Spectroscopy Barlow

The Spectroscopy-Barlow is designed to be used with the Baader  DADOS Slit – Spectrograph (#2458550 , € 2360,- ) or the Baader BACHES Echelle-Spectrograph (#2458600 , € 9485,- ) . The lens cell is attached directly to the SC-thread of the housing of the spectrograph and will then provide a magnification of approximately 1.5x. This matches the f/ratio of telescopes with approximately f/6.8 to the f/ratio of the collimator of the two spectrographs, which were designed for telescopes with f/10. This minimises light loss and lets you use shorter exposure times. 

The diagram shows the amount of light that is directed onto the grating by the collimator. Without Barlow, the loss of light is already noticeable at f/9 and can amount to more than 20% under good seeing conditions; due to the sharper light cone behind the Barlow, the same amount of light is available for analysis on telescopes with f/6.8 (such as the PlaneWave CDK 17 and CDK 20) as at f/10. When attached to the SC thread of the spectrograph, the Spectroscopy Barlow provdes the best illumination of the collimator at a focal ratio of about f/6.8; on slower telescopes, its usefulness decreases especially when the seeing is bad, as shown in the diagram on the right. Please note that the magnification factor of a Barlow depends on the distance and the diagrams only apply to mounting on the SC thread of the spectrograph. Then, the distance to the slit is ca. 50mm, and the magnification factor 1.5x. Increasing the distance to 70mm leads to a magnification of 1.8x, at 90mm, the magnification is 2x.

For installation, please refer to the operating instructions which you can find in the download section of this page.