Off-Axis-Guider NIKON M54

NT$6,999

Available on backorder

OAG  Nikon M54JP
Off-axis-guider to adapt NIKON to TAKAHASHI
(with M54x0.75 thread: Takahashi, Vixen step-down)
Lightpath: 9.7mm

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Description

Offaxis Guider for Takahashi & Nikon DSLRs

Maximized stability by avoiding an adjustable guidefinger. With tilt unit and 10mm back-focus. Optimized for Takahashi M54 thread and Nikon DSLRs, incl. T2 guideplatform.

Worlds first: Off Axis Guider for Nikon with tilting Function

This off-axis-guider by Lacerta was specially made to connect Takahashi corrector with M54 thread to Nikon 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 short (S) or long (L) focal ratio

The deflection prism is built in fixed, to avoid the common “OAG diseases” of self-loosening guide fingers, and to control connected reflections or diffraction artifacts. The Lacerta OAG is designed to work with full-frame cameras without introducing vignetting by the guide prism.  To adapt different telescopes, two versions ared offered containing different prism sizes.  These are:

  • S:  full-frame cameras with telescopes from f/3,7  to f/7
    APS-C from f/2,8 to f/4  (Version “S” means “short ratio”, e.g..: FSQ85 with 0.73 reducer)
  • L:  full-frame from f/7 to f/15
    APS-C from f/4 to f/ 15 (Version “L” means “long ratio”, e.g. Takahashi Mewlon with 0.73x reducer)

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.
or…
“L”: Easier guide star search-but shading and possibly a few tender spikes more on the picture!

Good to know

During the development of this OAG, we were confronted of the fact that a Nikon bayonet must be mounted counterclockwise (not clockwise like Canon). Therefore, it seemed impossible for a long time to mount a Nikon Off Axis Guider at all because the battery holder was always in the way. Finally, we have designed a new Nikon-compatible bayonet, which can be mounted clockwise. Further optimisations have also been implemented to accommodate a 6mm guidefinger interior opening in the 8.5mm light path.
And then the tilting function was integrated …

The development took a long time, but we hope that our astrolover friends with Nikon DSLR are more than “satisfied” with the result …

  • Nikon bayonet (APS-C and full frame)
  • M54x0.75 Takahashi connecting thread
  • Light path: 9.7mm (additional 0.0-0.2mm can be adjusted with the tilting function)
  • Backfocus: 9.9mm (the tilting function may add by max. 0,4mm)
  • T2 platform for guide camera (a C-Mount Platform is also available, please specify when ordering)
  • Guide-finger optimized for CS mount guide-cams (up to 12,5mm back-focus)
  • 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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