative settings. Reverse depth of field offers a different perspective for our consideration.
