Northern Cross High Precision Metal Focusing Mask, 85-118mm. I purchased this for astrophotography, but realized I made a mistake. Please note that this is for astronomical observation, not astrophotography. The following is an excerpt from the product page: High-precision metal construction. Compatible with outer diameters (e.g., hood outer diameter) of 85-118mm at the end of the telescope tube. This part allows for easy focusing with digital cameras and CCD cameras without being affected by seeing conditions.