The NIRI collimator lens is a two element lens made of LiF and BaF2. The first lens are both spherical with the first being a meniscus while the second is plano-convex. They both have a diameter of ~55mm. It is located between the two filter wheels on the science path optical table. Below are two photos of the collimator unit without the filters wheels mounted on the table.

Below is a photo of the science path optical table showing the collimator lens, two filter wheels and pupil mask/filter wheel all mounted.