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Optolong Venus-U Filter

Optolong Venus-U Filter
Price:  £140.00(Inc. 20% VAT)

Product Code:  OPT-VENUS-U-1.25
Brand:  Optolong


Optolong Venus-U Filter 1.25"

The Optolong Venus-U filter makes it possible to obtain photographs, CCD or video images in the UV-A (320-400nm) part of the spectrum and observe Venus' cloud structures.

Compatible with 1.25" eyepieces and other accessories.

Main Use and Performance

When you use it with monochrome CCD cameras you would need to remove the cover glass from the sensor and internal UV-IR blocker in order to pass UV light through.

The same holds true for DSLR cameras...the built-in low pass filter needs to be removed, therefore this filter is only compatible with astro modified dSLR cameras that have no filter in the optical path. What’s more, as most camera lenses are developed for the visible spectrum, these will be not usuable for this type of photography, so you would need a special UV lens attached to the camera body. The sensor of CCD or CMOS cameras is usually capable of detecting light in the 350-1100nm range.

For the above reasons we recommend to use this filter with reflector telescopes (i.e. Newtonian and Ritchey-Cretien telescopes) where there are no lens elements involved, just mirrors as mirrored light will contain the whole spectrum, not only the visible light part.

We will have to test it with SCT, Maksutov and Dall-Kirkham telescopes to see how well these perform with this filter as in those telescopes there is a lens element.

Acts as an outstanding dust shield, which prevents the possibility of dust settling on the lens during long time exposure.

In addition to the above above astronomical use, ultraviolet photography finds practical use in medicine, dermatology, botany, criminology and theatrical applications as well.


Optolong filters are not designed for solar observation. DO NOT LOOK AT THE SUN WITH ANY OPTOLONG FILTER without a proper solar filter (i.e. Baader Astro Solar Safety Film) covering the front of your telescope as permanent eye damage will be the result.

Technical Data

  • Schott substrate material
  • Glass thickness 2.0 mm (1.25”/2”)
  • Surface Quality: 60/40 (Refer to MIL-O-13830)
  • Fine-optically polished to ensure accurate 1/4 wavefront and < 30 seconds parallelism over both surfaces
  • 80% maximum transmission at spectral region 320-370nm.
  • Precision off-band blocking on ultraviolet wavelength 200-280nm, visible and infrared spectral region.

Filter Cell

  • Ultra-thin filter cell minimise vignetting by maximising possible clear aperture (clear aperture is 26mm for 1.25” size and 45mm for 2” size)
  • Aerometal Material
  • Precise CNC Machining
  • Sand Blasting Process
  • Black Anodized Finish
  • Extinction Treatment to Prevent Reflection
  • Laser Engraving No Fading

Available Sizes

  • Standard 1.25” & 2”


  • Plastic PP Case
  • Imported High Pressure EVA Case Lining
  • Silver Cardboard Box
  • High Density Sponge Carton Lining

Optical Coating

  • Multi-layer anti-reflection coating
  • Non-cementing optical substrate coating
  • Electron-beam gun evaporation with Ion-assisted deposition coating technology for durability and resistance to scratching, as well as stability on CWL (central wavelength) no deviation affected by temperature change.
  • Planetary rotation system offers precision and homogenity of coatings ensuring high value on transmission of pass-band and Optical density of off-band. (Please note, "planetary rotation system" is a type of optical coating process and does not refer to the astronomical system describing the motion of the planets in our solar system.)

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