There are eyepieces which already have a built-in kind of barlow element inside of the 1.25" barrel, here you can't insert the Q-Barlow.
2) Using the extension tube with the complete Barlow and adding a few millimetres for the filter thread I make the amplification approximately 2.75x amplification. Is this correct please?
If you screw the Barlow directly into the ca. 23mm long barrel of a Classic Ortho, you get a magnification of ca. 1.3x, if you add the 19mm long Baader 1¼" - 31.8mm nosepiece extension with 1¼" filter thread on both sides (T-2 part #05) # 1905130, you get a distance of ca. 42mm and a magnification of ca. 1.6x.
Please note that these are only approximate values, both because the formula gives only a rough value, and because the position of the field stop varies if you use different eyepieces.
Baader Planetarium Q-Barlow 2,25x / 1,3xWithout the housing, the Barlow lens can be screwed either into the eyepiece revolver (for 2.25x magnification) or directly into an eyepiece (for 1.3x magnification)The Q-Barlow lens can be unscrewed from the eyepiece adapter
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 camera's 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. The factor 1.3x is achieved when the Q-Barlow is completely screwed into the 24mm long push-in sleeve of an eyepiece whose field diaphragm lies 2mm inside the push-in sleeve. This corresponds to the design of our Classic Plössl/Ortho eyepieces; with other eyepiece designs, the magnification factor may vary slightly.
Attention: When fully screwed in, the Barlow element protrudes 13mm into the 1.25" plug-in sleeve. On eyepieces where lens elements in the 1.25" sleeve do not allow the Q-Barlow element to be screwed in, it can only be used in the 1.25" adapter with factor 2.25x. If necessary, you can use it on these eyepieces with the 18.5mm long 1¼" extension sleeve with 1¼" filter thread on both sides: Baader 1¼" - 31.8mm nosepiece extension with 1¼" filter thread on both sides (T-2 part #05) (#1905130, € 14,13)
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 can't 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.
|Inner Connection (lens sided)||Thread, M28,5|
|Outer Connection (lens sided)||Barrel, 1¼"|
|Outer Connection (eyepiece/-camera-sided)||Clamp, 1¼"|
|Clamping System||Screw clamps|
|Magnification (x)||2,25x / 1,3x|
|AR-Coating||High transmission multi-coated (HT-MC)|
|Adaptable to||Q-Turret Okularrevolver und Classic Ortho/Plössl Okulare, 1¼ Okulare|
|Usage||Erweitert die möglichen Brennweiten des Q-Turret Okularsatzes.|
|Barrel Size (in)||1¼"|