Heliopan 67mm Medium Yellow Filter (706703) Heliopans premier 67mm Medium Yellow Glass Filter is primarily used to bump up contrast and tonality on black and white films. The standard strength of the 3 contrast filters Heliopan offers; the Medium Yellow Filter slightly darkens skies, helps cut through haze, and increases overall contrast. It is the most common contrast filter used for black and white photography, producing an accurate tonal range and compensating for blue sensitivity of panchromatic film. Constructed from the highest German Schott Optics, which guarantees incredible optical resolution. Our glass is specially ground and polished to minimize internal reflections, while ensuring that the quality of your images are not degraded by using our optics in front of your lens. It is also specially hardened to resist most impacts. Our standard 8-Layer Multi-Coating minimizes reflections and does not interfere with the resolution of your camera optics. Our precision cut brass ring ensures a secure and sturdy fit, are more resistant to side impacts, and less likely to bind or cross-thread after extended use. We do not source any materials outside of Germany in the assembly and construction of our products. All raw materials are prepared and hand-assembled in our factory and do not leave our facility until they are completely inspected by our quality technicians.