Astrodon

Discontinued

Please contact Astrodon for any remaining inventory

Replaced by NEW Astrodon Photometrics Sloan and UVBRIc filters.

Astrodon-Schuler UVBRI photometric filters have become a popular, low-cost addition for astronomical photometric measurements.  The American Association of Variable Star Observers (AAVSO) orders the Astrodon-Schuler V filter for its members.  Many of the filters go to universities for research.

Based upon Bessell's 1992 modification of the  Johnson-Cousins design, each filter is made made with several Schott and Hoya colored glasses.  Several of the Schott glasses have been discontinued over the years, such as KG4, that was used in the Is filter.  The current formulations used in Astrodon-Schuler photometric filters are listed below.  Spectra and other properties of individual Schott glasses can be found here. 

Features

• 28 and 48 mm dia.mounted, 50 mm square
• 4 (+/-0.1) mm thick
• No A/R coating to maintain low cost
• Colored glass
• No spectral shifting with faster optics
• Special metal sleeves for 48mm filters to fit in 50mm filter wheels

Astrodon-Schuler filters are thicker (4 mm) will NOT be parfocal with Astrodon LRGB, narrowband or NIR filters (3 mm).  It is noted that the phosphate glass, Schott BG-39, is prone to surface crystallization due to humidity over time that leads to frosting of the glass.  This primarily affects the V filter, since the BG-39 glass is exposed.  The surface of the BG-39 glass incorporated into the Bu filter is not exposed. It is sandwiched between the other two glasses.  Common anti-reflective (MgF2) coatings will not mitigate this problem. More expensive, hard (e.g. BBAR) coatings may help. An alternative solution is to add 1 mm of Schott colorless WG-295 glass over the BG-39 glass in the V filter, but that would mean it is no longer parfocal with the other filters. This is not a ubiquitous problem, but does occur from time to time. Please contact Astrodon .