Off-Axis-Guider NIKON M48

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Off-Axis-Guider NIKON M48


Available on backorder

OAG  Nikon M48EU
Off-axis-guider to adapt NIKON to M48-normed Flatteners
(with M48x0.75 thread: Lacerta, Synta, Baader)
Lightpath: 8.5mm

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Off Axis Guider for Nikon

The most stable OAG we know of, with tilting function and 8.5mm light path, optimized for M48 flattener, including T2 platform for guide-camera.

World first: OAG with tilting function for Nikon DSLR

The LACERTA OAG for M48/Nikon combination has another function: It can be tipped by 3 side screws in each direction about 0.2mm. Thus, production engineered tilting (especially ocular tilting, reducer tilting, sensor tilting in DSLR) can be corrected. To adjust the tilt, the OAG does not have to be removed.

Optimized for M48 Flattener

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 “-long) or slow tubes to be able to work without vignetting. Please provide this information (S or L) when ordering.

Geometry may require shortening the original M48 flattener thread in certain cases. Too long or too wide M48 threads can collide with the guide-prism when screwing in or cover the flow of light to the guide-finger.

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!

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)
  • M48x0.75 flattener thread (GPU, Esprit, Baader etc …)
  • Light path: 8.5mm (additional 0.0-0.2mm can be adjusted with the tilting function)
  • T2 platform for guide-camera camera (on request C-Mount platform, please attach as a note when ordering)
  • Par-focal position for guide camera: 12.5mm above the end of the guide finger
  • 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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