Baader Planetarium Q-Barlow 2.25x / 1.3x
This high-quality 2.25x Barlow made of exotic glasses provides the rare extension factor of 2.25x. So, there are no duplicate focal lengths when used with the eyepieces of the Q-Turret Set, and you can achieve higher magnification than with standard 2x barlow lenses if you do planetary photography with a web or video camera, and you can make better use of the cameras resolution.
Read here the detailed report by Dipl.-Ing W. Paech: Hints + tricks for high-resolution lunar and planetary photography with a video module - a short "workflow" for SC telescopes with Baader accessories.
The Barlow can either be screwed into the Q-Turret eyepiece turret or combined via the special, included adapter with all 1.25 "eyepieces. In this case, it acts as a 2.25x Barlow. With the Q-turret revolver and the Classic Eyepieces, this results in the following focal lengths: 2.7 mm, 4.5 mm, 8 mm and 14 mm
Alternatively, it can also be screwed directly into an eyepiece and then increases the telescope focal length by a factor of 1.3. The Barlow element has an M28.5 male thread (corresponding to the filter thread of 1¼ "eyepieces), the housing has got a M28.5- female thread.
Use on a planetary camera
The bare lens mount of the 2.25x Q-Barlow lens (without the 1.25" eyepiece holder) can be screwed into every 1.25" filter thread. To do so, remove the lenses with their threaded mount from the rest of the housing. Without the eyepiece clamp, the Barlow has no longer an extension factor of 2.25x, but only of 1.3x (when it is screwed completely into the filter thread). The reason for this is the shorter distance between the lenses and the image plane.
It may be that you cant insert the lens mount completely into the filter thread, then the magnification factor is closer to 1.5x.
But if the 1.25" nose piece of a camera provides a M28.5 filter thread, you can usually insert the Barlow completely, and because of the shorter distance the provided factor is ca. 1.3x. This is intentional and was one of the aims of the design. At 2.25x, an image circle of 25 mm is provided free of vignetting, while the fully lit image circle at 1.3x is 13mm.