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Starlight Instruments 3.5" Diameter Riser, Adds 3.35" to Length

Starlight Instruments 3.5" Diameter Riser, Adds 3.35" to Length

by Starlight Instruments
SKU SI-R35-3.35
CA$210.00 - CA$210.00
CA$210.00
CA$210.00 - CA$210.00
CA$210.00
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  • Extends optical path by 3.35" (85 mm)
  • Designed for 3.5" diameter Feather Touch focusers
  • Fits all FTF35xx series focusers
  • Threads directly onto the focuser draw tube for maximum rigidity
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Starlight Instruments 3.5" Diameter Riser, Adds 3.35" to Length

    The Starlight Instruments 3.5" Diameter Riser provides a critical 3.35" (85 mm) of additional length for all FTF35xx Feather Touch focusers. It threads directly onto the 3.5" focuser's draw tube, consuming backfocus to bring imaging trains or eyepieces with long optical paths into the focuser's range of travel.

    Add 3.35" of Extension to Your 3.5" Feather Touch Focuser

    This component is a precision-machined spacer designed for a single purpose: to extend the optical path of a 3.5" Feather Touch focuser by exactly 3.35" (85 mm). If your imaging train, binoviewer, or specific eyepiece combination places the focal plane beyond the maximum outward travel of your FTF35xx focuser, this riser provides the necessary mechanical extension to achieve a sharp focus.

    Solving Focus Travel Issues with a 3.35" Riser

    Engineered to integrate perfectly with Starlight Instruments hardware, this 3.5" riser is not a generic extension tube. It threads directly onto the focuser's draw tube, sitting securely below the end cap to create a solid, flex-free connection. This rigid assembly ensures that even heavy camera packages maintain perfect alignment, preventing tilt that can compromise image quality.

  • What problem does the Starlight Instruments 3.5" Riser solve?

    This 3.35" riser solves the problem of having insufficient outward focuser travel. Certain accessories, like some cameras, off-axis guiders, or binoviewers, require the focal point to be positioned far away from the telescope tube. If this distance is greater than your focuser's draw tube can extend, you won't be able to achieve focus. The riser adds a fixed 3.35" of length, pushing your eyepiece or camera back to a point where the focuser can reach the focal plane.

    How do I install the 3.35" Riser on my FTF35xx focuser?

    Installation is straightforward. First, you unthread and remove the end cap (e.g., the 2" compression ring adapter) from your 3.5" Feather Touch focuser's draw tube. Then, you thread the riser directly onto the now-exposed draw tube threads. Finally, you thread your original end cap onto the end of the riser.

    Will this 3.5" riser introduce any flex into my imaging train?

    No. The Starlight Instruments riser is machined from solid aluminum with precision threads that match the FTF35xx focuser perfectly. This ensures a rigid, secure connection that becomes an integral part of the focuser assembly, preventing tilt and flex even with heavy loads.

    Can I use this 3.5" riser with a 2" or 2.5" Feather Touch focuser?

    No, this riser is specifically designed for the 3.5" diameter FTF35xx series of Feather Touch focusers. It will not fit focusers with smaller diameter draw tubes.

    I'm trying to use a binoviewer with my large refractor and FTF35xx focuser, but I can't reach focus. Is this 3.35" riser the right solution?

    It is very likely the correct solution. Binoviewers have a very long optical path and typically require significant outward focus travel. If you run out of travel on your FTF35xx focuser, adding this 3.35" riser will provide the extra length needed to bring the eyepieces into focus.

    My custom imaging train on my Ritchey-Chrétien telescope places the sensor too far away from the FTF35xx focuser to reach focus. Will this 3.35" riser help?

    Yes. This is a classic use case for a riser. When a combination of accessories like an adaptive optics unit, filter wheel, and camera creates an imaging train that is too "long," the focal plane is pushed far out. The 3.35" riser bridges that gap, allowing your FTF35xx focuser's drawtube to bring the camera sensor to a point of sharp focus.

  • Diameter 3.5"
    Added Length 3.35" (85 mm)
    Compatibility All FTF35xx Feather Touch focusers
    Mounting Threads onto the draw tube, below the end cap

    • 3.5" Riser (3.35" Length)

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  • Starlight Instruments 2-Year Warranty