The Altair 1.25" Solar Continuum filter enhances sunspots, granulation, and fine photosphere detail.
For use with a prefilter such as the Baader Solar Film filters or Herschel Wedge.
Version 3 coating improvements make this the ultimate solar continuum filter:
- Increased transmission averaging 97.5% for the batch to keep frame rates high.
- Slightly narrower bandpass at 7nm average for the batch for improved contrast.
- Internal reflection "Reflex blocking" coatings to minimise halos through internal reflection.
- Blackened edges improve contrast, and remove any change of edge reflections or light leakage.
- OD5 (0.001%) blocking of unwanted wavelengths in the visual range.
- 200nm to 1250nm IR blocking.
IMPORTANT SAFETY INFORMATION: DO NOT USE THIS FILTER FOR DIRECT SOLAR OBSERVATION! Must be used together with a professional solar filter or Hershel Wedge with Max. 0.024% transmission placed BEFORE this filter. For reflecting telescopes, we recommend Baader solarfilm on the front of the telescope, then screw the filter into a filter holder, camera, or eyepiece. For refractors, the filter should be positioned just in front of the camera or eyepiece with a Hershel Wedge in place. Do not use this filter without a suitable solar pre-filter in place, because it will permanently damage your eyes or camera!
The Solar Contrast Booster works by filtering out UV, IR and visual wavelengths except for a narrow 7nm FHWM green band at 540nm. This greatly increases the contrast of solar features when viewed with the naked eye, colour or mono camera, revealing more detail around sunspots and granulation (fast-developing solar convection cells) in the solar photosphere. Highly recommended for use with either Altair Imaging-Ready Hershel Wedge or Baader Solar Film. NOTE: Do not insert the filter before your Hershel Prism or it will melt, it should be placed just in front of the camera, and will screw directly into the Altair GPCAM 1.25" nosepiece. For Hypercam with 2" nosepiece you can order a 1.25" nosepiece (Product code: ALTAIRH-125IN) or use an Altair Magnetic Filter holder with 1.25" filter slider (Search product code starting with "MAGF" and choose the correct thread for your camera).
Why is transmission centred on 540nm wavelength? 530-540nm is a very desirable wavelength for imaging and observing the sun. The Solar Contrast Booster filter improves performance of any telescope optics such as Refractors, Newtonian reflectors, Maksutovs, Dall Kirkhams, Cassegrains, and SCT's. It's especially recommended with Frauenhofer Achromatic refractors and short focal length ED Doublets, because their optimum performance peaks in this green wavelength by design. In fact, not only Achromats, but most ED triplet and APO refractors traditionally have peak performance at the 530-540nm wavelength, where the human eye shows best sensitivity. 530-540nm is not only the traditional "design benchmark wavelength" for most telescope optics, and also that of most high end interferometry equipment used to configure and optimise telescope lenses. Most colour and mono CMOS cameras also have peak sensitivity and resolution in green! Colour CMOS cameras in particular have an RGGB pixel layout with two green pixels for every one blue and red pixel, for an obvious increase in resolution. The are therefore many benefits in isolating this wavelength to capture those fleeting moments of good seeing.
Altair Solar Contrast Booster filter specifications:
- Standard 1.25" Filter Thread Aluminium Cell
- Band CWL540nm 97.5% transmission FWHM 7nm
- 1.85mm thick optical glass λ/4, Parallelism (arcsec) 30"
- Si02 "hard" overcoat with UVIR Block 200-1250nm and Anti-Reflection Coating
