Baader Planetarium flip mirror II Star Diagonal – Astronomy Now

The Baader Planetarium FlipMirror II showing the perpendicular axis and the interior mirror. Note the easy-grip transpose knob on the right and the splined shaft ready for a drive belt. Image: Baader Planetarium.

SThe problem of imaging while monitoring the camera target has existed since the beginning of the age of astrophotography. A solution was sought that would use an already existing telescope accessory, the star diagonal. A right-angle tube with a 45-degree plane mirror that redirects the telescope’s outgoing beam to an observer-friendly angle. It has spared legions of astronomers the pain of a dislocated neck.

To the rescue of astro-imagers, its single 90-degree exit aperture was left in place, but the mirror was given a pivot so it could pivot out of the optical axis, allowing light to pass to a new rear aperture that would do so receive the now undeflected light. The resulting device, called a star diagonal, has rightfully become a standard astronomical accessory. With the introduction of Baader’s FlipMirror II, this development has taken a fascinating step further.

From the box

The first thing that strikes you is how mature and concise the FlipMirror II is. Its minimal dimensions are designed to offer the lowest consumption of back focus – an important consideration given how much gear can end up hanging. It comes with a set of adapters pre-installed, ready to mediate between the telescope and various “downwind” visual and imaging devices. With the adapter ring attachments in mind, Baader has saved themselves that scramble for slotted and grub screw paraphernalia by providing their own FlipMirror toolkit. This consists of no less than four Allen keys, a slotted screwdriver and an M48/T2 pin wrench.

Another possible configuration for the FlipMirror II, in this case with a Canon EOS 6D DSLR camera and a 25mm Baader Polaris I guiding eyepiece. Image: Baader Planetarium.

Fresh out of the box, the first thing to check the flip mirror deployment action. The mechanical performance of this is crucial. Thoughtfully, the button is heavily notched to allow non-slip operation with bare or gloved fingers. The folding mirror button is spring-loaded and provides satisfactory positive movement between its two configurations. This powered lever’s action meets its stop with a firm touch and without an unsavory, harsh metallic clank.

Prepare to use

For my review, I enlisted the services of my 355 mm (14 inch) LX200, an already well run telescope with focus accessories.

My first task was to assess the reflectivity and alignment of the fold mirror, so I arranged adapters to hold matching eyepieces on each of the traditional fold mirror ports – the right angle and rear ports. I had a pair of identical (binocular) eyepieces ready to confirm the equivalence of reflected and direct images. High in the southern sky, a first quarter moon offered itself as a willing test subject.

I found that the lunar surface reflected from the right-angle mirror appeared just as bright as that through the rear aperture, confirming the quality of the multi-coated aluminum reflective surface.

To verify that the two apertures and the mirror were perfectly orthogonal, I focused my telescope on the rim of Mare Crisium and carefully centered Proclus Crater in an eyepiece field. When I turned the mirror over, I was pleased to see that I had exactly the same view in the other eyepiece – excellent evidence of the fine engineering inside the star diagonal. I should add that even if the views were misaligned, it is possible to tweak all the light paths with precision via access screws mounted on the surface of the folding mirror’s cage and then fix it in place with the apex tool of the provided pin wrench .

When observing a star at higher magnification, I could see no evidence of bending, nor could I produce one. The device’s claim to be able to handle heavy loads is undoubtedly justified.

I then proceeded to configuring it conventionally with a CCD camera and a reticulated eyepiece. The pre-installed Baader adapter rings were a great way to achieve this, but as I delved into adapting these to my own gear, not for the first time (and through no fault of Baader) I craved greater uniformity in attaching Accessories another, because at the dawn of the age of astrophotography, the collision of photographic, microscopic, and astronomical equipment resulted in a mismatch of interacting standards that we still endure. Some accessory manufacturers even inexplicably create their own custom connector threads. Luckily, Baader offers a plethora of interface rings for support. As described in Tolkien Lord of the Rings, I long in the dark for “a ring to rule them all”. Perhaps one day a variable diameter multithreaded adapter will appear.

