Because they are made for H-apha-filters, they are designed for 656.3 nm (the red H-alpha-light); only the TZ3 is also designed to work at 396 nm very good, although then the focal plane is shifted for ca. 5mm.
For visual observations in other parts of the visual spectrum, you need a Barlow, not a Telecentric.
2) Is the middle section intend for removal to provide for an alternate closer location of pickup lens or is this just a manufacturing convenience to be a separate part (reuse of existing parts?)?
3) What would be the characteristics of the resulting output beam? Diameter, F#, impact on position of TZ relative to main objective (assume that would not change), impact on distance from TZ to final focal plane which was originally 250mm?
Answers for individual questions:
1) The middle intersection roughly marks the position of the initial instrument focal length. The middle section cannot be removed.
2) The middle intersection bears a mask (straylight shield). No part of this product is being "reused" on any other product.
3) A large deviation from the designed 250 mm focal lenght is not advisable. Noticeable deterioration of the image contrast would be inevitable.
We have analyzed the optics inside the Quark for instance - and we must be too stupid maybe, but according to our calculation the resulting monochromatic spot diagrams look horrible. So yes - you certainly can try to trim down the TZ-optical principle in terms of shorter FL and small lens sizes. But we conclude that a lot of contrast (and image brightness) goes bust that way. So please do not try to move inward the exiting lens on the TZ-3 - the optical quality will be gone - and the warranty too.
Better look into the solar telecompressor 0.4x that we had designed to work perfectly with the TZ-3. The image will be "very bright" as you end up with an f/10 beam when the incoming FL was set to f/10 as well.
We will continue to look for alternative optical solutions for small etalons, but certainly it must be way better than what we find in the market right now.
2. Second difference I can spot - I see that TZ3 is optimized for 2 lines, while TZ4 is only for 1 line. Is it difference only on coatings or optical design too?
3. Should I expect same high quality when using TZ4 at Ha as on TZ3 at Ha?
4. I can also see that case is different. Is there any reasoning/causes for that? I see that TZ3 fits in 2" focuser, while TZ4 has weird shape and can only be mounted by the thread, or I am missing something.
2. No it is a more elaborate optical design to cover both wavelengths
3. Yes - if you only intend to use it on H-alpha and if the entrance window of your H-alpha filter is not larger than 36 mm
4. No - the TZ-3 has another shape owing to it´s larger lenses. Also it does feature 2" SC-threads as well as reducers for T-2 (M42x0,75 mm). Only the TZ-3 can be mounted straight onto the back end of Celestron Schmidt-Cassegrain telescopes to - also - work with our new generation of Triband-SCTs: https://www.baader-planetarium.com/en/telescopes/baader-planetarium/triband-sct-schmidt-cassegrain-based-multi-purpose-telescope-for-sun-and-deep-sky.html
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
Please also note the detailed PDFs under the Tab "Downloads" for further information
|Focal length extension||3x|
|Usage||for H-alpha observation with SolarSpectrum filters|
|Inner Connection (lens sided)||Thread, T-2 (M42 x 0,75), 2" (50,8mm)|
|Outer Connection (lens sided)||Thread, 2" (50,8mm)|
|Outer Connection (eyepiece/-camera-sided)||Thread, T-2 (M42 x 0,75), 2" (50,8mm)|