Astronomy Specialist


$369.00 AUD
SKU: BA2458055

Baader Planetarium

  • Optical thickness: 55 mm, 59 mm


The Baader FlipMirror II Star Diagonal is an elegant solution for connecting multiple different types of accessories in the same optical path.

Telescope auxillary instruments cover a wide range of interests, from a sole eyepiece, to camera use, to high end spectroscopy. Unfortunately every telescope just features one exit port. This causes relentless manual exchange of parts in the dark, causing huge time loss, wear on the parts - and "nerves". And whenever you start controlling your telescope remotely - the single port becomes a painful reality.

Improving workflow, especially during astrophotography is the goal set out for the BFM II. This is not just a simple flip mirror but much more, as there are three ports to be put into action.


BFM II makes your single telescope port variable - to suit your various interests

The FlipMirror II Star Diagonal allows a variety of permanent adaptations to your telescope 1 . Use the rotary knob 2 to switch between the rear port 3 and the top port 4; you can use an optional toothed belt to operate it with a motor (not included). An autoguider or a calibration lamp can be connected to the bottom port 5.

General Function of the FlipMirror II Star Diagonal

The BFM II lets you switch between a straight light path (Position A) for a camera or other measuring instruments and an angled light path (Position B), e.g.
for an eyepiece. The following figure shows how it works. In addition, a calibration lamp for spectrographs or an Off-Axis-Guider pickoff-prism (that is not affected by the mirror position) can be connected at the AUX-port on the bottom.




  • Baader-FlipMirror II Star Diagonal (BFM II) with three ports:
  • Straight-through (S52, M48 and T-2 on both sides) for full-frame camera, spectrograph, or other instruments
  • Adjustable T-2 thread on top for eyepiece clamps, video modules (up to 32 mm image circle) or even a binoviewer
  • Bottom flange for the optional Off Axis Guider for Baader FlipMirror II (BFM-OAG) (BA2956951) or for an optional calibration lamp for quick calibration of spectra without removing the spectrograph
  • Precise surface-mirrored flip mirror with multi-layer Al coating, for high-resolution images with cameras with small pixels
  • The back of the flip mirror is also Al coated and masked to direct the light of an optional calibration lamp onto the slit of a spectrograph
  • Enables precise adjustment of all light paths
  • Shortest possible overall length for any application – compatible with a large number of adapters from the Baader Astro T-2 system, the M48 system and the UFC system (Universal Filter Changer)
  • Rotatable M48 connection rings made of hardened, stainless steel on front and rear, backlash-free adapted to the BFM housing. Can be fixed in the optimum position to rotate any accessory around the optical axis.
  • Prepared for an optional toothed belt for motorization (e.g. by Steeldrive II motor focuser with Controller (BA2957165) – basic requirement for image acquisition, guiding and spectroscopy in remote observatories


Optical length
55 mm with S52, 59 mm with M48/T-2
63 x 77 x 69 mm
Connection telescope side M48 x 0.75, M42 x 0.75 (T2), S52, dovetail clamp
Connection camera side M48 x 0.75, S52, dovetail clamp
Weight 240 g
SKU BA2458055





  1. Baader FlipMirror II Star Diagonal – with fine-optically polished, movable mirror
  2. Laterally adjustable T-2a top ring
  3. 2x M48i / S52 Dovetail ring made of hardened stainless steel # 2958552
  4. Reducing ring M48a / T-2i # 2958553
  5. Reducing ring M48a / T-2a # 2958554
  6. Inverter ring M48a / M48a # 2958555
  7. Pin type face wrench for M48 / T-2 and M4 counter nuts
  8. 3 mm screwdriver for M 4 brass adjustment screws
  9. 4x hex keys (2.5 / 2.0 / 1.5 / 1.3 mm). The 2.0 mm wrench has a ball head to reach screws even when accessories are mounted by holding the wrench at an angle.
  10. Bottom flange (laterally adjustable 1mm) for off-axis guide or calibration lamp for spectroscopy
  11. Dust cap for bottom flange
  12. M48 dust cap
  13. T-2 dust caps

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$369.00 AUD

Optical design

Image circle

Focal ratio


Focal length

Optical thickness

Optical thickness: 55 mm, 59 mm



Colour or Mono

Pixel size

Sensor dimensions


Sensor diagonal

Quantum efficiency

Read noise

Fullwell capacity

Bit depth


Camera backfocus

Filter size

Filter size

Bandpass (FWHM)

Bandpass (FWHM)

Glass thickness

Mount type

Payload capacity

Latitude range

Dovetail saddle

Slew speed


Periodic error correction

Counterweight shaft

Azimuth adjustment range

Internal diameter

Illuminated diameter

Compatible telescope external diameter





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