Filter is an optical device used to select the required radiation wave band.
A common feature of filters is that no filter can make the imaging of celestial bodies brighter, because all filters will absorb certain wavelengths, making objects darker.
Now let’s talk about what the OD value of the filter is often referred to as?
The OD value is the cut-off depth, OD=- log (T), and the transmittance of the filter varies from 0.1% to 0.0001% according to OD1-OD6 and so on..
Narrow band filters produced by Borisun Optics Co., Ltd. are generally less than OD3, that is, less than 0.1%. For example, those below special OD6 need to be customized or glued. The glued ones will save costs, reduce the difficulty, and offer more favorable prices.