Bokeh Solver
In essence, this calculator is fed some known quantities and it calculates unknown ones1. The quantities being physical properties of the scene you are shooting, the camera you are using or the image you are about to capture.
Please do check the tutorial below. Note that the calculator is not yet optimized for small screens or use of Imperial units. Enjoy!
Tutorial
Let’s take a look at the default configuration, assume for a moment that:
- You’d like to know how much out of focus blur you can achieve in your backdrop2.
- You know how big a subject you want to fit in the frame.
- The distance between your subject and the background is flexible, within reason.
This translates to the following settings:
- A fixed Subject size (a check mark in the Fix column and adjust value as desired)
- The known variable Subject to background distance on the X-axis (a check mark in the X-axis column and adjust range as desired)
- The unknown variable Relative blur on the Y-axis (a check mark in the Y-axis column). That will be the diameter across which background details are blurred as a percentage of the image size.
Now to add some needed camera parameters:
- Fix the Image size (that is, the sensor or film size the image is projected on).
- To compare multiple lenses, add their parameters Focal length and Aperture F-stop to the configurations list (check marks in the Config column)
- Then specify each configuration’s individual parameters in the Configurations list.
- You can add or remove configurations using the + and - buttons, and adjust the line colors.
If all goes well, now you have a plot under Results, comparing what out of focus background blur you can achieve with each lens for a given distance.
Advanced use
Now for the fun part, if that doesn’t quite describe your situation you can mix things up. Any parameter can be used as an X- or Y-axis, locked or used in a configuration. See below a description of the parameters. There are many useful configurations to explore, some ideas:
- Calculate what shot you can take in a limited space with a backdrop of a given size.
- Calculate the depth of field of a setup (the “background” can be placed in front of the subject to calculate the front limit)
- Calculate the hyperfocal distance for a lens
A word of warning, there are just as many (or possibly many more) combinations that don’t yield any meaningful results. If too few parameters are specified, the system is under-defined and the parameters that could not be calculated will be shown in blue. Conversely, if too many parameters are specified this results in conflicting derivations of some of them, the system is over-defined and the conflicting parameters will be shown in red.
It is possible that you have a configuration that is both over- and under-defined at the same time, or various other edge cases in which either the error indicators don’t show up, or they don’t make sense. In general, the solver is more robust than the error checker, and the best indicator for an available solution is the plot showing up ;)
Parameters
Lastly, here is a somewhat more detailed explanation of the parameters.
- Subject distance — The distance between the camera and the plane in which the in-focus subject is located.
- Background distance — The distance between the camera and the plane in which the background is to be located for a correct out of focus blur indication.
- Subject to background distance — The difference between the subject distance and the background distance. A negative distance indicates a “background” in front of the subject, this is perfectly valid. It is used to calculate the level of blur of an object in front of your focus plane. Note, however, that the blur indication will then have a negative value.
- Subject size — The size of the area located in the subject plane that will be projected onto the image. In other words, the size of the subject if it were to fill the frame edge to edge.
- Background size — The size of the area located in the background plane that will be projected onto the image. If you have a backdrop of a specific size that you would like to have in view then that’s the background size.
- Subject to background ratio — The ratio between the subject size and the background size, and an indication of how compressed the background will be.
- Image size — The size of the camera sensor or film. Dependent on whether the horizontal or vertical direction of the composition is relevant and whether it is a portrait or landscape shot, the relevant image dimension should be chosen.
- Focal length — The focal length of the lens (at last an understandable definition).
- Field of view — The angle of the cone that will be projected onto the image.
- Aperture diameter — The absolute diameter of the lens aperture.
- Aperture F-stop — The diameter of the lens aperture relative to the focal length.
- Background blur diameter — The distance across which objects in the background will overlap on the projected image due to out of focus blur. This is an absolute distance measured in the background plane.
- Relative image blur — The distance across which objects in the background will overlap on the projected image due to out of focus blur, expressed as a percentage of the image size.
