carried out some exposure steps for Kamra #3 Bulb. Although the bulb has a focal length of around 100mm, the aperture opening is Ø25mm or /f4.0. 3 test print exposures were done. Rated with light meter at eye level, f2.0, 2.8, 4.0 the most accurate and ideal is between /f2.0-2.8 the bulb does collect alot of light and causes alot of flares and adds diffusion / soft focus