About Locus...

The center of Locus is its main window where most of the information is displayed. It is divided into three sections as shown at right:

• camera section
• lens section
• scene section

Plus, there is a vertical display area along the right.
 

Camera
The "Camera" section gathers the parameters for the camera and the first step in using Locus is usually to select or enter the camera information. This is very easy because Locus includes a database with the parameters for many hundreds of cameras. All you have to do is select your camera from the "Camera" list. Or you can manually enter the parameters if your camera is not in the database. By the way, the database is fully editable and we offer free database updates which you can download from this website. Here are the camera parameters that are used by Locus:

• Format Size - The width and height of the image area of the image sensor (digital cameras) or film frame (film cameras).

 
• Format Resolution - The width and height in pixels of the images produced by the camera using the native resolution of the image sensor (digital cameras). Film cameras don't have "pixels" so this is an equivalent film resolution for them.
   
• Circle of Confusion (COC) - The maximum size of an in-focus point on the focal plane inside the camera (on the image sensor or film frame). Locus provides a very sophisticated ways to handle the COC: It can be automatically calculated for your camera by scaling a reference value and it can account for both the Output Size or Enlargement Factor and the output Viewing Distance.

 
• Field of View Factor (FOV Factor) - Determines the equivalent Focal Length for a lens on a 35mm film camera that would have the same FOV as a lens on the selected camera.
   
• Minimum Shutter Speed - Locus recommends the slowest usable shutter speed if you want to overcome two different causes of blurred photos: camera shake and subject motion.

In addition to the above parameters, Locus also calculates the camera's Aspect Ratio, Megapixels and, once a lens Focal Length has been entered, its minimum recommended Shutter Speed for hand-held shooting without the aid of image stabilization.
 

Lens
The "Lens" section gathers the parameters for the lens and the second step in using Locus is usually to enter the lens information. Here are the lens parameters that are used by Locus:

• Optical Projection - This parameter tells Locus how to calculate the Angle of View of a lens. It is the method used by the lens to "map" the three-dimensional scene onto the two-dimensional image sensor or film frame.

 
• Focal Length - The distance between the optical center of the lens and the focal plane (image sensor or film frame) inside the camera.

 
• Teleconverter - Locus allows you to enter the magnification factor of a teleconverter so you can see how it will affect the image.

 
• Angle of View (AOV) - The portion of the scene within the view of the camera and lens. It is measured as an angle in degrees. Locus will calculate it for you or it can be entered manually.

 
• Lens Classification - The lens is assigned a common Lens Classification such as "wide", "normal" or "telephoto" based on its AOV with the selected camera.
   
• Diffraction Limit - Diffraction causes light to bend and scatter and the smaller the Aperture (the larger the f-stop), the greater the diffraction. The Diffraction Limit is the smallest Aperture (largest f-stop) that should be used if you want sharp in-focus pictures at full resolution. It is calculated automatically.
   
• Aperture (f-stop) - The opening in the lens through which light passes into the camera. It is expressed as an f-number. When a teleconverter is present, Locus offers the option to automatically adjust the Aperture.

 
• Aperture Diameter - A rough estimate of the diameter required for the selected Aperture and Focal Length. It is only an estimate because the complexities of lens design usually cause the actual diameter to be a bit smaller.

 
• Hyperfocal Distance - The Focus Distance to use if you want the Depth of Field to be infinite. When the lens is focused to the Hyperfocal Distance, everything in the scene should be in focus from one half the Hyperfocal Distance to infinity. With the help of sophisticated COC adjustments, Locus can calculate an accurate Hyperfocal Distance for modern cameras.
   
• Focus Distance - The distance between the focal plane inside the camera (the image sensor or film frame) to the place in the scene where the lens is focused (the point of maximum focus).

The lens parameters are a mixture of user-entered and Locus-calculated values. Locus makes it easy to identify one type verses another by the color of the text. Input boxes with white text require you to enter the value and input boxes with green text are locked since Locus will supply the value. To further help you, many labels include "balloon help". These are small text boxes that appear when you hover the mouse pointer over a label. They include descriptions of terms to help you understand the program. If desired, you can turn off this feature.
 

Scene
The "Scene" section gathers the parameters for the scene and the third step in using Locus is usually to analyze them. Most of them are calculated for you based on the camera and lens parameters. Here are the scene parameters used by Locus:

• Field of View (FOV) - The size of the portion of the scene within the view of the camera and lens at the Focus Distance.

 
• Scene Resolution - The area covered by one image pixel at the Focus Distance. It represents the smallest detail that can be resolved by the camera imager with the selected lens.

 
• Magnification - Shows the relationship between the size of a real-life object at the Focus Distance and the size of its image on the focal plane inside the camera.

 
• Total Depth of Field (DOF) - The depth of the in-focus portion of the scene. It is located between the Near Focus Limit and the Far Focus Limit.

 
• Near Focus Limit - The beginning of the DOF. It is the closest point to the camera where the scene will look in focus.
   
• Front Depth - The portion of the DOF that is in front of the Focus Distance.
   
• Far Focus Limit - The end of the DOF. It is the farthest point from the camera where the scene will look in focus (measured on-axis to the camera direction).
   
