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IMPORTANT: Our store is located in Canada. All orders that include products manufactured outside of Canada or USA will be subject to tariffs and duties, regardless of the order value. US customers are responsible for all applicable duties and tariffs, and those will be billed by the carrier, except for the Lacerta upgrade kit, for which we collect them at checkout.
Baader Photometric UBVRI-U Individual Filter

Baader Photometric UBVRI-U Individual Filter

by Baader Planetarium
SKU BAA-2961750U
$207.00 - $940.00
$207.00
$207.00 - $940.00
$207.00
Price Match Policy!
  • Conforms to the Johnson-Cousins/Bessel U-Band Photometric Standard
  • Designed for Scientific Photometry of Variable Stars and Stellar Classification
  • Planeoptically Polished Substrate for Zero Image Degradation
  • Life-Coat™ Hard Coatings for Durability and Resistance to Aging
  • Available in Multiple Formats from 1.25" Mounted to 100x100mm Unmounted
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Downloads
  • Warranty

  • Baader Photometric UBVRI-U Individual Filter

    The Baader Photometric UBVRI-U Filter provides scientifically rigorous ultraviolet data by adhering to the Bessel U-band standard, available in research-ready formats from 1.25" mounted to 100x100mm unmounted for consistent stellar classification and variable star observation. This is not an imaging filter for creating color composites; it is a scientific instrument for collecting precise, repeatable measurements of stellar brightness in the near-ultraviolet spectrum.

    The U-Bessel Standard: Precision Ultraviolet Photometry

    This filter is designed to strictly conform to the U-band passband of the standardized Johnson-Cousins/Bessel UBVRI system. This system is the bedrock of modern photometry, allowing astronomers worldwide to produce comparable data. The U-filter isolates a specific slice of the near-ultraviolet spectrum, critical for analyzing the hottest, most energetic stars and phenomena.

    By using the Baader U-Filter, your measurements of O- and B-type stars, cataclysmic variables, or active galactic nuclei can be directly compared to professional datasets. It transforms your imaging setup into a tool for genuine scientific inquiry, enabling you to contribute to pro-am collaborations and long-term monitoring projects.

    Research-Grade Optical Integrity for Data Stability

    A filter's photometric accuracy depends on more than just its transmission curve; the physical substrate must be flawless. Each Baader Photometric Filter is made from a planeoptically polished substrate, ensuring it does not introduce any wavefront error to the optical path. The glass is perfectly homogeneous, guaranteeing consistent transmission across the entire field of view.

    To ensure your data is valid for years to come, Baader employs advanced hard-coating techniques (Life-Coat™) that are dielectrically sealed at the edges. This process makes the coatings impervious to moisture and aging, preventing the bandpass from shifting over time—a critical requirement for any long-term variable star research.

    Photometric U-Filter vs. Standard UV/IR Cut Filters: A Scientific Instrument

    It's crucial to understand the distinction between this photometric filter and a standard UV/IR cut (Luminance) filter used for deep-sky imaging. A UV/IR cut filter is designed for broadband transmission of the entire visible spectrum while blocking the unfocused ends. Its goal is to maximize signal for aesthetically pleasing images.

    The Baader U-Filter does the opposite: it aggressively blocks all visible and infrared light to isolate only the scientifically valuable U-band. Using this for general imaging would result in a very dim, monochromatic image with low signal. Its purpose is not visual appeal but quantitative measurement, making it an essential tool for the serious amateur astronomer focused on data collection.

  • What is the Baader Photometric U-Filter primarily used for?

    The Baader Photometric U-Filter is a scientific instrument used for photometry—the precise measurement of starlight. Its primary applications include observing variable stars, classifying stars based on their color temperature (especially hot, blue O- and B-type stars), and studying energetic astronomical objects that are bright in ultraviolet light.

    How is the Baader U-Bessel filter different from a standard UV/IR cut filter?

    A standard UV/IR cut filter is designed to pass the entire visible spectrum while blocking ultraviolet and infrared light, maximizing signal for color imaging. The Baader U-Bessel filter does the opposite: it is designed to block all visible and IR light, passing only a very specific, standardized band of near-ultraviolet light for scientific measurement.

