The Baader Planetarium Telecentric Systems are to be used in conjunction with the Solar Spectrum H-Alpha solar filters. They are required in order to obtain a parallel f/30 optical beam (and for providing sufficient back focus), for the Solar Spectrum H-alpha filters.
The Telecentric systems are available in the following focal length extensions:
- 2x - for ~f/15 refractor telescopes
- 3x - for ~f/10 telescopes
- 4x - for ~f/7.5 telescopes
For telescopes with largely deviating focal lengths, the clear objective aperture of the telescope should be stopped down (reduced in diameter) to the point that the final resulting f/ratio is close to f/30. To help achieve this Baader Planetarium offer a suitable iris-diaphragm for this purpose (see their stepless variable diaphragm #2459300).
The TZ-system working distance to the camera sensor – when measured from their rear lens – ranges from 200mm for the TZ-2 to 230 mm for the TZ-4 and to 250 mm for the TZ-3. This provides enough room for the H-alpha filter housing and most any accessories, e.g. a Baader 2" mirror diagonal or any conceivable camera device. The generous room of the TZ-3 will also accommodate a binocular viewer when it is mounted onto the Solar Spectrum H-alpha system body by means of the Baader BBHS T-2 star diagonal. The TZ-3 also has 46mm of clear aperture and is diffraction limited at 396nm (CaK). All TZ-coatings are matched to the different lens glass-substrates and optimised for maximum throughput at H-alpha/656 nm.
Telecentric optic sets are often confused with a barlow lens as both can be used to increase the focal length and ratio. Telecentric systems are designed so that the exit pupil is seemingly positioned at infinity, meaning that the centre ray from any point in the field appears to come from infinity and is therefore perpendicular to the image plane and parallel to the optical axis. This means that the off axis beam arrives at the image plane with the same angular geometry as the axial rays. All field elements look as if they where on axis, across the image plane and, unlike in a barlow lens, the edge field rays are not "tipped bundles".
With a rear mounted Solar H-alpha filter system in use, because all the principal rays across the image plane are perpendicular to the image plane, the rays at the edge of the field will pass through the etalon just in front of the focal plane with exactly the same geometry as the rays on axis. So in an f/30 telecentric optical arrangement, the etalon sees the exact same geometry clear across the field, and the spectral bandpass does not shift in wavelength across the entire field of view.
||2459255 (2x) : 2459257 (3x) : 2459256 (4x)
|FOCAL LENGTH EXTENSION
||for H-alpha observation with SolarSpectrum Filters
|INNER CONNECTION (LENS SIDED)
||Thread, T-2 (M42 x 0,75)
|OUTER CONNECTION (EYEPIECE/-CAMERA-SIDED)
||Thread, T-2 (M42 x 0,75)