Vixen SD81SII Optical Tube Assembly

Vixen SD81SII Optical Tube Assembly
Vixen SD81SII Optical Tube Assembly


Suggested retail price: Contact local dealer

Vixen's standard "photo-visual" SD apochromatic refractor with a handy focal length of 625mm.

Vixen SD apochromatic refractors feature "Super extra-low Dispersion" optical glass in its objective lens. The SD81SII has a ring spacer around the objective lens to make the diffraction pattern of stars visible equally for more refined star images in astrophotography. With the use of an SD reducer HD kit or SD Flattener HD kit, the image circle of 44 mm in diameter is obtained to be used for photography with DSLR cameras with full-frame imaging sensors.

Vixen SD81SII Optical Tube Assembly Description

  • A ring spacer placed around the objective lens refines star images beautifully in astrophotography.

    In the previous SD81S model, a set of three tiny tin foils are placed around the objective lens as a spacer between the doublet lens. The end of the tin foils protruding over the objective lens obstruct the incoming light. As a result, the protruding tin foils make the light of diffraction of stars chipped radially. Exchanging the tin foils for the spacer ring makes the diffraction of the stars' light equal. It allows you to create more refined and beautiful star images in your astrophotography.

  • The SD lens suppresses residual chromatic aberration far below the threshold of visibility.

    A lens of refracting telescopes has chromatic aberration which is caused by different wavelength of visible light (colors) focusing at different distances. The Vixen SD lenses, made of FPL53 super extra-low dispersion glass, allow for correcting the chromatic aberration over a wide spectrum of light.

    The SD lenses focusvisible rays of light from the C-ray(red), d-ray(yellow), e-ray(green), F-ray(blue) to g-ray(violet) at nearly the very same position. As shown in the diagrams of spherical aberration, it verifies that the chromatic aberration is highly corrected over a wide spectrum of light with the SD lenses.
    Especially the g-ray, which affects image contrast, is suppressed excellently. The SD81SII delivers outstandingly sharp images with high contrast for both visual and photographic applications. Moderately bright F7.7 images will satisfy the most demanding visual astronomer or astrophotographer.

  • A short optical tube in length is handy for not only visual observation but also astrophotography.

    The ED81SII optical tube has a moderate short length to enable you to carry and set it up readily. Also, a lightweight optical tube allows you to balance it with fewer counterweights. The ED81S comes equipped with a metal carry handle and the Vixen standard dovetail slide bar M for quick attaching and detaching.
    The provided Flip mirror diagonal switches incoming light to allow for using two eyepieces of different magnifications alternately. Also, you can install a camera on the straight side and view an image through an eyepiece on the right-angled side of the flip mirror diagonal.

  • Full-frame imaging with a DSLR camera.

    Using an SD reducer HD kit or an SD Flattener SD kit, which are available optionally, the SD80SII provides an image circle of 44mm, adequate for taking photos with a DSLR camera. (Photo) M8, M20 nebulae taken with Vixen SD81SII with SD reducer HD kit (compaund focus 496mm) and Pentax K-1 at ISO1600, 49 minutes exposure.

  • Optional accessories to expand your pleasure of taking astrophotography.

    SD Reducer HD Kit: This kit includes a flattener lens to be combined with a reducer lens for a flat and wide imaging field when you use them with the SD81SII, SD103SII, or SD115SII optical tube. The reducer lens reduces a focal length by 0.7X. Direct Wide Photo Adapter 60DX: It is available for Canon EOS or Nikon DSLR cameras. It is possible to change the orientation of a camera for a framing of the photographic field.

  • Wide Photo Adapter 60DX

    Sold and high precision camera adapters for prime focus astrophotography are optionally available for Canon EOS and Nikon. The Wide Photo Adapter 60DX is designed to be an integrated camera mount reducing vignetting to the maximum. They are highly effective with full-frame DSLR cameras, and can be used with SD series refractors (in combination with the SD Reducer HD Kit or SD Flattener HD Kit).


SD81S Optical Tube Assembly

  • Objective lens, effective aperture
    81mm SD (Super ED) apohromatic, multicoated
  • Focal length
  • Focal ratio
  • Resolving power
    1.43 arc seconds
  • Limiting magnitude
  • Light gathering power
    134×unaided eye
  • Focusing mechanism
    Rack-and-pinion, with lock knob
  • Finder scope
    XY Red dot finder II (1×aimimg device)
  • Adapter thread / Visual back
    60mm and 42mm for T-ring / 50.8mm and 31.7mm push fit with flip mirror diagonal
  • Accessories
    Tube rings, Dovetail tube plate, Metal carry handle
  • Photography
    Usable with Prime focus, Eyepiece projection and Afocal imaging
  • Solar observation
    Available with Sun projection screen set B
  • Dimensions / weight
    90mm dia. and 585mm long / 3.6kg (Net 2.3kg)


  • Flip Mirror Diagonal
  • XY Red Dot Finder II
  • Dovetail Slide Bar M
  • Instruction Manual


  • M6 x 18mm screws (2 pcs)
  • Allen wrench 5mm
For availability of products, please contact our local dealers. The specifications are subject to change without notice.

Share this page