Lumicon 58mm Minus Violet FilterLumicon 58mm Minus Violet Filter Lumicon 58mm Minus Violet Filter is used primarily to bracket the color corrected band of refracting telescopes. This filter can also be used as a visible filter in RGBV (red green blue visible) astrophotography with reflecting telescopes. Most digital CCD cameras have built in infrared filters, however a minus violet filter may be used in addition depending on how far into the blue your primary lens is color