For manual focus lenses and most autofocus SLR lenses, the focusing ring and the focusing lens group are mechanically linked. How much the focus ring turns, and how much the lens group moves, this is the linear response.
Almost all autofocus micro lenses and a few autofocus SLR lenses (using stepper motors or linear ultrasonic motors) use electronically controlled focus rings. The most important feature is the absence of closest focus and infinity limits, and the inability to change the lens focus position in the event of a power failure. There is no mechanical linkage between the electronic focusing ring and the lens unit. Rotating the focusing ring sends a command, and the focusing motor drives the lens movement according to the command.
The electronic focus ring not only simplifies lens design but also contributes to miniaturization and lightweight. It also allows for greater flexibility in the way the focus ring can be used. For example, you can set the direction of rotation and linkage according to your own operating habits – for example, non-linear focusing is based on the speed of rotation to control the focus movement, slow rotation small movement, fast rotation large movement.
Here we also share with you the differences between different brands in terms of focus ring control.
Panasonic Micro SLR (GH6 for example) with compatible lenses can set non-linear or linear focus in the menu “Focus Ring Control” option. When choosing a linear focus, you can also customize the focus travel (from 90° to over 1080°).
- The focus travel is the angle of rotation required to go from closest to farthest focus. A smaller focus travel allows for faster focus movement; a larger focus travel allows for more precise focus adjustment.
Both Canon EOS R series (EOS R7 for example) and Fujifilm Micro Single (X-S10 for example) can customize the direction of focus ring rotation and linkage. The Canon feature is called “RF Lens MF Focus Ring Sensitivity” and it is easy to see that it is only available for RF lenses (not for EF lenses).
There is no focus ring control option on the Sony body, and whether or not the focus is linear depends on the lens. For example, Sony’s original lenses with “Linear Response Manual Focus” (LR MF) are definitely linearly focused.