Off-Axis-Guider CANON M54

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Off-Axis-Guider CANON M54


Available on backorder

Off-axis-guider to adapt Canon EOS to TAKAHASHI
(with M54x0.75 thread: Takahashi, Vixen step-down)
Lightpath: 12.2mm

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Offaxis Guider for Takahashi & Canon EOS DSLRs

No moving parts
Optical Path: 9,5mm. Additional 0,25mm-3,75mm by distance ringset for Takahashi M54 thread.
Incl. T2 Platform for Guidecamera

Worlds first: Off Axis Guider for Canon EOS with tilting Function

This off-axis-guider by Lacerta was specially made to connect Takahashi corrector with M54 thread to Canon DSLRs. Besides that there is a novel feature: An eventual tilting problem can be adjusted by 3 screws on the case housing. If you encounter de-focused stars on one side of your photo, it is possible to adjust the tilt and get perfect stars to the edge. There are 3 little screws on the case housing that adjust little balls inside the OAG body, which emerge on the front side and are able to de-tilt the mechanics. The adjustment can be done without taking off the OAG.

Optimized for Takahashi

The Guide-Prisma was fixed to counteract the many “OAG diseases ” such as adjusting guideprisma, or reflections or diffraction symptoms occurring by the light. Two versions are offered with a smaller or a larger prism. The position of the prism allows for full format cameras up to f/4 (version “S “-short), or up to f/7.3 (version “L “-long “) or slow tubes to be able to work without vignetting.
In most cases the L(ong) version is selected, advantage is that guiding stars are easier acquired. The position of the prism achieves no vignetting when using APS-C cameras up to f/4, Full-Frame Cameras up to f/7.3 or with long tubes (e.g. Takahashi Mewlon with 0.73x Reducer). When using a fast telescope either the “S”-Version can be used or the “L”-Version if small diffraction spikes are acceptable when using the Off-Axis-Guider.

The optical path with 9.5mm is 2.75mm shorter than a Standard Takahashi – Canon DSLR combination requires. Professional photographers know with a shorter focal length (optical design dependent) the optimal distance between flattener and camera sensor can be less. This leaves enough adjustment for a combination with other Takahashi reducers, filters or third-party optics. An M54 spacer ring set (2mm, 1mm, 0.5mm & 0.25mm) for any combination is included for free.

Before you select version “S” or “L”

The ideal position and size of the guide mirror depends on the light path. A high-speed telescope with full-frame camera not only has a steeper, but also a wider beam of light. Accordingly, the guide mirror must move to the side of the light path, far away from the optical axis. Frankly speaking: the positions “S” and “L” are calculated in a way that the guide mirror does not bring any additional shading / diffraction in the primary image (the main camera).

Another thing is whether the guide mirror can get enough light from the lens. It also depends on the focuser or on the various mechanical parts and intermediate optics (flatten detection, free diameter of the correction elements or filters, internal apertures, catadioptric systems, the baffle, etc …). So it may happen that the illumination of the guide sensor is not complete if the light path by the above parts is already “pre-vignetted”. For example, if the radius of the corrector lens is smaller than the distance of the guide mirror from the axis. In extremely bright systems, vignette-free illumination is not even geometrically possible!

So please consider which of the two (geometrically often unavoidable) full-format compromises do you want to accept?
“S”: More difficult guide star search-but without shading on the primary sensor.
“L”: Easier guide star search-but shading and possibly a few tender spikes more on the picture!

  • Canon EF bayonet (APS-C up to f/4 and full frame)
  • M54x0.75 Takahashi connecting thread
  • Light path: 12.2mm (additional 0.0-0.2mm can be adjusted with the tilting function)
  • Spacer ring set for all Combinations (2mm, 1mm, 0.5mm & 0.25mm)
  • T2 platform for guide camera
  • Par-focal position for guide camera: 10.6mm above the end of the guide finger (optimized for MGEN), other guide fingers are possible (e.g. ASI120)
  • Two different prism sizes available (L and S). Please specify when ordering
  • First mount the Lacerta OAG with Tilting balls fully retracted, but pushed to just touch the connecting adapter. Move focuser in about 1mm and make a test photo. The stars should be tiny disks.
  • Analyze the photo and determine the direction of the tilt. Smaller star disks indicate, where the distance to the focal plane is too little and needs to be enlarged. Caution, the camera shows an upside down mirrored image.
  • Slightly loose the M54 thread between OAG and corrector again, max. 20-30 degrees
  • Push out the corresponding tilting ball (or balls) slightly by screwing in the adjustment screw (maybe 1/16 of a turn)
  • Tighten the OAG again, but not too much.
  • Take a new test photo and check if star sizes are same now everywhere. If yes, focus and start session. If no, do another round of adjustment.

Additional information

Weight1 kg
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