Astro optics pvt. Ltd. An iso 9001 : 2000 certified company manufactures various types of optical components and lenses are one of them. Astro optics pvt. Ltd. Presents a range of filters which are used to `filter` out light, which means to separate out wavelengths. Being a part of that dichroic filters are coated filters which transmit one part of the spectrum and reflect another. For example they can transmit the visible and reflect the ir region [hot mirrors] or they can reflect the visible and transmit the ir [cold mirrors]. Dichroic filters are used at normal incidence and also 45°.