We are often asked if Yellow Glass is normal as an Energy Rejection Filter.
It is very normal to have yellow glass for energy rejection. it is also very normal for the ERF glass to rattle in the cell. ERF glass rejects by absorption. Colored glass which absorbs energy will expand. In a tight cell, expanding glass can pinch, cause astigmatism or break.
Yellow is the color of glass we have been using for many years for Hydrogen Alpha energy rejection.
At one time, previous DayStar owner, Del Woods offered RG610 glass for energy rejection filters. RG stands for Red Glass. 610 is the wavelength in nanometers under which light cannot pass. Red glass will block all light below RED light in wavelength. This includes the dangerous UV light and other yellow, green and blue wavelengths of the visual spectrum. IR light is passed through RG610.
The manufacturing method of RG610 is such that it is poured into a block form exactly 6.75" by 6.75" b 6.75". This method means that RG610 red glass can never be manufactured above 6.75" in any dimension. It also means the glass (because it is poured into a form) is subject to bubbles and homogeniety issues within the glass. In recent years, RG610 glass ERF's proved problematic for quality control, with low yields due to bubbles and homogeniety issues.
Upon construction of a number of new wavelengths such as Sodium D Line and Helium D3 line, we began to offer Yellow Glass YG530 as ERF material. This yellow glass is drawn instead of poured in manufacturing, which causes a much better homogeniety and less bubbles for higher quality and yield. The yellow glass blocks all light below the 500nm line of yellow light. It still blocks Green, Blue and most importantly, UV light just the same as RG610 does. However, because it is yellow, it can also pass the 530nm light required to observe the Sodium and Helium lines offered in our standard product line.
DayStar now exclusively manufactures new ERF glass with YG530 Yellow Glass for this reason. A number of Red optical windows remain in inventory and will be shipped to Hydrogen Alpha owners until that stock is depleated and eventually replaced with Yellow Glass.
A yellow glass ERF cannot be used with a Calcium II K line or Calcium II H line filter. These bandpass filters require a different method of energy rejection. We recommend only the UV/IR cut filter for energy rejection of Calcium II K and H line owners. Please see our section on UV/IR application. Note that for Calcium viewing, we ONLY RECOMMEND IDAS BRAND UV/IR cut filters, as other brands fail to pass Calcium wavelength light of 393nm.