Baader TZ-3 Telecentric System 2" – Research Grade (3x Focal Length)

 Baader TZ-3 Telecentric System 2" – Research Grade (3x Focal Length)

• Research Grade Telecentric Unit, featuring an oversized pick up expanding lens set and 2" (50.8mm) threads on both sides – T-2 Adapter and 2" m/f inverter ring are both included as standard accessories
• 46mm clear aperture at the H-alpha-filter entrance side - suitable for research-grade SolarSpectrum H-alpha filters
• Large working distance of 250mm for optimised focal length reduction with a telecompressor and suitable room for adapting a binocular viewer
• Aplanatic, with 3x focal length extension to achieve a parallel f/30 beam in conjunction with ~f/10 optics systems – free of field curvature
• Primarily calculated and produced for H-alpha at 656,3 nm, delivering 99% Strehl (definition brightness) depending on the used telescope system
• Diffraction-limited design with about 80% Strehl also at 396 nm (CaK)

Please note: when using as a telecentric for H-alpha or CaK solar observation, it is mandatory to include a suitable enegy protection filter in front of the telescope aperture to prevent damage to the lens groups in the telecentric due to overheating. Heat/melting damage is not a warranty case, but only occurs due to improper operation.

For H-alpha, please use a

• Baader D-ERF Energy Rejection Filter (75 - 290mm) (various versions available)
• for CaK a Baader 2" Cool-Ceramic Safety Herschel Prism Mark II – (Visual / Photo) (various versions available)
• or AstroSolar Photo Film OD 3.8 (various versions available).

The Triband ERF coating of a Triband-SCT - Schmidt-Cassegrain-based Multi-Purpose-Telescope, for Sun and Deep Sky is suitable for both H-alpha and CaK.

Baader Telecentric Systems for focal length extension

For supplying a parallel optical beam and for providing sufficient backfocus, in conjunction with any SolarSpectrum H-alpha filter

Telecentric optics sets are often confused with a barlow lens. Both can be used to increase the focal length. Telecentric assys are designed so that the exit pupil seemingly is positioned at infinity, which means that the center ray from any point in the field appears to come from infinity and is therefore perpendicular to the image plane and parallel to the optic axis. This means that the off axis beam does arrive 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 to a barlow lens - the edge field rays are not tipped bundles.

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 an 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.

Starting from an aperture ratio of ~f/15 (+2x Telecentric), ~f/10 (+3x Telecentric) or ~f/7.5 (+4x Telecentric), the Baader TZ-systems will create a parallel beam with ~f/30 aperture ratio. In the case of largely deviating telescope focal lengths, the clear objective aperture of the telescope should be reduced in diameter to the point that the final resulting f/ratio is close to f/30 again (we do offer a suitable iris-diaphragm for this purpose).

TZ-system working distances – when measured from their rear lens – range from 200mm for the TZ-2 to 230 mm for the TZ-4 - 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 SolarSpectrum body by means of a Baader BBHS T-2 star diagonal. All TZ-coatings are matched to the different lens glass-substrates and optimized for maximum throughput at 656 nm. Still the TZ-3 especially also works for CaK at 396 nm. The TZ-3 Strehl-ratio is well above 80% at 396 nm

IMPORTANT NOTE

Please note that for H-alpha observations below 1 Ang halfbandwidth (FWHM) a telecentric lens system is absolutely mandatory, in order to achieve the recommended focal ratio of f/30 to (preferably) f/40! Because only with a telecentric approach you can create a perfectly parallel optical path which is essential for the unrestricted function of such a complicated etalon.

A TZ-lens-system is an ESSENTIAL prerequisite. One could also optically - or by means of a Barlow lens - bring a telescope to a focal ratio of f/30, but this does not mean at all that a parallel optical path is created. And mind you, a still slightly conical optical path with f/30 sent into an etalon with 0.5 Ang FWHM would only provide the contrast as if the filter had a FWHM of 0.7 Ang or much worse.

It doesn't have to be a TZ-4. The new TZ-3 Telecentric System 2" – Research Grade (3x focal length) (#2459257 , € 445,- ) is much better in terms of optical calculation than the 20 year older TZ-4.  So it makes sense for the user to start with a TZ-3 RG and rather stop down the telescope aperture to get to f/30. This will bring out the real contrast of the chosen SolarSpectrum-filter much better than with a poorly matched system where, for example, the older TZ-4 has a smaller clear aperture than the Solar Spectrum-Etalon would require. In the long run, a newly calculated, large RG TZ-4 is in preparation - it is worth to wait for it and to get familiar with H-alpha observation with the TZ-3 first. In the end one will certainly need both systems (RG-TZ-3 and RG-TZ-4) and adjust the telescope aperture  individually - as the system would require to enable an f/ratio of f/30 at minimum or f/40 as optimum. 

Only AFTER the H-alpha etalon you can extend the field size by reducing the f-ratio with adding the new ResearchGrade telecompressor 0.4 into the optical train.

Basically - a Barlow lens has no place in an H-alpha system!