The SW150 Mark II Holder fits via a SW150 Lens Adaptor that has been specifically designed for that particular ultra-wideangle lens (the adaptor is purchased separately from the filter holder).
This adaptor allows the SW150 Filter Holder to attach to the Sigma 12 - 24mm f4.5 / 5.6 lens*.
The adaptor consists of a front ring, a compression ring and a locking ring. When fitted, these form a collar that remains on the lens at all times.
*Please note that due to the physical size of this lens, and the extremely wide angle of view, the SW150 filter holder will vignette at the widest angles. To avoid this, we recommend using a minimum focal length of 15mm when using the filter holder with two filter slots and 13.5mm when using the holder with one filter slot.