• Rear Depth - The portion of the DOF that is beyond the Focus Distance.
   
• Foreground Distance - A distance of your choice to a point in front of the DOF where you would like to calculate the Near Bokeh.
   
• Near Bokeh - The amount that the scene is blurred at the Foreground Distance.

 
• Background Distance - A distance of your choice to a point beyond the DOF where you would like to calculate the Far Bokeh.
   
• Far Bokeh - The amount that the scene is blurred at the Background Distance.
   
• Bokeh at Infinity - The amount that the far distant background is blurred.

Note: You may have seen the word "bokeh" before but not known what it means. It is a Japanese word meaning "fuzzy". It has become the industry-accepted name for the out-of-focus portion of a photograph. Locus calculates it as a percent of fuzziness or percent of blur and Locus uses the COC for a zero reference. In other words, when the blur is no greater than the COC, the blur is 0%. When it is twice as big as the COC, the blur is 100% and so on. This powerful feature helps you characterize the out-of-focus portion of your shots so you can decide beforehand if your foreground and/or background will be as diffuse as you want.
 

Display Area
The vertical area along the right side of the main window is reserved for displaying various drawings to help the user visualize the camera and lens.

• Camera Maker Logo - When a camera is selected, its company or product line logo is displayed at the top of the display area. These logos are the property of the respective camera manufacturers and are displayed here only to help Locus users quickly identify their cameras. Locus is not affiliated with any camera manufacturer.
   
• Lens Perspective - Shows the view of the scene through the lens. As used in Locus, it is dimensionless and is controlled only by the AOV. It's purpose is to help you quickly compare various lens Focal Lengths. It is represented with two drawings to show the rate that objects in the FOV shrink as they recede into the distance. The first drawing represents the Lens Perspective with rectangles and the second with people (head and shoulders).
  

Units
Locus offers an extremely wide range of distance units from the microscopic to the astronomic. Metric units go from attometers to terameters. English units go from inches to miles. Astronomic units go from AU to exaparsecs. You can configure Locus to automatically scale the units to fit the size of the values it calculates and you can exclude select units from its auto scaling. For example, if you don't want to use metric units smaller than a millimeter, you can turn off all the smaller ones.
 

Camera Database Editor
Locus includes a camera database with information for many popular cameras. You can add, remove or edit any camera in the database and Locus includes a comprehensive Camera Database Editor to assist with this (shown below). Many of the features of Locus rely on knowing the Format Size and Resolution of the camera. The Camera Database Editor can help you determine this information. It includes a pop-up menu with the Format Size of many popular image sensors and film frames and it can estimate the average equivalent Format Resolution for several categories of professional-grade film. Of course, you can manually enter any values you desire.

 

COC Calculator
The Circle of Confusion (COC) is at the heart of the equations that calculate when things appear in or out of focus. Yet most computer programs and Depth of Field (DOF) tables treat it as a static value. It is not. It changes with the Enlargement Factor of your photo output and it changes with the Viewing Distance to your photo. Locus provides a COC Calculator (shown below) to help you include these factors into the COC value for your camera. At last, the focus of a scene can be calculated accurately for modern cameras and photo media!

 

Crop Calculator
How tightly do you need to frame your shot? Locus provides a Crop Calculator (shown below) to help you answer the question. One way it does this is by calculating how many image pixels are needed for your output—the unneeded portion can be cropped. It can also help you determine how far away to locate your camera from your subject in order to frame it proportionally for your intended crop.

 

Focal Length Calculator
Locus provides a Focal Length Calculator (shown below) for rectilinear lenses to help you determine the Angle of View (AOV) and Focal Length needed to achieve a desired Field of View (FOV) at a specified Focus Distance.

 

Speed Calculator
How fast do you need to set your camera's shutter speed so you can "freeze" the motion of a moving subject? Locus provides the answer with its Speed Calculator (shown below). It uses the Direction of Travel, Speed and Distance to Subject to determine the answer. It considers not only the speed of the subject along its path, but also the change in size of an approaching or receding subject and the distance the subject can travel and stay within the Depth of Field (DOF). Plus, you can control the sensitivity of its calculation to produce faster or slower speeds.

Printing
The data in the main window, including the Lens Perspective drawing can be printed. In addition, Locus includes a sophisticated DOF table generator (shown below) so you can print DOF, Focus Limits and FOV tables for different Focus Distances.

 

Clipboard
Locus also provides several ways to export data and tables to third-party programs via the Windows clipboard. Everything that you can print can also be "copied" to the clipboard and "pasted" into a word processor, page layout or graphics program.
 

User Manual
Locus includes a detailed and well-illustrated User Manual in the form of a Windows Help document that is contextually linked to the program. What this means is that when you press the "F1" or "Help" key of your keyboard, the User Manual will open to a relevant topic whenever possible. Plus, the User Manual includes an "Illustrated Locus Dictionary" to describe the terminology of the program. Most of the illustrations on this webpage are from it. It also includes topics such as "Choosing a Lens", "How to get sharp in-focus pictures", and "How to get blurry out-of-focus backgrounds". Our customers have told us that the User Manual alone is worth the price of the program. It contains a wealth of information for beginners and advanced photographers.