    Can I use the Baader Photometric U-Filter for visual observing or general astrophotography?

    No, this filter is not suitable for visual use or for creating typical color astrophotos. Your eye is not sensitive to the ultraviolet wavelengths it passes, so everything would look dark. For imaging, it isolates such a narrow band of UV light that the resulting signal would be very low and not useful for creating a standard LRGB or narrowband image.

    Why is it important that the Baader U-Filter is "photometric"?

    "Photometric" means the filter's transmission curve strictly adheres to the established scientific U-Bessel standard. This ensures that brightness measurements you take can be accurately compared to data from other observers and professional observatories around the world. It guarantees your data is consistent, repeatable, and scientifically valid.

    How would I use the Baader Photometric U-Filter to study a variable star like Algol (Beta Persei)?

    You would take a series of timed exposures of Algol using the Baader U-Filter with a monochrome camera. By measuring Algol's brightness relative to nearby, non-variable comparison stars in each frame, you can plot its light curve. The U-band is particularly useful for eclipsing binaries with hot stars like Algol, as it reveals temperature changes with high contrast.

    I want to classify hot stars in the Orion Nebula (M42) with my 11" SCT. Is the Baader U-Filter the right choice?

    Yes, it is the ideal choice. The hot, young O- and B-type stars of the Trapezium Cluster within M42 are extremely bright in ultraviolet light. By measuring their brightness through U, B, and V filters, you can calculate their color indices (e.g., U-B) and determine their spectral type and temperature with high accuracy, even from a backyard setup.

  • Filter Type Photometric Johnson-Cousins/Bessel U-Band
    Available Sizes 1.25" Round Mounted, 2" Round Mounted, 31mm Round Unmounted, 36mm Round Unmounted, 50mm Round Unmounted, 50x50mm Square Unmounted, 65x65mm Square Unmounted, 100x100mm Square Unmounted
    Net weight (kg) 0.01 (1.25" Round Mounted, 2" Round Mounted, 50mm Round Unmounted)
    0.02 (50x50mm Square Unmounted)
    0.03 (65x65mm Square Unmounted)
    0.08 (100x100mm Square Unmounted)
    Filter size 1.25 inch (1.25" Round Mounted)
    2 inch (2" Round Mounted)
    31 mm (31mm Round Unmounted)
    36 mm (36mm Round Unmounted)
    50.4 mm (50mm Round Unmounted)
    50 x 50 mm (50x50mm Square Unmounted)
    65 x 65 mm (65x65mm Square Unmounted)
    100 x 100 mm (100x100mm Square Unmounted)
    Filter shape round (1.25" Round Mounted, 2" Round Mounted, 31mm Round Unmounted, 36mm Round Unmounted, 50mm Round Unmounted)
    square (50x50mm Square Unmounted, 65x65mm Square Unmounted, 100x100mm Square Unmounted)
    Single or Set? Single Filter
    Filter mounted Mounted (LPFC 6mm) (1.25" Round Mounted, 2" Round Mounted)
    Unmounted (31mm Round Unmounted, 36mm Round Unmounted, 50mm Round Unmounted, 50x50mm Square Unmounted, 65x65mm Square Unmounted, 100x100mm Square Unmounted)
    Filter Usage CMOS, CCD, UBVRI
    Special Features Life-Coat™ Warranty
    Filter Thickness (without cell) 2 mm (1.25" Round Mounted, 2" Round Mounted, 31mm Round Unmounted, 36mm Round Unmounted)
    3 mm (50mm Round Unmounted, 50x50mm Square Unmounted, 65x65mm Square Unmounted, 100x100mm Square Unmounted)
    CWL (Central Wavelength) UBVRI-U
    Transmission Range Transmission according to Bessel
    AR-Coating Reflex-Blocker™ hard coated, planeoptically polished
    Suitable for f/ratio f/15 to f/1.8
  • Baader Planetarium Warranty