The 1.25x is one of the most classic squeeze factors used by popular anamorphic lenses like Panavision.

In adition to creating a 25% increase in the horizontal field of view, the 1.25x squeeze has two other advantages:

1.
2x Constant Squeeze
Screw the Sirui 1.25x adapter on to the Sirui 1.6x anamorphic lens to achieve a 2x squeeze.
With a higher squeeze comes more noticeable anamorphic characteristics. For example, the thinner bokeh and shallower depth of field.
The 2x squeeze allows more information to be included into the frame, giving you more flexibility to reframe in post.
Compared to traditional 2x anamorphic lenses, this combination is reasonably compact and affordable, offering the best value for the money.

2.
Approx. 16:9 Common Aspect Ratio
Most professional digital cameras, such as ARRI, use 4:3 sensors. When a 1.25 anamorphic adapter is used on these cameras, the image can be directly desqueezed to an approx. 16:9 aspect ratio, which is an universal format for modern commercials, TVCs etc.

Using the 1.25x adapter on spherical lenses and shooting 16.9 will result in a 20:9 aspect ratio, which allows you to play videos in full screen on smartphones.

Wide compability
The Sirui 1.25x adapter has an 82mm rear thread. Three step-down rings (67, 72, 77mm) an a step-up ring (92mm) are available to match a wide array of popular lenses on the market.

Compact & Portable
With a length of only 46.5mm and a weight of 650g, the adapter is relatively small and lightweight.

Front single Focus
Set the base lens at infinity, and use only the adapter to focus.

Constant Squeeze Ratio
The adapter maintains a constant 1.25x squeeze ratio at all focusing points, eliminating the "anamorphic mumps" effect on your talent.