Comment by alexbock

I enjoy monochrome infrared photography at wavelengths longer than 1000 nm using a Sigma sd Quattro (no Bayer filter and the sensor IR filter is reversibly user-removable). To reduce exposure times as much as possible, I've been testing an AR-coated near infrared achromatic doublet (AC254-050-B-ML) with a 3D-printed housing to attach it to the camera mount with a manual focusing barrel. The next step is to design a fast double gauss lens that can similarly be assembled from readily available NIR-coated stock lens elements.