These full aperture Solar Filters, are safe glass solar filters that allows as much of the light through as possible through the telescope safely. This allows your telescope’s full aperture to be viewed, giving you the best daytime viewing possible with minimal atmospheric instability. When there is instability, you put a mask over the filter’s end that will reduce the aperture effectively. There is an aluminum cell with this premium solar filter that is centered and secured to the end of the telescope tube by nylon thumb screws using a felt padding. It is made from hand selected glass that is of high quality glass with a reflective coating that has been thoroughly inspected. This high quality glass is durable, providing the market a full aperture solar filter. The image of the sun being viewed has a yellowish-orange natural look when directly viewed through a telescope or for photographs. All of our products are new product and are shipped in good condition in packaging intended for them to arrive in good condition. Spectrum Telescope filters slip over the sky end of the optical tube of the telescope. To get the proper fit, measure the outer diameter by using a caliper, ruler, or tape measure. Measure the widest distance of the telescope end starting from the exterior of the casing, across the center and to the exterior part of the casing of the other side. After you have your measurements, you should order a size larger than what you measured. This is because your measurement is being compared with the solar filter ID (inside diameter). For instance: If you measure 4″ across the optical tube end needs a 4.25” size solar filter. This will make it just a little bigger than the measurement you took. Your O.D. Measurement: 6 1/8” (156mm) to 6 3/8” (162mm)