The 74-ACH Adjustable Collimating Lens Holder is a versatile assembly for mounting lenses at multiple positions vertically and horizontally and is especially useful for transmission measurements of samples up to 10 cm thickness. Its anodized aluminum base and adjustable mount bars accommodate collimating lenses using four 3/8-24 threaded holes, spaced 1″ apart starting 1″ from the top of the bar.