The connectors that connect the Baader Polaris I eyepiece (see image above on previous page) to the FlipMirror II via adapters. Image: Baader Planetarium.

With my Baader Polaris I guide eyepiece on the primary reflected aperture, I was able to easily control my CCD camera’s view on the linear (rear) aperture and took some lunar images for the record. I also found, as previously confirmed, that the center of the field of view was the same for each axis.

Triple assembly

Baader’s FlipMirror II has another mainstay, namely a tertiary (auxiliary) port in the base. Among other things, it offers the simultaneous mounting of an off-axis guider, which cuts off part of the incident beam regardless of the orientation of the folding mirror. This bezel can accommodate either Baader’s own off-axis guider or the older version of Celestron’s Radial Guider (#94176). Not to miss an inventive opportunity, this third port has one more trick up its sleeve. On the back of the folding mirror, an additional reflective zone allows the user to position a calibration lamp during spectroscopic imaging.

I already have the Celestron Radial Guider, so I used that during testing. Attaching the off-axis guider nosepiece requires the interaction of very small grub screws in the base port assembly. Some might find this fiddly, and even on my own assembly, one of the grub screws made a failed attempt for freedom. However, thanks to the kit that came with it, I at least had the necessary tools for the job – and to be fair, a user would probably only perform this delicate installation once.

With three axes of additional equipment, the Baader FlipMirror II handles the load without hesitation. All adapter rings are held firmly without any mechanical movement. The rigidity of the cage under load is amazing – each port is clearly capable of gripping heavy DSLRs, binoculars and other attachments with alacrity. Needless to say, the FlipMirror II can also do this when the accessory requires rotational realignment.

The FlipMirror II, using one of the included Allen keys to adjust the grub screws that align the mirror. Image: Baader Planetarium.
The FlipMirror II is just one of many possible configurations, in this case with a Baader Polaris 1 guiding eyepiece and two cameras. Image: Steve Ringwood.

Baader even went to the trouble of squeezing in two screws on one side of the case to make it possible to attach additional devices or even cable ties. That’s a very good testament to Baader’s confidence in the strength of the FlipMirror II’s body. Speaking of additional features, Baader thoughtfully designed the neck of the flip mirror button with splines to allow for the use of an optional motorized remote control strap.

As with any accessory deployed in the Focus, balance needs to be considered – especially with a device like this that structurally can accommodate any number of additional devices. This is more of a problem with telescopes that are mounted in a yoke, such as the B. fork-mounted Schmidt-Cassegrain telescopes, where the center of gravity cannot be changed by moving along the optical axis. The good news is that the Baader FlipMirror II gets off to a good start despite its own strength of only 195 grams (without adapter rings).

The FlipMirror II comes with various Allen keys, a flathead screwdriver and an M48/T2 pin wrench. Image: Steve Ringwood.


This is a very versatile animal that can adapt to various individual needs. Aside from having to temporarily cannibalize some of my existing devices for additional adapters and collars for this test, the FlipMirror II was a joy to play with. In addition to the function as a high-quality conventional star diagonal and folding mirror, the additional port in its base offers additional functions in the areas of guiding and spectroscopy. In fact, I think it’s fair to call itself an optical hub.

The range of multiple configurations of the frame is supported by Baader’s own extensive range of adapter rings and collars (including, of course, Baader’s universal filter changer). This means that if your needs and requirements change, the Baader FlipMirror II will steadfastly support you under all circumstances.

At a glance

Available ports: 3

weight (without adapter): 195 g Collimable mirror, made of multilayer aluminum with dielectric protection layer, with 94% reflectance.

Accessories included: Side adjustable T-2a top ring, two M48i/S52 dovetail rings, two reducer rings, M48a/T-2i and M48a/T-2a inverter ring M48a/M48a, tool kit, with 3mm screwdriver, four Allen keys, pin wrench

Steve Ringwood is a regular contributor to astronomy now. Baader Planetarium flip mirror II Star Diagonal – Astronomy Now

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