Field report: „Baader SunDancer II Telecentric System TZ-4S“

This summer we provided our customer Mr. Rüdiger Proske with the new Baader SunDancer II Telecentric System TZ-4S (#1363080 , € 385,-) for a comparison test with the longer TZ-4. Most interesting was the question how the TZ-4S, which was primarily designed for the SunDancer II H-alpha filter, harmonizes with his large SolarSpectrum H-alpha filter. We are very happy about his very positive conclusion and his field report.

Please read the detailed report of Mr. Rüdiger Proske here:

In June 2023 I was offered the opportunity to test the new "Baader SunDancer II Telecentric System TZ-4S" (short TZ-4S) for the upcoming market launch.

Since I had already been working with the classic, long telecentric systems TZ-4 and TZ-3 for 2 years, my interest and curiosity for this TZ-4Short were immediately aroused. I wanted to know how the new system had developed and how it compared to the older TZ-4. It was also very interesting to see how the TZ-4S, which was primarily designed for the SunDancer II H-alpha filter, would work with the SolarSpectrum filter, which was used here.

The test setup

The new TZ-4S was tested on a TEC 140 ED with a native focal length of 980mm in front of a SolarSpectrum Solar Observer 1.5 - 0.5A H-alpha filter. To get the refractor to the necessary focal length aperture ratio of F=30, the TZ-4S is ideally suited. The achieved focal ratio of F=28 is sufficient.

A camera with a Sony IMX174LLJ was used as sensor, which is particularly suitable for solar images due to the global shutter. A Baader D-ERF was mounted in front of the telescope lens to keep the energy out of the telescope.

Unboxing and mechanical impression

The TZ-4S comes in a small, Baader-typical cardboard box. When you hold it in your hands, the TZ makes a solid and robust impression. Spontaneously, one is reminded of an eyepiece, and it can be mistaken for one at first glance. Although it is completely made of metal, it is a bit lighter with approx. 250g than the old system with approx. 310g.

What immediately stands out positively is the compact and short design compared to the significantly longer old system. The satin black surface seems to be identical to that of an eyepiece and promises longevity. Both ends are securely closed by dust caps.

Integration into the image train

On the telescope side, the TZ-4S is inserted into the eyepiece clamp like a 1.25" or 2" eyepiece. I use a 2" Baader ClickLock eyepiece clamp. This allows for quick setup and offers the ability to rotate the H-alpha system as needed.

On the camera side, the TZ-4S has a T-2 thread. This makes it easy to adapt standard components such as T-2 extension tubes or quick-changer. But also an integration into the Baader M68 Tele-Compendium is possible. A minimum of 100mm after the last lens element is specified as backfocus. The distance is usually achieved with T-2 extension tubes. Here I have made the experience that it is quite beneficial to the image quality to increase the distance a little. In the end, I found about 150mm to be optimal. However, the system is very tolerant, as is typical for a TZ (in contrast to Barlow lenses).

The short backfocus is a significant advantage over the old TZ-4, which required at least 240mm as working distance. This significantly reduces the enormous length that an H-alpha setup has. This reduces the load on the focuser and reduces the risk of a mechanical collision during meridian flip.

The entire assembly proved to be mechanically robust with no play or "wobble".

Optical performance

As always, pictures say more than a thousand words. Therefore, I refer you to the pictures below. Visually, however, it can be clearly said that the new system is at least equal, if not superior, to the old one. A direct comparison at Lucky-Imaging is always a bit tricky, since conditions are constantly changing and ultimately a statement is always based on the "stacked" images. However, what I could determine in a direct comparison is that the new TZ-4S was consistently a tad sharper and the images had more reserves in terms of dynamic range. This is probably primarily due to the recalculation of the optical setup and the H-alpha wavelength optimization, which pays off here. 

Size comparsion old and new TZ-4(S) at the telescope


The new "Baader SunDancer II Telecentric System TZ-4S" is a wonderfully compact and high-quality telecentric system that feels at home on both small and large telescopes. Its connection options allow for versatile use. And when stowed away, the system takes up no more space than an eyepiece.

To me, the new TZ-4S represents a consistent and logical evolution of its several-year-old predecessor.


  • Compact
  • Relatively light
  • Robust
  • Standard connections
  • Very short working distance for TZ systems


  • None found in two weeks of use


  • The test system was provided on loan by Baader Planetarium. Many thanks for this!
  • The system was not tested with the SunDancer II, but with a SolarSpectrum.
  • More pictures and solar animations from the author:

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