What is a SLOAN/SDSS r' filter and why is the Baader filter "photometric"?
A SLOAN/SDSS r' filter is an optical filter that transmits a specific band of red light, as defined by the Sloan Digital Sky Survey, a major professional astronomical survey. The Baader filter is designated "photometric" because it is manufactured to precisely match this scientific standard, allowing astronomers to take brightness measurements (photometry) that are consistent and comparable with data from other observatories worldwide.
Can I use the Baader SLOAN/SDSS r' filter for general astrophotography?
While you can, it's not its primary purpose. The SLOAN/SDSS r' bandpass is designed for scientific measurement, not for creating visually pleasing images. For standard LRGB imaging, a dedicated red filter from a conventional RGB set will produce better color balance when combined with other channels. This filter's strength is data acquisition, not aesthetics.
How do I choose the right size Baader SLOAN/SDSS r' filter for my camera?
Choose the filter size that matches your filter wheel and avoids vignetting. Here's a general guide:
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1.25" Mounted: Best for cameras with smaller sensors (up to ~1-inch class).
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36mm Unmounted: Ideal for cameras with APS-C sized sensors.
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2" Mounted / 50mm Round / 50x50mm Square: Necessary for full-frame (35mm) sensors to ensure the sensor corners are fully illuminated.
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65x65mm and 100x100mm: Reserved for large-format scientific cameras used in professional observatories.
Does the Baader SLOAN/SDSS r' filter require a specific camera to be effective for photometry?
No, the filter will work with any monochrome astronomy camera (CCD or CMOS). The key to photometry is a camera with a linear response to light and low noise. The filter simply ensures that the light reaching the sensor is restricted to the correct scientific bandpass, which is the first step in acquiring reliable data.
How can I use the Baader SLOAN/SDSS r' filter to measure the brightness of asteroid 4 Vesta?
You would take a series of timed exposures of the star field containing asteroid 4 Vesta. Using photometry software, you measure the brightness of Vesta relative to several nearby reference stars of known, stable magnitude in the same images. Because the Baader SLOAN/SDSS r' filter ensures you are measuring in a standard bandpass, your resulting magnitude measurement for Vesta can be accurately compared to official databases and other observers' work.
Will the unmounted 36mm Baader SLOAN/SDSS r' filter fit my ZWO filter wheel?
Yes. The 36mm unmounted filter size is a standard format specifically for use in filter wheels from manufacturers like ZWO, QHY, and others that are designed to pair with APS-C and smaller format astronomy cameras. The filter is held in the carousel by small screws or a retaining plate, depending on the wheel's design.
